The Blockchain Developer 978-1-4842-4847-8 – DOKUMEN.PUB

Table of contents : Contents……Page 3Blockchain Basics……Page 13Intro to Cryptoeconomics……Page 14Blockchain Explained……Page 20Cryptocurrencies Overload……Page 25Blockchain P2P Network……Page 29Summary……Page 42Running a Blockchain Node……Page 43Bitcoin Core API……Page 64Summary……Page 84Creating own Blockchain……Page 85Basic P2P Network……Page 86Genesis Block & Sharing Blocks……Page 98Registering Miners & creating New Blocks……Page 106Storing Blocks in LevelDB……Page 113Blockchain Wallet……Page 117API……Page 121Command-Line Interface……Page 125Where to go from here……Page 130Summary……Page 131Bitcoin Core RPC Resources……Page 132Bitcoin Wallet……Page 134Transactions……Page 140Bitcoin Colored Coins……Page 178Summary……Page 182Ethereum Wallets & Smart Contracts……Page 183Ganache Simulated Full-Node Client……Page 187IntelliJ IDEA Plugin for Solidity……Page 188Truffle Suite……Page 189Compile with Remix……Page 203Private Ethereum Blockchain with Geth……Page 205Connect the Mist Ethereum Wallet to Private Network……Page 212MetaMask……Page 216Public Testnet……Page 219Summary……Page 221EOS.IO Wallets & Smart Contracts……Page 223Testnet Environment……Page 226″HelloWorld” Smart Contract……Page 244Smart Contract IDE……Page 247Compile a Contract & generate ABI……Page 248Deploy a Contract……Page 250Smart Contact Tokens……Page 251Connecting to Public Testnet Block Producer……Page 255Connecting to Mainnet……Page 261Summary……Page 265NEO Blockchain & Smart Contracts……Page 267NEO’s High-Level Blockchain Architecture……Page 268Local Environment……Page 272Local NEO Private Testnet……Page 281Publish Smart Contract on Private Testnet……Page 300Ethereum vs EOS vs NEO……Page 302Where to go from here……Page 307Summary……Page 308Hyperledger……Page 309Hyperledger Overview……Page 310Hyperledger Fabric……Page 314Installing Hyperledger Fabric & Composer……Page 318Hyperledger Composer……Page 335″Hello, World” with Playground……Page 336Deploying on Local Hyperledger Fabric Network……Page 350Running the “hello-network” Network……Page 351Where to go from here……Page 353Error Troubleshooting……Page 354Summary……Page 357Build Dapps with Angular 1……Page 359What is a DApp……Page 360Why Angular……Page 367Summary……Page 404Build Dapps with Angular 2……Page 405Transfer a Smart Contract……Page 406Link with the Ethereum Network……Page 416Connect to MetaMask……Page 423Where to go from here……Page 427Summary……Page 428Security & Compliance……Page 429Security & Compliance Readiness……Page 431Common Blockchain Attacks……Page 441Development Cycle……Page 466Where to go from here……Page 475Summary……Page 476Blockchain beyond Crypto……Page 477Harnessing Blockchain……Page 478Decentralization of Industries & Verticals……Page 484Summary……Page 510Index……Page 512

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The Blockchain Developer A Practical Guide for Designing, Implementing, Publishing, Testing, and Securing Distributed Blockchain-based Projects Elad Elrom The Blockchain Developer Elad Elrom New York, NY, USA ISBN-13 (pbk): 978-1-4842-4846-1 ISBN-13 (electronic): 978-1-4842-4847-8 © 2019 by Elad Elrom Any source code or other supplementary material referenced by the author in this book is available to readers on GitHub via the book’s product page, located at For more detailed information, please visit Contents Chapter 1: Blockchain Basics���������������������������������������������������������������1 Introduction to Cryptoeconomics��������������������������������������������������������������������������2 Ig-pay Atin-lay�������������������������������������������������������������������������������������������������3 Blockchain Explained��������������������������������������������������������������������������������������������8 Blocks + Chain = Blockchain��������������������������������������������������������������������������9 Cryptomining by Cryptominers����������������������������������������������������������������������13 Cryptocurrency Wallet�����������������������������������������������������������������������������������13 Cryptocurrencies Overload���������������������������������������������������������������������������������13 Bitcoin Digital Cash���������������������������������������������������������������������������������������14 Tokens�����������������������������������������������������������������������������������������������������������15 Alternative Cryptocurrency Coins (Altcoins)��������������������������������������������������15 Blockchain P2P Network�������������������������������������������������������������������������������������17 Consensus Mechanism����������������������������������������������������������������������������������18 Proof of Work, Proof of Stake, and Delegated Proof of Stake������������������������19 Mining Layer��������������������������������������������������������������������������������������������������27 Propagation Layer�����������������������������������������������������������������������������������������28 Semantic Layer����������������������������������������������������������������������������������������������28 Application Layer�������������������������������������������������������������������������������������������29 Summary������������������������������������������������������������������������������������������������������������30 Chapter 2: Blockchain Nodes�������������������������������������������������������������31 Running a Blockchain Node��������������������������������������������������������������������������������31 Create a Bitcoin Miner�����������������������������������������������������������������������������������32 Create a NEO Bookkeeping Node������������������������������������������������������������������36 Create an EOS Block Producer����������������������������������������������������������������������49 Bitcoin Core API���������������������������������������������������������������������������������������������������52 Serialized Blocks�������������������������������������������������������������������������������������������61 Block Header�������������������������������������������������������������������������������������������������63 Block Version�������������������������������������������������������������������������������������������������65 Bitcoin Wallet�������������������������������������������������������������������������������������������������71 Summary������������������������������������������������������������������������������������������������������������72 Chapter 3: Creating Your Own Blockchain������������������������������������������73 Creating a Basic P2P Network����������������������������������������������������������������������������74 Creating Genesis Block and Sharing Blocks�������������������������������������������������������86 Registering Miners and Creating New Blocks�����������������������������������������������������94 Storing Blocks in LevelDB���������������������������������������������������������������������������������101 Creating a Blockchain Wallet����������������������������������������������������������������������������105 Creating an API��������������������������������������������������������������������������������������������������109 Creating a Command-Line Interface�����������������������������������������������������������������113 Where to Go from Here�������������������������������������������������������������������������������������118 Summary����������������������������������������������������������������������������������������������������������119 Chapter 4: Bitcoin Wallets and Transactions������������������������������������121 Bitcoin Core RPC Resources�����������������������������������������������������������������������������121 Bitcoin Wallet����������������������������������������������������������������������������������������������������123 Create a Legacy Wallet Address and Retrieve Private Keys������������������������124 Pay to Witness a Public Key Hash (P2WPKH): SegWit Soft Fork������������������126 Elliptic Curve Digital Signature Algorithm���������������������������������������������������127 Transactions������������������������������������������������������������������������������������������������������129 Simple Command����������������������������������������������������������������������������������������130 Testnet���������������������������������������������������������������������������������������������������������132 Viewing Transactions on Block Explorer������������������������������������������������������134 Sending Testnet Coins via the Bitcoin Core Wallet GUI��������������������������������137 Generating Raw Transactions with One Output�������������������������������������������149 Transactions that Require Multisignature����������������������������������������������������157 Setting Electrum with a Multisignature Wallet��������������������������������������������157 Replaceable Transactions and Locktime�����������������������������������������������������166 Bitcoin Colored Coins����������������������������������������������������������������������������������������167 Sending a Transaction with OP_RETURN�����������������������������������������������������167 Bitcoin’s Colored Coins��������������������������������������������������������������������������������170 Summary����������������������������������������������������������������������������������������������������������171 Chapter 5: Ethereum Wallets and Smart Contracts��������������������������173 Ganache Simulated Full-Node Client����������������������������������������������������������������177 Install Ganache��������������������������������������������������������������������������������������������177 Ganache CLI: Listen to Port��������������������������������������������������������������������������178 IntelliJ IDEA Plugin for Solidity��������������������������������������������������������������������������178 Truffle Suite�������������������������������������������������������������������������������������������������������179 Create Your Smart Contracts�����������������������������������������������������������������������181 Connect Truffle to the Ganache Network�����������������������������������������������������183 “Hello, World” Smart Contract���������������������������������������������������������������������184 “MD5SmartContract” Smart Contract���������������������������������������������������������186 Create Truffle Migration Files for Your Smart Contract Deployment������������187 Compile Your Smart Contract with Truffle����������������������������������������������������188 Deploy the Smart Contract to Your Development Network��������������������������189 Truffle Console���������������������������������������������������������������������������������������������190 Interact with Your Smart Contract via the Truffle CLI�����������������������������������191 Compile with Remix������������������������������������������������������������������������������������������193 Private Ethereum Blockchain with Geth������������������������������������������������������������195 Initialized Geth Private Blockchain��������������������������������������������������������������195 Geth Console�����������������������������������������������������������������������������������������������197 Mine Ethereum for Your Private Testnet������������������������������������������������������198 Deploy Remix to Geth����������������������������������������������������������������������������������199 Deploy Truffle to Geth����������������������������������������������������������������������������������200 Useful Commands in Geth���������������������������������������������������������������������������201 Connect the Mist Ethereum Wallet to Your Private Network�����������������������������202 Others to Interact with Your Smart Contract������������������������������������������������203 MetaMask���������������������������������������������������������������������������������������������������������206 Public Testnet����������������������������������������������������������������������������������������������������209 Syncing Blocks��������������������������������������������������������������������������������������������209 Public Testnet Faucet����������������������������������������������������������������������������������210 Ethereum Mainnet���������������������������������������������������������������������������������������������211 Recommended Tools for Smart Contracts���������������������������������������������������������211 Summary����������������������������������������������������������������������������������������������������������211 Chapter 6: EOS.IO Wallets and Smart Contracts�������������������������������213 Setting Up a Testnet Environment���������������������������������������������������������������������216 Install EOS.IO�����������������������������������������������������������������������������������������������216 Install EOSIO.CDT�����������������������������������������������������������������������������������������218 Build EOS.IO�������������������������������������������������������������������������������������������������220 keosd and nodeos Configuration Files��������������������������������������������������������220 Create and Manage a Wallet with cleos������������������������������������������������������221 EOS.IO Wallets���������������������������������������������������������������������������������������������222 Delete and Back Up Wallets�������������������������������������������������������������������������223 EOS.IO Wallet with Custom Name����������������������������������������������������������������223 EOS.IO: Open, Lock, and Unlock a Wallet�����������������������������������������������������224 Generating EOS.IO Keys�������������������������������������������������������������������������������224 Spin Up a node with nodeos������������������������������������������������������������������������227 Re-spin Up a Testnet Local node (nodeos)��������������������������������������������������229 EOS.IO Accounts������������������������������������������������������������������������������������������230 Wallets, Keys, and Accounts: Complete Commands������������������������������������233 Custom, Single Signature (Single-Sig), and Multisignature (Multisig)���������234 “HelloWorld” Smart Contract����������������������������������������������������������������������������234 “HelloWorld” Smart Contract Accounts�������������������������������������������������������234 “HelloWorld” C++ Code�������������������������������������������������������������������������������235 Smart Contract IDE��������������������������������������������������������������������������������������������237 Compile a Contract and Generate an ABI����������������������������������������������������������238 Ricardian Contracts�������������������������������������������������������������������������������������238 Deploy a Contract����������������������������������������������������������������������������������������������240 Interact with a Smart Contract Action���������������������������������������������������������������241 Smart Contact Tokens���������������������������������������������������������������������������������������241 Create Accounts������������������������������������������������������������������������������������������241 Compile wasm with the Latest eosio.token Code����������������������������������������242 Deploy eosio.token��������������������������������������������������������������������������������������242 Create the EOS.IO Token������������������������������������������������������������������������������243 Issue Tokens������������������������������������������������������������������������������������������������244 Transfer Tokens�������������������������������������������������������������������������������������������244 Connecting to a Public Testnet Block Producer������������������������������������������������245 Buy Resource Allocation on the Public Testnet Block Producer������������������248 Publish Your HelloWorld Contract on the Public Testnet������������������������������250 Connecting to Mainnet��������������������������������������������������������������������������������������251 Resource Allocation Explained��������������������������������������������������������������������253 Buy RAM on Mainnet�����������������������������������������������������������������������������������253 Create an EOS.IO Account on Mainnet���������������������������������������������������������254 Change Your Account’s Public and Private Keys������������������������������������������254 CPU and Bandwidth Allocations�������������������������������������������������������������������255 Where to Go from Here�������������������������������������������������������������������������������������255 Summary����������������������������������������������������������������������������������������������������������255 Chapter 7: NEO Blockchain and Smart Contracts�����������������������������257 NEO’s High-Level Blockchain Architecture��������������������������������������������������������258 What Is NEO’s Smart Economy?������������������������������������������������������������������260 Setting Up Your Local Environment�������������������������������������������������������������������262 Xcode 10.2���������������������������������������������������������������������������������������������������263 Install Visual Studio 2017 IDE����������������������������������������������������������������������263 Install .NET Core������������������������������������������������������������������������������������������264 Download NeoCompiler and Generate neon.dll�������������������������������������������267 neo-cli to Generate a NEO Node������������������������������������������������������������������269 Create a Local NEO Private Testnet�������������������������������������������������������������������271 Python 3.6���������������������������������������������������������������������������������������������������272 Install neo-python����������������������������������������������������������������������������������������273 Install neo-privatenet-docker����������������������������������������������������������������������275 Start a Network and Claim Initial NEO and Gas�������������������������������������������275 Bootstrapping the Testnet����������������������������������������������������������������������������277 Start NEO Bash��������������������������������������������������������������������������������������������277 Potential Problems During Installation��������������������������������������������������������279 NEO “Hello, World”���������������������������������������������������������������������������������������281 Building the NeoContract Framework: Neo.SmartContract. Framework.dll���������������������������������������������������������������������������������������������282 Create a NEO “Hello, World” Project������������������������������������������������������������284 Coding the NEO “Hello, World” Smart Contract in C#����������������������������������287 Coding the NEO “Hello, World” Smart Contract in Python���������������������������288 Compiling Your Smart Contracts to .avm�����������������������������������������������������289 Publish a Smart Contract on a Private Testnet��������������������������������������������������290 Publishing to Mainnet���������������������������������������������������������������������������������������292 Bootstrapping to Mainnet����������������������������������������������������������������������������292 Installing the neo-gui Client������������������������������������������������������������������������292 Ethereum vs. EOS vs. NEO : Smart Contracts Developer Perspective Showdown�������������������������������������������������������������������������������������292 Where to Go from Here�������������������������������������������������������������������������������������297 Summary����������������������������������������������������������������������������������������������������������298 Chapter 8: Hyperledger���������������������������������������������������������������������299 Hyperledger Overview���������������������������������������������������������������������������������������300 Understanding Hyperledger Fabric�������������������������������������������������������������������304 Installing Hyperledger Fabric and Composer����������������������������������������������������308 Prerequisites�����������������������������������������������������������������������������������������������309 Installing VSCode with Hyperledger Composer Extension���������������������������313 Spinning Off a Local Hyperledger Fabric Business Network�����������������������322 Hyperledger Composer�������������������������������������������������������������������������������������325 “Hello, World” with Playground�������������������������������������������������������������������������326 Deploying a Business Network��������������������������������������������������������������������327 Business Network Archive (.bna)�����������������������������������������������������������������328 Adding the Model File����������������������������������������������������������������������������������329 Adding Chaincode����������������������������������������������������������������������������������������331 Creating an Asset����������������������������������������������������������������������������������������331 Access Control���������������������������������������������������������������������������������������������332 Testing the Model����������������������������������������������������������������������������������������333 Importing/Exporting the Model��������������������������������������������������������������������334 Playground Online���������������������������������������������������������������������������������������336 Deploying on a Local Hyperledger Fabric Network�������������������������������������������340 Running the “hello-network” Network��������������������������������������������������������������341 Starting the “hello-network” Business Network and Admin Card���������������341 Importing a Business Card��������������������������������������������������������������������������342 Where to Go from Here�������������������������������������������������������������������������������������343 Error Troubleshooting����������������������������������������������������������������������������������������344 Composer Runtime Install Error or Card Not Found������������������������������������344 Docker Unauthorized Authentication Required Error�����������������������������������345 Docker Container Conflicting Errors������������������������������������������������������������345 Mismatch and Cleanup��������������������������������������������������������������������������������346 Summary����������������������������������������������������������������������������������������������������������347 Chapter 9: Build Dapps with Angular: Part I�������������������������������������349 What Is a Dapp?������������������������������������������������������������������������������������������������350 Dapp Classification��������������������������������������������������������������������������������������352 Dapp Projects����������������������������������������������������������������������������������������������353 How Do You Create Your Own Dapp?�����������������������������������������������������������354 Why Angular?����������������������������������������������������������������������������������������������������357 Creating an Angular Dapp����������������������������������������������������������������������������359 Styling an Angular App��������������������������������������������������������������������������������376 Creating Content������������������������������������������������������������������������������������������382 Summary����������������������������������������������������������������������������������������������������������394 Chapter 10: Build Dapps with Angular: Part II����������������������������������395 Transfer a Smart Contract���������������������������������������������������������������������������������396 Create a Smart Contract������������������������������������������������������������������������������398 Create the Truffle Development Network�����������������������������������������������������400 Deploy the Smart Contract��������������������������������������������������������������������������401 Link with the Ethereum Network����������������������������������������������������������������������406 Transfer Service������������������������������������������������������������������������������������������407 Connect to MetaMask���������������������������������������������������������������������������������������413 Test Your Dapp Functionality�����������������������������������������������������������������������������417 Where to Go from Here�������������������������������������������������������������������������������������417 Summary����������������������������������������������������������������������������������������������������������418 Chapter 11: Security and Compliance����������������������������������������������419 Security and Compliance Readiness�����������������������������������������������������������������421 Security Readiness��������������������������������������������������������������������������������������421 Compliance Readiness��������������������������������������������������������������������������������423 Readiness Recommendations���������������������������������������������������������������������427 Common Blockchain Attacks����������������������������������������������������������������������������431 Wallet Cyberattacks�������������������������������������������������������������������������������������431 Blockchain Network Attacks������������������������������������������������������������������������437 Platform Attack��������������������������������������������������������������������������������������������444 Development Cycle�������������������������������������������������������������������������������������������456 Design and Coding��������������������������������������������������������������������������������������457 Discovery, Audit, and Test����������������������������������������������������������������������������457 Discovery�����������������������������������������������������������������������������������������������������458 Audit������������������������������������������������������������������������������������������������������������458 Test��������������������������������������������������������������������������������������������������������������459 Readiness Assessment��������������������������������������������������������������������������������464 Release��������������������������������������������������������������������������������������������������������465 Where to Go from Here�������������������������������������������������������������������������������������465 Summary����������������������������������������������������������������������������������������������������������466 Chapter 12: Blockchain Beyond Crypto��������������������������������������������467 Harnessing Blockchain�������������������������������������������������������������������������������������468 Coins������������������������������������������������������������������������������������������������������������469 Tokens���������������������������������������������������������������������������������������������������������470 Ledgers��������������������������������������������������������������������������������������������������������472 Smart Contracts and Dapps�������������������������������������������������������������������������473 Decentralization of Industries and Verticals������������������������������������������������������474 Financial������������������������������������������������������������������������������������������������������475 Cybersecurity����������������������������������������������������������������������������������������������478 Real Estate��������������������������������������������������������������������������������������������������481 Mobile����������������������������������������������������������������������������������������������������������483 Supply Chain������������������������������������������������������������������������������������������������485 Encrypted Messaging����������������������������������������������������������������������������������487 Elections and Voting������������������������������������������������������������������������������������487 Marketing����������������������������������������������������������������������������������������������������488 Healthcare���������������������������������������������������������������������������������������������������490 Gaming��������������������������������������������������������������������������������������������������������494 Music�����������������������������������������������������������������������������������������������������������495 Where to Go from Here�������������������������������������������������������������������������������������500 Summary����������������������������������������������������������������������������������������������������������500 Index�������������������������������������������������������������������������������������������������503 Blockchain Basics This chapter will serve as your ground school before you “take off” toward development. It will introduce basic concepts that will help you to understand the blockchain technology. This chapter is split into four parts. – Introduction to Cryptoeconomics – Blockchain Explained – Cryptocurrencies Overload – Blockchain P2P Network To understand cryptoeconomics, you first need to understand concepts such as encryption and decryption, private-public keys, cryptography, digital assets, cryptography, and cryptocurrency. Once you understand these basic concepts, I will cover blockchain. I will cover the pieces that make up an individual blockchain, such as blocks, and how the blocks are linked together, as well as the problems with blockchain such as double spending. I will also explain cryptomining, cryptominers, and cryptocurrency wallets. Then, I will cover the different types of cryptocurrencies: bitcoin, tokens, and alternative cryptocurrency coins (altcoins). Last, I will cover the P2P network that is used with the blockchain technology and the different layers that make up the network: consensus layer, miner layer, propagation layer, semantic layer, and application layer. Chapter 1 Blockchain Basics Introduction to Cryptoeconomics The world of crypto is full of technical jargon that can confuse even the savviest technology ninja. Bitcoin introduced the concept of cryptoeconomics and paved the way for the creation of many blockchain platforms. Before we dive deep into how a blockchain works, let’s understand what cryptoeconomics is and the underlying concepts behind a blockchain. Verbal communication is based on selecting words to describe a message you want to convey. However, sometimes you want to communicate with only certain people while excluding others. A good example is during wartime; a commander communicates with soldiers stationed on the front line while ensuring the enemy is unable to listen. The commander could use encryption for this communication. Electronically speaking, today all shopping sites offer their merchandise over an encryption protocol, called Secure Sockets Layer (SSL), that can protect your personal information from hackers. Video encryption and decryption are common to ensure the delivery of video to authorized members only, and on personal computers, people often use encryption to back up and protect files and passwords. Moreover, as a developer, you likely sent encrypted messages and also decrypt incoming messages with the help of libraries as all programming languages offer string encryption and decryption functions. So, let’s look at some definitions: – Encryption: Encryption is a process of converting your message into code so that only authorized parties can access it. – Decryption: Decryption is reversing the encryption process so that the message can be converted to the original message. 2 Chapter 1 Blockchain Basics – Cryptography: This is using the techniques of encryption and decryption to send and receive messages. – Cryptocurrency: This is using cryptography the same way as the earlier SSL or video example but specifically to fit the needs of a digital asset. Note A digital asset can be anything of value, such as the combination to your home safe, a secret password, a list, a message, electronic cash, a document, a photo, and so on. – Cryptoeconomics: This is the combination of cryptography and economics to provide a platform to pass digital assets. For further clarification, let’s look at these terms in more detail and apply them to the topics I will be covering in this book. Ig-pay Atin-lay To begin, let’s go back in time. Have you ever spoken as a child in Pig Latin? The secret Pig Latin language is simple. You take off the first letter of the word you want to say and then move the letter to the end of the word, as well as add the sound “ay.” For example: – “Pig” become “ig-pay.” – “Latin” becomes “atin-lay.” What we just have done is encryption. Then to understand the words we have encrypted, we need to work backward. 3 Chapter 1 Blockchain Basics – “Ig-pay” becomes “pig” by removing “ay” from the end and taking the last letter and putting it as the first letter. – Similarly, “atin-lay” becomes “Latin.” What we have just done is decryption. Children are able to use these techniques to encrypt and decrypt words in a simple form of cryptography. E ncryption/Decryption Encryption enables you to pass messages between specific parties in a secure manner so excluded parties will not understand them. Throughout history, there was a need to be able to send secret messages between parties. One party sends an encrypted message at one place, and then the other party is able to receive and decrypt the message elsewhere. In fact, encryption was used a lot during World War I (WWI) and World War II (WWII). The Nazis used a machine called Enigma to encrypt and decrypt messages (see Figure 1-1). The Allies figured out a way to break the Nazi Enigma machine’s secret code and decrypt the messages. This is believed to have shortened WWII by years. Figure 1-1.  Enigma machine. Photo credit: 4 Chapter 1 Blockchain Basics Encryption and decryption went from pure Army usage to public usage by way of the development of the Data Encryption Standard (DES) by IBM in 1970 and the invention of key cryptography in 1976. In fact, in the past, cryptography and encryption were synonymous. Encryption + Decryption = Cryptography As mentioned, cryptography is the process of using the techniques of encryption and decryption. The word cryptography came from the Greek word kryptos, which means hidden or secret. In the Pig Latin language example, I described how you can encrypt and decrypt words. That technique of removing the first letter and adding it to the end with “ay,” and then vice versa, is cryptography. Without knowledge of the technique, you wouldn’t be able to understand the Pig Latin language. Most people are probably smart enough to figure out the secret Pig Latin language as it’s simple in nature; however, a complex encryption example would be a different story. For instance, going back to the WWII Enigma machine, the Nazis were passing messages over the air. The Allies were capable of receiving these messages (the messages were the “public keys”), but without a way to decode them (the “private keys”), it was not enough. It took a scientist named Turing and others five-and-a-half months to decrypt the Nazi’s secret messages. Note A cryptographic key can be used to encrypt a message. The encrypted message can then be decrypted only by using the second key (a private key) that is known only to the recipient. 5 Chapter 1 Blockchain Basics Turing’s contribution was to automate a machine that was capable of figuring out different settings the Nazis made in their Enigma machine so they could decrypt messages In other words, it automated the process of searching for the private key. That machine was called bombe. Digital Assets + Cryptography = Cryptocurrency Cryptocurrency is a digital asset designed so that electronic cash is able to be exchanged using strong cryptography (encryption and decryption) to ensure the security of funds, transactions, and the creation of new funds. The cryptography’s private key mechanism must be strong enough that it would be almost impossible (in other words, take too much time and effort) to figure out. Otherwise, all users could potentially lose their electronic cash if the cryptography could be figured out within a few months such as with the Enigma machine. An example of cryptocurrency is bitcoin. Although bitcoin was not the first cryptocurrency invented, it’s generally considered the first successful cryptocurrency. Bitcoin’s success is attributed to the following characteristics: no one can break the public-private key, it’s distributed without a controlled government, it’s publicly available, and it’s published as open source code. Note  Bitcoin was invented in 2008 by Satoshi Nakamotoi with the publication of a white paper called “Bitcoin: A Peer-to-Peer Electronic Cash System” ( The actual complete open source software was released a year later in 2009 ( 6 Chapter 1 Blockchain Basics Cryptography + Economics = Cryptoeconomics Cryptoeconomics is the combination of cryptography and economics to provide a platform that gives an incentive to maintain the platform, its scalability, and its security; in addition, it is absent of central or local government control. In other words, it’s decentralized. The network is made up of a collection of multiple computers instead of one central computer. Note  Decentralized is the opposite of central control; it means without central or local government control. Bitcoin is able to achieve cryptoeconomics’ goals by using the private-­ public key concepts; cryptography and cryptographic hashing functions are used indirectly. In fact, the relation between cryptography and cryptocurrency is indirect not just for bitcoin but for most cryptocurrency out there. For instance, cryptography is used in bitcoin in other ways such as the following: – Bitcoin uses private keys (bitcoin calls these digital signatures) with the help of an algorithm function (called the ECDSA elliptic curve) to prove ownership. – Hashing algorithms are used for holding the structure of the database ledger data (or blockchain) via a hash generator called SHA256. – The hashing algorithms are used to generate math puzzles that a computer tries to solve for a prize. Once the puzzle is solved, the computer is selected to help handle the transactions. 7 Chapter 1 Blockchain Basics – Hashing algorithms are also used to generate account addresses. – There is the concept of Merkle trees (covered in the next chapter), which use the hashing keys of large data in small pieces. This is useful for lightweight wallets that are needed on constrained hardware devices such as mobile devices. Bitcoin does not gather identity information for its users; however, the transactions are public, meaning that all the information is transmitted and available online. Think of the Enigma example again; this means that anyone can intercept the messages transmitted. However, without the private key, no one can decrypt the messages. Since the release of bitcoin in 2009, there are many other platforms that use different types of privacy for sending information in a secure manner and that use encryption for more portions of the process so that less information is public. Platforms such as Monero and Zcash use anonymity via cryptography even for messaging a transaction’s details. Blockchain Explained As I mentioned, bitcoin was the first successful open source digital cash. Blockchain is the core technology, or the heart behind bitcoin and in fact behind all cryptocurrency platforms. But what is blockchain? In short, a blockchain is a shared digital ledger. Think of a database that instead of storing all the database entries on one computer it stores the data on multiple computers. A fancier definition would be that a blockchain is a decentralized and distributed global ledger. 8 Chapter 1 Blockchain Basics Blocks + Chain = Blockchain Each block contains records and transactions; these blocks are shared across multiple computers and should not be altered absent an agreement (consensus) of the entire network. The network is ruled according to a specific policy. The computers are connected on one network and called peers or nodes. Note  What is blockchain? A blockchain is a digital decentralized (no financial institutions involved) and distributed ledger. In layperson’s terms, it is a database that stores records and transactions on multiple computers without one controlling party and according to an agreed policy. The data that is stored is a block, and the blocks are linked (chained) together to form a blockchain. L inked Blocks A blockchain consists of a collection of data (a block) linked to the previous block. How are they linked? A block contains data, and each block references the block preceding it, so they are linked just as a chain link would be connected to the chain link before it. Take a look at Figure 1-2; as you can see, each block is referencing the previous block. 9 Chapter 1 Blockchain Basics Figure 1-2.  Blocks chained together So, a blockchain contains blocks, which hold records of transactions. The private keys are held by the owner to show proof of ownership (this is the digital signature), so no one without the private key can decrypt the string and claim ownership. This combination of public keys and private keys represents the electronic cash. Note Peers form a network of nodes, so throughout this book, you may see the word peer or node. These words are synonymous for the purpose of this book. As I said, digital assets can be anything—a music file, video file, electronic document, and so on. In cryptocurrency, a digital asset is represented as electronic cash; you can think of the public key as your bank account and routing number and the private key as the actual cash in your account. Yes, you can share your bank’s information with others, but the funds will stay in your account. To claim your cash, you need to prove ownership. You go to the bank and show a form of ID and prove it’s you by a way of signature; only then can you get your money out of your account. A similar process happens with cryptocurrency. There is a public address 10 Chapter 1 Blockchain Basics that represents your account, and only the owner holds the private key to prove ownership. Double Spending Problem A digital signature (public keys and private keys) securely ensures a party’s identity is kept private and electronic cash is stored. This concept of a private-public key combo enables you to encrypt and decrypt strings and keep a string safe, just as you saw with the Enigma machine. However, it is still not enough to solve the biggest problem of digital currency—double spending. When you use fiat money (a paper money made legal by a government) such as U.S. dollars or euros, the paper is inconvertible, which means that once you gave the paper away, you cannot spend it again. In cryptocurrency, what happens if you prove ownership and send your digital asset twice at the exact same time? This could lead to double spending. Hackers can try to reproduce digital assets as well as potentially double spend them, which cryptocurrency had to solve before it could be used as a digital currency. Note  Double spending is the risk that digital currency can be spent twice because the digital signature could be reproduced and one could prove ownership and send a digital asset twice at the same time. Blocks that hold keys are not enough to provide security and solve the double-spending potential issue to form a digital currency. Bitcoin solves this problem by creating a network of computers and proving that no attempts of double spending have occurred. This is done by having all the computers on the network aware of every transaction. All the transactions are shared with all the computers in the network. 11 Chapter 1 Blockchain Basics Double Spending Solution: P2P Network In cryptocurrency, using a peer-to-peer network provided the solution to solve the double-spending problem. Note  P2P networking is a distributed application architecture that splits the tasks that need to be performed between different peers, with each peer having the same privilege. Together the peers create a P2P network of nodes. Any computer that is connected on the network is called a peer. The peer can be any computer that meets the network requirements such as a laptop, mobile device, or server. The computers are connected to each other on the Internet via a P2P network protocol and form a network of nodes. The P2P network protocol is not new. It has been used extensively on the Web for years now, from downloading files via Kazaa or LimeWire networks to having video chats via Skype. As I mentioned, bitcoin was the first viable cryptocurrency, and it solved the double spending issue as well as allows electronic cash to be stored without going through financial institutions by utilizing P2P to form the blockchain protocol. “A purely peer-to-peer version of electronic cash would allow online payments to be sent directly from one party to another without going through a financial institution.” —Satoshi Nakamoto, Bitcoin: A Peer-to-Peer Electronic Cash System 12 Chapter 1 Blockchain Basics Cryptomining by Cryptominers As noted, each computer that holds a copy of the shared ledger and is connected to the P2P network is a peer. A peer can help to add records and verify transactions. The process is called cryptocurrency mining or cryptomining, and the peer that helps record and verify the transactions is called a cryptominer or a miner for short. Each miner helps to verify and add transactions to the blockchain digital ledger. The miners are often rewarded with a fee for the work, and to stay competitive with other miners, the miner usually needs a computer with specialized hardware. Cryptocurrency Wallet I covered what the public keys and private keys are and how they are used to encrypt and decrypt strings. The strings are digital currency or cryptocurrency, and the keys represent digital money. A cryptocurrency wallet stores one or multiple public key and private key combinations and is used to receive or spend cryptocurrency. A good analogy is to think of a wallet like your bank account. Cryptocurrency can be created by getting a reward by doing the miner work, or it can be purchased. I will expand on wallets later in the book. Cryptocurrencies Overload Before diving deeper into the blockchain P2P network, you should know that another concept that can cause confusion is the difference between coins and tokens. According to, at the time of writing, there are 1,833 listed cryptocurrencies with a market cap of $200 billion. 13 Chapter 1 Blockchain Basics Many of these coins will surely disappear in the years to come as they offer little value, and these projects will be terminated because of a lack of interest or being a scam. This can be confusing and intimidating, and most people don’t understand the concept of bitcoin, let alone the large number of coins and tokens out there. To help understand these concepts, let’s break down cryptocurrencies into three types: bitcoin, tokens, and alternative cryptocurrency coins (altcoins). See Figure 1-3. Figure 1-3.  Cryptocurrency coins and tokens. Photo credit: blog. Bitcoin Digital Cash Bitcoin was the first successful implementation of a decentralized distributed digital currency. There are 21 million coins in total. The coins replace a traditional fiat currency. 14 Chapter 1 Blockchain Basics Tokens Tokens are a decentralized product offering. It is another option similar to an initial public offering (IPO) or crowdfunding. The tokens can be created anywhere in the world and delivered via Ethereum, EOS, or another capable blockchain platform. Tokens are usually created and distributed to the public via an initial coin offering (ICO). Tokens stand for a utility or an asset that usually sits on top of a native blockchain. It can represent any digital asset including loyalty points, cryptocurrencies, or any good or commodity with individual units that are an interchangeable, fungible, or tradable asset. You can create a token using an existing blockchain template such as the Ethereum platform, or you can create your own tokens on an existing native blockchain and issue your own tokens. You can utilize smart contracts to simplify the process of creating tokens, as will be discussed in later chapters. Note Smart contracts are programmable code that runs on its own without the need for third parties. For instance, Solidity is a contact-­oriented programming language and can be deployed on multiple blockchains. Alternative Cryptocurrency Coins (Altcoins) Alternative cryptocurrency coins (altcoins for short) are coins that are derived from bitcoin core source code by forking it (soft fork or hard fork). Examples are litecoin (which was a fork of the bitcoin core client), dogecoin (dogecoin 1.10 is a complete rebuild based on the bitcoin 0.11 build), bitcoinX, bitcoin cash, and bitcoin gold. In fact, at the time of writing, there are 26 altcoins. 15 Chapter 1 Blockchain Basics Note Hard forks are backward incompatible because the changes split the network code into two—the P2P network with the original code and the new P2P network running the new code. Soft forks are backward compatible, meaning that previously valid ­blocks/transactions become invalid, and old nodes recognize new blocks as valid. This forking happens often when there is a disagreement of developers regarding a direction. For instance, some developers would like to implement changes that other developers disagree with or a major fix is needed to be implemented. Litecoin was a fork of the bitcoin’s core client. Litecoin changed the time of blocks being sent from 10 minutes to 2.5 minutes, enabling transactions to be transferred quickly and more efficiently than bitcoin. Litecoin can then continue and add features as it’s not relying on bitcoin’s code anymore. For instance, in the future, litecoin will enable atomic swap, allowing people to convert Litecoin to bitcoin via smart contracts without involving an exchange. However, changes in the bitcoin core will require manual implementation to have these changes included in litecoin. With that said, many will argue that Litecoin and many of these altcoins don’t offer enough value to survive and are made with the purpose of enriching the developers who created the fork. Only time will tell. EOS is another good example of altcoins. This time, the altcoin is turning into a token, as upon its release the EOS company issued Ethereum tokens, but as EOS is building its own blockchain platform, it is replacing the Ethereum token with its own EOS tokens. In a nutshell, the main difference between altcoins and tokens is in their structure. An altcoin is its own currency like bitcoin or Litecoin, with its own dedicated network blockchain and need for miners. Tokens such as Ethereum tokens operate on top of an existing blockchain, which provides the token and the infrastructure (such as Ethereum) for the creation of a 16 Chapter 1 Blockchain Basics decentralized application (dapp). An example of an Ethereum token is the binance token (BNB). In regard to Ethereum tokens, Ethereum offers the creation of different token standards or Ethereum Request for Comments (ERCs) such as ERC-20, ERC-223, or ERC-777. In the BNB token example, ERC-20 was used. These standards differ and will be discussed in more detail in later chapters. Blockchain P2P Network Now that you have a better understanding of the key concepts, you can dive deeper into understanding how a blockchain uses a P2P network to solve the double spending issue as well as exclude financial institutions. In this section, you will see how the cryptocurrency P2P network works. You will explore different blockchains policies specifically and the P2P network in general by breaking the P2P network into five layers. • Consensus layer • Miner layer • Propagation layer • Semantic layer • Application layer The overview here will pave the way for the next chapters where you will be utilizing the bitcoin core API to configure and run a peer. This fundamental understanding can help you understand how any blockchain network works by utilizing different policies such as NEO and EOS. 17 Chapter 1 Blockchain Basics Consensus Mechanism In a traditional centralized system such as a bank, there is a master computer that is trusted with the ledger of transactions. The bank can obviously trust its own computer, and therefore it has no problem being the one responsible for the security and integrity of the master computer. When you are dealing with untrusted peers sharing a ledger, there is a need to place rules that will ensure security and provide integrity of the ledger to prevent double spending and other potential hacker attacks. These rules and agreements are called a consensus mechanism. Note A consensus mechanism is an agreement needed for the network to operate properly even in the event of a failure. It needs to be able to achieve agreement on the data of the network within the distributed P2P network. The blockchain is not just one master computer and aims to work globally. It achieves integrity with a consensus of the data by all the computers connected on the network. A distributed consensus means that a pool of peers, geographically apart, agree in a decentralized manner, instead of one master computer (centralized). Instead of regulations, there are rules that are usually set in an open source environment instead of being set by a government entity. The P2P network enables a ledger. To achieve this goal in a secure way, the P2P network stores the digital ledger rules and security. The consensus mechanism provides not only the rules but also the incentives to do the work of storing the data and creating transactions by giving the reward to miners. The P2P network works globally using an Internet connection and is able to provide a platform to achieve a globally distributed consensus mechanism. In cryptocurrencies, the consensus/agreement is on whether 18 Chapter 1 Blockchain Basics the blocks are valid or not. If a block is valid, the block will be added to the blockchain. If a block is invalid, it will be rejected from being added to the blockchain. That’s where a consensus policy comes into play. Most of the peers in the network hold the same blocks in their validated best blockchain and follow the same rules (consensus rules); that’s how blockchain ensures security. The most difficult to re-create chain is known as the best blockchain (more about this concept later in the chapter). roof of Work, Proof of Stake, and Delegated P Proof of Stake As the blockchain gained popularity, many consensus mechanisms policies were created. The first one was created by bitcoin, and many others were built to solve problems that exist in other mechanisms. In the following sections, I will discuss a few popular ones. – Proof of work (PoW) – Proof of stake (PoS) – Delegated proof of stake (DPoS) In addition to these three, there are many other consensus mechanisms that are not covered in this book, such as proof of importance, proof of elapsed time (PoET), proof of authority (PoA), proof of burn, proof of capacity, proof of activity, and so on. Feel free to explore these on your own; each has its pros and cons and fits different needs. Proof of Work PoW is the first and most popular mechanism; it’s used by bitcoin and Ethereum, which are the most popular cryptocurrencies at the time of writing. PoW is achieved by having a network of miners and presenting the 19 Chapter 1 Blockchain Basics miners with a mathematical problem. When miners solve a problem, they are rewarded with a cryptocurrency. The reward is the proof of the “work” done, and that’s where the name comes from. Note Ethereum’s development community is looking to move from PoW to PoS or ProgPoW (reduced ASICs’ hash rate benefit mechanism). PoW determines what peer does the work by the amount of computer power (hash rate) and allocates the work as a percentage so it’s fair. PoW does not trust any peer on the network individually, but the network trusts all of them as a collective network. This does not mean that one miner competes against another miner. A network of miners (called a pool) can compete against another pool of miners for the job. The higher hash rate the pool has, the more chances it has to get the “work.” As covered previously, cryptocurrencies are decentralized and work without one trusted computer in charge of the ledger. The PoW is the mechanism that ensures data integrity and discourages malicious attacks. The proof of work (PoW) is the mathematical puzzle the miner needs to solve. A miner needs to find a solution to a complex mathematical problem to become the leader and be able to create the next best block to be added to the blockchain. The more miners that exist in the network, the more complex the mathematical difficulty that needs to be solved. For bitcoin, only one block is added every ten minutes with only one winner, so the competition is fierce. Solving a problem puts the chips in the computer to work, which consume electricity and produce heat. Think of your computer running an intensive video game that includes lots of media or your computer processing a video for production. 20 Chapter 1 Blockchain Basics You can also use this online resource, which connects to a bitcoin peer and does all sort of calculations to figure out the next difficulty: https:// This information is useful for figuring out mining profitability. At the time of writing, bitcoin shows 5 trillion as the difficulty rate, with an estimated next difficulty increase of +3.74% and a total hash rate of 43 trillion GH/s. It also shows that one block takes 9.9 minutes to create, and it generates about 25 bitcoins. A quick calculation shows that if every 10 minutes we get a block the data size of 4.2 MB per year, then 80 bytes of data per block ∗ 6 hours ∗ 24 hours ∗ 365 days = 4.2 MB of data per year. Having a block created every ten minutes is a limiting factor, and the number of transactions that can be included in each block is limited. That creates a scalability issue that other consensus mechanisms tried to improve on. To summarize, each miner is racing to solve the same problem; once the problem is solved, the process restarts. This problem is a mathematical puzzle known as the proof-of-work problem, and the reward is given to the first miner who solves the problem. Then the verified transactions are stored in the public ledger. This PoW is not without its own disadvantages; this type of algorithm can create all sorts of problems in today’s world. For instance, if one mining pool controls more than 51 percent of the total mining power, the entire blockchain security is at risk as you have one central collective not much different than having one computer. A DDOS attack against the network can put the entire trustworthiness of the network at risk. This actually happened and is not just a theory. At the time of writing, bitcoin gold, a forked version of bitcoin, has suffered a DDOS attack. A distributed denial-of-service (DDoS) attack happens when multiple systems are attacking a target’s system resource/bandwidth. 21 Chapter 1 Blockchain Basics On PoW, as the difficulty goes up, that means less profit. Less profit results in less incentive to mine coins. Ethereum cryptocurrency is facing a problem of reduced miners in the network, and in 2018 Ethereum had to plan a “difficulty bomb,” which reduced the difficulty (raising profit for miners), as well as switch from PoW to PoS to increase scalability. How is an attack is achieved? A pool that accounts for 51 percent of the network’s hashing power is able to create its own block and post it faster than the main blockchain updates. The block holds 51 percent of the network and is able to double spend coins by removing transactions after spending so that the coins are not taken from the originating wallet. This threat is real. At the time of writing, Bitmain, a mining company, controls more than 40 percent of the total bitcoin’s hash rate. Many view PoW as unsustainable and insufficient because of the amount of electricity a miner uses and the slow transaction speed compared to other algorithms. To put things in perspective, bitcoin’s current estimated annual electricity consumption is about 60 to 73 terawatt hour (TWh) per year. That’s a similar amount of electricity that it takes to power Switzerland in a year; imagine multiple coins becoming as popular as bitcoin utilizing PoW. Read more about PoW in the bitcoin white paper at https://bitcoin. org/bitcoin.pdf written by Satoshi Nakamoto. P roof of Stake PoS was created by Sunny King and Scott Nadal in 2012 as an alternative to solve the PoW cons mentioned earlier. PoS relies on how many coins a peer holds. The peer needs to stake the number of coins it wants to mine. Instead of hashing power, we have stake power, and there is no dependency on energy consumption because there is no puzzle to solve. PoS provides a similar hashing block scheme to bitcoin’s PoW, but it limits the number of peers. This provides the needed security yet lowers the cost 22 Chapter 1 Blockchain Basics and power consumption. A network fee is provided to peers instead of giving a reward for solving a mathematical puzzle as in PoW. PoS determines what peer does the work by the size of the stake the peer holds. This achieves a distributed consensus at less energy and less cost. DDOS attacks and frauds are still possible. However, attackers cannot transact more digital currency than they are staking. Otherwise, they would lose their deposits, so the chances are lower for an attack. Keep in mind that attackers can stake other people coins and won’t care to lose these coins as they are not theirs, so there are still ways for a DDOS attack. Any peer can participate in the mining process by staking coins in order to validate a new transaction. To become a miner, there are two options; you can stake your coins to be used by a trustworthy node (but you can lose your coin via a fraud of the PoS network by the node), or you can submit a full node to be selected as a miner. Decentralization is limited as only a few miners can hold most of the coins and have majority control. For the work, each miner gets selected randomly; it’s not based on solving a puzzle. Take a look at Table 1-1, which compares PoW and PoS. Table 1-1.  PoW vs. PoS Category PoW PoS Generating new blocks First miner to solve problem selected based on hashing power Random selection based on stake power (how many coins a peer holds) Reward Block reward Network fees Energy and resource ASIC miner and large consumption footprint Little resource and low energy consumption You can set a staking wallet that holds the coins you need for the PoS. Your coins can earn a return annually in some blockchain networks. 23 Chapter 1 Blockchain Basics Here is a list of some popular cryptocurrency coins that use PoS: • Dash: You need 1,000 units to be a master node. It gives an annual return of approximately 7.5 percent per year. • NEO: Staking wallets return approximately 5.5 percent per year. There’s no need to mine; you get gas coins just by holding coins. • Others: LSK, PIVX, NAV, RDD, BEAN, Linda, DCR, NEBL, OK, STRAT. Although some coins provide annual returns, keep in mind that in case the coin market cap stays stable, a single coin will be worth less over time, as new coins are generated. By staking a wallet, the hold (HODL) wallet’s value is less affected as you get more coins to maintain your wallet value. Similar to how a bank gives you an X% interest rate and the inflation is X%, your balance shows more funds, but realistically you own the same amount of money. Note HODL is a slang term coined in association with cryptocurrency to describe holding cryptocurrency disregarding price fluctuation. Let’s examine NEO as an example. You won’t need to mine NEO to get a reward. You will get gas coin just for holding coins as a reward for help with staking transactions. You can calculate how much gas coin you will receive by using this URL: At the time of writing, if you purchase five NEO coins and hold them for a year, you will get 0.4799 gas coins (currently at a price of $7.73) by placing them in staking wallets. See Figure 1-4. 24 Chapter 1 Blockchain Basics Figure 1-4. gas staking calculation I encourage you to read the white paper about PoS here: Delegated Proof of Stake Delegated proof of stake is a census algorithm method invented by Dan Larimer discussed in the white paper at Documentation/blob/master/ DPoS is aimed at improving PoS cons by providing a democracy instead of the random process of selecting a miner. Note In DPoS, the miners are called block producers. 25 Chapter 1 Blockchain Basics DPoS achieves a technological democracy by splitting the process of mining into two parts. • Election: When electing a group of block producers, there are only 21 block producers instead of unlimited as with PoW. • Scheduling production: Each one of the 21 block producers takes turns to produce a block every 3 seconds. The election process provides a technological democracy and ensures stakeholders are in control because large stakeholders have the most to lose if a network fails. Each block producer takes a turn at producing a block, and the longest possible chain gets adopted (just like in PoW). Take a look at a normal operation, as shown in Figure 1-5. You’ll see that each peer 1 through 3 gets its turn to produce the longest chain block. Anytime an honest peer node sees a valid strictly longer chain, it will switch from its current fork to the longer one. Figure 1-5.  DPoS normal operation DPoS is able to continue and function even when most of the producers fail. Figure 1-6 shows a minority fork, where peer 2 only gets to post the longest chain once during a cycle. During a fail process, the community can vote and replace a failed peer producer, in this case peer 1, or peer producers until the network resumes to normal operation. 26 Chapter 1 Blockchain Basics Figure 1-6.  DPoS minority fork This white paper describes in detail this process and how blocks are being produced and the rules to handle fail chains: dpos/@dantheman/dpos-consensus-algorithm-this-missing-white-paper. Setting a community of block producers and staked users who agree to these sets of rules gives the efficiency of PoS with the decentralized way that PoW operates. DPoS uses the power of stakeholders to approve voting of the consensus algorithm rules such as incentive fees, block intervals, forks, and transaction sizes. These rules can be fine-tuned by the elected delegates. This type of consensus can decrease the transaction time significantly (1 second versus 10 minutes for PoW). Further, the consensus protocol is designed to protect all the participants against unwanted interference of a group of nodes as possible in POW. Examples of popular DPOS blockchains are Bitshares, Steem, and EOS. M ining Layer What the miners are doing behind the scenes on networks could be described as competition to do the blockchain’s work, which is really doing the network bookkeeping. For bitcoin and most coins out there that utilize PoW, each peer needs to hold the entire public ledger, which holds a record of all the transactions that were ever conducted. PoW miners are based on computing power and pools, while other networks take into account other considerations. For bitcoin, transactions must be validated by the miners who check the ledger, ensure the sender is not transferring funds it doesn’t have, and 27 Chapter 1 Blockchain Basics only then add the transaction to the ledger. Finally, to ensure protection from hackers, the miners seal these transactions behind multiple layers of computational work, requiring too much work for a hacker to possibly achieve. This service is rewarded by providing bitcoins as a fee to the miner. For bitcoin, the size of each batch of coins drops by half about every four years; around 2140 (unless a faster calculation than SHA2 is discovered), it will be cut to zero, and the total number of bitcoins in circulation will be 21 million. Propagation Layer The propagation layer is responsible for deciding how the shared ledger and the blocks are transmitted on the P2P network. This layer is described in detail in the blockchain white papers. Each of the peers can transmit a new transaction to other nodes on the network. This architecture allows nodes to communicate indirectly. For instance, you can send a transaction affecting two wallets without each wallet being connected directly to each other. Any node that receives a valid transaction it has not seen before will immediately forward it to all other nodes to which it is connected. This is a propagation technique known as flooding. Thus, the transaction rapidly propagates out across the P2P network, reaching a large percentage of the nodes within seconds. Semantic Layer The semantic layer takes care of how new blocks relate to previous blocks and provides the protocol for verifying the consensus rules. As you have seen, there are different types of consensus mechanisms based on how many trusted machines are connected, staking, speed, hashing power, and more, but they do work similarly to how new blocks 28 Chapter 1 Blockchain Basics are related with previous blocks to ensure security. Every blockchain has specifications. In this layer, transactions happen where coins/tokens are transferred between accounts. I discussed the best block chain and how each block contains data, and a chain of blocks has each block referencing the block preceding it. The consensus in the blockchain holds the same blocks in their validated best block chain and follows the same rules (consensus rules). That’s how a blockchain ensures security. Application Layer This layer takes care of deploying applications on top of the blockchain. For instance, dapps, smart contracts, exchanges, and sites that provide information about a blockchain are applications built on top of blockchains. For the application layer, the blockchain needs to expose APIs. Different blockchains are similar as they all provide a way for a client to communicate with the network. Bitcoin offers a full node, which is currently about 27 GB and includes a fully enforced node and all the rules of the blockchain. That is needed for mining as well as ensuring the peer you run that gets connected to the application layer is synced with the latest blocks. These full nodes contribute to the functionality of the P2P network and help support the network and its security. It’s common for a blockchain to also offer a “light” node version. In fact, the bitcoin light client is referencing a trusted full node’s copy of the blockchain. The light client allows users to interact with the bitcoin’s blockchain and makes and confirms transactions without committing the large 27 GB disk space, which helps less capable devices such as mobile. It’s important to understand that a light client is trustworthy and does not include all the consensus rules. A full node is trustless and will reject blocks that violate consensus rules, even if all the other nodes on the network recognize the transaction as valid. 29 Chapter 1 Blockchain Basics I used NEO as an example of a popular PoS blockchain. NEO also provides NEO-CLI, which includes an API that supports a consensus function that can be used for the application layer. Similarly, EOS delegated proof of stake provides a full-node and light-node option. You will start noticing that although there are many blockchain options out there, there are many similarities in the way the blockchain is implemented. Summary In this chapter, I laid the foundations and explained basic concepts regarding blockchain; I explained concepts such as encryption and decryption, cryptography, digital assets, cryptography, and cryptocurrency. I covered the pieces that make up a blockchain, including blocks, double spending, cryptocurrency, cryptomining, cryptominers, and cryptocurrency wallets. I covered different types of cryptocurrencies: bitcoin, tokens, and altcoins. Lastly, I covered the blockchain P2P network and the different layers that make up the network: consensus layer, miner layer, propagation layer, semantic layer, and application layer. You also learned about the peer-to-­ peer network core logic and proof of work (PoW), proof of stake (PoS), and delegated proof of stake blockchain (DPOS). In this chapter, I introduced many terms that will be useful throughout this book such as digital asset, public and private keys, decentralized, double spending, smart contracts, and HODL. In the next chapter, you will install and learn about the bitcoin core API as well as learn how to create a full peer in different blockchains. This will enable you to access the blockchain P2P network and even be able to understand and create peers that can act as miners. 30 Blockchain Nodes In the previous chapter, I covered basic concepts related to blockchain and the pieces that make up an individual blockchain. I covered how blockchain technology solved the double spending problem by utilizing a P2P network, which led to the creation of a global distributed shared ledger and digital cash. The blockchain P2P network is stitched together by connecting multiple nodes, and in this chapter, you will be taking a closer look at the nodes that make up the network. The nodes or peers are machines that maintain the transactions and records on the blockchain network. Each cryptocurrency has its own blockchain and nodes; however, I will cover how to install three different blockchains that utilize different consensus mechanisms. In addition, I will cover how to interact with a node. I will be using the bitcoin core API as an example so you will have a better understanding of the ledger, blocks, transactions, and wallets. These concepts will continue to lay out the foundations and basic concepts that are needed in the next chapters. Running a Blockchain Node As we mentioned, the blockchain P2P network consists of peers that store a full copy of all the blocks in the network, which is the shared ledger. Each blockchain validates blocks via a specific consensus mechanism and is able to reject blocks that do not conform with the set of rules agreed on by Chapter 2 Blockchain Nodes the network. To be able to connect to blocks and execute commands, you need to have a peer connected to the blockchain. In this chapter, you will be setting up a full node and will learn how to get rewarded for helping the network; therefore, you will fully understand how the nodes on different networks operate. You will be creating nodes for the following: bitcoin, NEO, and EOS. Because blockchain technologies operate on different consensus mechanisms, they also have different names for the node capable of managing the blockchain. – For bitcoin, a node that can create blocks is called a miner. – For NEO, a node that has management rights is called a bookkeeping node. – For EOS, a node running the underlying network layer and able to process all transactions is called a block producer. The reason I selected these blockchains is so you can examine how different peers working on different networks with different consensus mechanism operate. Once you are able to work with different blockchains, you will start noticing a pattern and be well rounded in blockchain technology. Create a Bitcoin Miner In this section, you will turn your own computer into a bitcoin cryptominer and start cryptomining. Before doing that, you need to understand that the hashing power of your computer is not going to generate enough hash power for the mining of bitcoin to be profitable. Nevertheless, it will allow you to fully understand the full cycle, and you may be able to find other coins where mining using your CPU/GPU is profitable such as ETN, BCN, XMR, and ETH. The process is similar in all PoW-based networks. 32 Chapter 2 Blockchain Nodes Today, for a miner to be profitable, it’s a matter of hash rate and power consumption, price of electricity, bitcoin puzzle difficulty rate, and maintenance costs as well as other factors. Note  Hash rate is the number of calculations in a second that your computer can perform trying to solve the mathematical puzzle. In the early days of bitcoin, your desktop could use your central processing unit (CPU) or graphics processing unit (GPU) for processing bitcoin, and it would have been enough for bitcoin mining to be profitable. Your computer would have been able to support the bitcoin network; however, the competition has increased, and you now need a field programmable gate array (FPGA) or application-specific integrated circuit (ASIC) miner to be profitable. What are ASIC and FPGA miners? An FPGA is an integrated circuit that is able to be configured after being built. The miners have better performance than CPUs and GPUs mining; they can hash 750 megahashes per second. ASICs are computers that have an integrated circuit dedicated to performing the single task of mining instead of operating as a regular computer. There is nothing more on that computer; everything else was stripped out. This makes the computer much faster and more efficient in processing transactions, and it is able to hash more. At the time of writing, there are ASICs that can hash over 56 TH/sec, and they use less power than older generation ASCIs. This type of mining equipment is not only unique to bitcoin; at the time of writing, there are ASIC miners for other cryptocurrency such as litecoin, zCash, ethereum, and others. To get started, you first need mining software. There is a lot of mining software to choose from. For instance macOS users can, this one is free, open source, and easy to use: 33 Chapter 2 Blockchain Nodes Once you have downloaded the software, install it. Next, you need to join a mining pool. Here I’ll show how to connect to Antpool, the largest bitcoin pool; however, any pool would work. Sign up on Antpool here: Antpool calls a miner a worker. You can create a worker by clicking the Dashboard tab, then clicking the Worker link, and finally clicking Create Worker, as shown in Figure 2-1. Figure 2-1.  Antpool dashboard page for creating a mining worker Now that you have your worker ready, you will set up your miner as a CPU miner utilizing your CPU, and for your GPU, you could set your miner to utilize your graphics card. Open the MacMiner software you downloaded and click File and then Preference option from the File drop menu. In the Preferences section, set the miner as a CPU and/or GPU miner, as shown in Figure 2-2. 34 Chapter 2 Blockchain Nodes Figure 2-2.  MacMiner preferences In the next step of the preferences, you set the pool URL and your username. Antpool is set up without a password, so it’s not needed, and the pool URL is listed on the Antpool site: startum+tcp:// See Figure 2-3. Figure 2-3.  MacMiner Preferences window for setting up a miner pool 35 Chapter 2 Blockchain Nodes That’s it. Click the Start button to start mining and click Stop to stop mining, as shown in Figure 2-4. Figure 2-4.  MacMiner starting a miner Six years ago, you would have been able to mine more than 100 BTC on your GPU. As you can see, my mining power on my 2018 MacBook resulted in 13.74 Mh (Mega hashes) of hashing power. There are many resources online to help you calculate mining profitability; try As expected and according to their calculation, it would not be profitable at the current conditions. Create a NEO Bookkeeping Node Previously I introduced NEO as an example of a popular PoS blockchain. In this section, you will be setting up a node (NEO calls these bookkeeping nodes) and getting the machine ready so it can be selected to help manage the network and receive a transaction reward. 36 Chapter 2 Blockchain Nodes Note NEO does not call its managing node a miner. A miner can be an analogy for the hard work that nodes do to maintain a PoWbased blockchain. As NEO uses the PoS census algorithm and uses a technological democracy to selecting the managing nodes, there is no hashing power and no hard labor when using the PoW census algorithm. To better understand how Neo node works, it is recommended to read the NEO white paper at https://github. com/neo-project/docs/blob/master/en-us/ The node validates the blockchain blocks and pays in a cryptocurrency coin called gas. To be selected, you need to set a full node on a capable machine. The minimum required machine is listed on the NEO project wiki at­project/neo/wiki/Bookkeeping-NodeDeployment. Next, you need to obtain a consensus authority certificate and get staking gas to be nominated as a bookkeeping node. Note  You may need to be a Chinese citizen and set up a Chinese business to receive an identification certificate; see the NEO docs at You also need 1,000 staking gas to be nominated as a bookkeeping node. To receive a fee from supporting the NEO network, you will need to create a full node by following these steps: 1. Set up a full NEO node. 2. Request a consensus authority certificate. 3. Stake 1,000 gas. 4. Be elected by NEO holders. 37 Chapter 2 Blockchain Nodes To set up a full NEO node, you also need to meet the system minimum requirement listed here:­project/neo/wiki/ Bookkeeping-Node-Deployment. Setting Up a NEO Node on AWS Ubuntu As my computer does not meet the minimum requirement list, I will be utilizing AWS to set up a full node. However, if you have a machine that meets these requirements, feel free to skip using Amazon AWS or select another service provider to set your Node. For AWS, go to the following URL: Select “Create free account” and sign up. Once you complete the sign-up process, select the free Basic Plan. Then sign into the console at com/console/home and select “Launch a virtual machine.” In the first step, you can select the machine type. Select Ubuntu. “On the Step 1, wizard page: Choose an Amazon Machine Image (AMI)” ➤ Next, select: Ubuntu Server 16.04 LTS (HVM), SSD Volume Type ➤ Click the “select” button. See Figure 2-5. Figure 2-5.  AWS, selecting Ubuntu Server 16.04 LTS 38 Chapter 2 Blockchain Nodes On the next screen, select General purpose – t2.micro – free tier eligible check-box. See Figure 2-6. Figure 2-6.  AWS, selecting t2.micro machine On the next screen, you will be prompted to create key pairs: Select “create a new key pair” ➤ next, select “key pair name” ➤ call the key “neo” ➤ then download the key: “download key pair” ➤ Lastly, select “Launch Instances.” See Figure 2-7. Make sure you download the key, as you won’t be able to connect via SSH to the box without the key. Note Secure Shell (SSH) uses port 22 to connect your computer to another computer on the Internet. 39 Chapter 2 Blockchain Nodes Figure 2-7.  AWS key pairs Next, you will get a message, with a link: your instances are now launching. The following instance launches have been initiated: [instance id]. Click the link and you will be able to view the instance, as shown in Figure 2-8. Figure 2-8.  AWS, launching an instance In the instance, you will find a link to the security settings. Scroll to the right of the screen, or go to the top-left navigation bar, and select Network & Security ➤ Security Groups. You will be able to change the security settings. 40 Chapter 2 Blockchain Nodes For HTTP and SSH, you want to open the port to the world (, but SSH limits you to your own computer, called My IP. See Figure 2-9. Figure 2-9.  AWS inbound security rules Next, you can create an SSH shortcut to access the server via one command, as shown here: > mkdir ~/.ssh > vim ~/.ssh/config Paste the following into the config file: Host NEO HostName [ip address] User ubuntu IdentityFile /[location of key]/neo.pem Configure these settings with the IP address of the machine and with the location of your key. Next set the permissions for the key. > chmod 400 /[location of key]/neo.pem Now, you can access your machine with one command, as shown in Figure 2-10. > ssh NEO 41 Chapter 2 Blockchain Nodes Figure 2-10.  Connecting to an AWS machine via SSH If you run into any problems connecting to the machine, use the AWS Troubleshooting page, which you can find at com/AWSEC2/latest/UserGuide/TroubleshootingInstancesConnecting. html#TroubleshootingInstancesConnectingMindTerm. Installing Bookkeeping-Node-Deployment on Ubuntu 16.04 Now that you have a machine to fit the minimum needs of a full node, you can install the software needed. Start by installing dependencies, as shown here: > sudo sh -c ‘echo “deb [arch=amd64] https://apt-mo. trusty main” > /etc/ apt/sources.list.d/dotnetdev.list’ 42 Chapter 2 Blockchain Nodes > sudo apt-key adv -keyserver -recv-keys 417A0893 > sudo apt-get update > sudo apt-get install dotnet-dev-1.0.4 It appears that the current installation instructions in the NEO docs produce errors during installation, as shown here: Depends:, The workaround is to install a different dotnet core environment sources list and update; then you will be able to install the dotnet-dev-1.0.4 core environment. > sudo sh -c ‘echo “deb [arch=amd64] https://apt-mo. xenial main” > /etc/apt/sources.list.d/dotnetdev.list’ > sudo apt-key adv -keyserver hkp:// -recv-keys 417A0893 > sudo apt-get update Remember to change the sources list back to the following: > sudo sh -c ‘echo “deb [arch=amd64] https://apt-mo. trusty main” > /etc/apt/sources.list.d/dotnetdev.list’ Now that the dotnet core environment is installed, check whether the dotnet core environment is successfully installed with the following command: > mkdir hwapp > cd hwapp > dotnet new xunit -framework netcoreapp1.1 43 Chapter 2 > > > > Blockchain Nodes dotnet restore hwapp.csproj dotnet run cd .. rm -rf hwapp/ Bookkeeping Node Deployment Now that you have the dotnet core environment installed, you can install additional dependencies and check out the NEO project. > sudo apt-get install libleveldb-dev sqlite3 libsqlite3-dev libunwind8-dev > git clone > git branch -a > git checkout v3.0 > git checkout head To run the NEO node, you will need version 1.1.2 of .NET Core. Download the SDK binary; for Ubuntu 16.4, the commands are listed here: ubuntu16-04/sdk-2.1.300. Next, run the dpkg package manager to install the package: > wget -q packages-microsoft-prod.deb > sudo dpkg -i packages-microsoft-prod.deb Now you can restore the NEO build and compile, as shown here: > dotnet restore > dotnet publish -c Release Once you compile the code, you get the location of the DLLs. neo-cli -> /home/ubuntu/neo-cli/neo-cli/bin/Release/ netcoreapp2.0/neo-cli.dll . 44 Chapter 2 Blockchain Nodes neo-cli -> /home/ubuntu/neo-cli/neo-cli/bin/Release/ netcoreapp2.0/publish/ Run the full node: > dotnet /home/ubuntu/neo-cli/neo-cli/bin/Release/ netcoreapp2.0/neo-cli.dll . This command opens a terminal command call “neo” with the version. NEO-CLI Version: In the neo terminal, you can query the version to ensure it’s working correctly. neo> show state You can also create a wallet. neo> create wallet wallet.db3 This command will request a password. password: [select a password] password: [select a passwrod] Then it generates a public key and address for your wallet. address: AXZmWZckF55xb1p566No2qh19uj8vt5d2R pubkey: 03b80edc66c9324077c8c1c4bbad1e1ace7e1b7e8ac63945a3 b5bb9f642f4520f1 You now have a NEO node on an AWS machine, and you are able to interact with the NEO command-line interface (CLI). In the next chapters, you will be interacting with the CLI. Feel free to get a head start and review the documentation for smart contracts and dapp development at the NEO site here: ­ 45 Chapter 2 Blockchain Nodes Request Consensus Authority Certificate Now that you have a working node on a qualified Ubuntu server, you can obtain a consensus authority certificate. The NEO white paper discusses the need to have an actual real identity: “DBFT combines digital identity technology, meaning the bookkeepers can be a real name of the individual or institution. Thus, it is possible to freeze, revoke, inherit, retrieve, and affect judicial decisions on them. This facilitates the registration of compliant financial assets in the NEO network. The NEO network plans to support such operations when necessary.” You can obtain CA certificates from OnChain/Neo directly. Additionally, you can find more information on the NEO forums: https:// This process is beyond the scope of this book, but it’s needed in order to be selected as a node. G etting Gas To be selected as a node, you also need 1,000 gas to stake in order to become a bookkeeper. The easiest way to purchase gas is on exchanges. The other option is to hold NEO, and you will get 0.33 gas per 1,000. See Figure 2-11 shows a button to claim gas coins once you hold NEO coins. 46 Chapter 2 Blockchain Nodes Figure 2-11. provides a Claim Gas option A simple calculation of prices of NEO and gas at the time of writing shows it’s a large investment. E lected as a Bookkeeper NEO is an electronic democracy, and NEO holders can vote on who should be a bookkeeper. At the time of writing, the NEO team has not implemented the voting features; however, they are likely to be implemented in the near future as the GitHub wiki shows a payment structure with fees, including 10 gas for voting a bookkeeper: https://­Protocol. For now, stop the EC2 node so you won’t be charged. 47 Chapter 2 Blockchain Nodes To stop the instance, select EC2 Dashboard ➤ Running instances ➤ Actions ➤ Instance State ➤ Stop. See Figure 2-12. Figure 2-12.  AWS, stop instance action Tip Amazon can charge storage fees for the EBS volumes attached to a stopped instance. The cost is five cents per gigabyte. Amazon provides one year for free. To completely avoid being charged, you need to “terminate” the instance instead of just stopping it. You can make sure you are not charged at this URL: https://console. 48 Chapter 2 Blockchain Nodes Create an EOS Block Producer You will now learn how to run a full EOS node on a dedicated server; you just need to make sure you meet the minimum hardware requirement. The requirements are listed here: eosio-nodeos/docs/install-nodeos. At the time of writing, the system requirements on all platforms are as follows: • 7 GB RAM free required • 20 GB of available storage You will learn how to set up an Ubuntu server. I will be using AWS. In AWS, select Ubuntu Server 16.04 LTS (HVM), SSD Volume Type ➤ Choose an Instance Type ➤ General purpose ➤ t2.large. This type of machine has 8 GB RAM free. An EOS node needs at least 20 GB of a storage space, so you’ll set this machine to 25 GB to be safe. To do that, select Configure Instance Detail. Next select: add storage. In the next window select: Size (GiB) 25 GB. The next wizard window you will be able to: Review and Launch. Launch the instance. For security, set the same settings as you did for the NEO full-node server: select an existing security group. Next, select: launch-wizard-1 that includes port 22 for SSH and public HTTP/HTTPS. Now we can: Review and Launch in the next window and lastly, Launch. In the key pairs, use the same key you created for NEO or create a new key. To select the same key, select Choose an existing key pair. We will call the key: EOS. That’s it. You can now update the SSH config file with the new server to be able to connect quickly. > vim ~/.ssh/config 49 Chapter 2 Blockchain Nodes And paste the following: Host EOS HostName [ip address] User ubuntu IdentityFile /[location of key]/EOS.pem Now you can connect to the EOS server. > ssh EOS Installing an EOS Full Node Now that you have the Ubuntu server configured with 8 GB of memory and a 25 GB hard drive, you can clone the project and build. > git clone -recursive > cd eos > ./ #takes about 30 mins to an hour. Once the build is completed, you will see the screen shown in Figure 2-13. Figure 2-13.  EOS full-node build, complete output 50 Chapter 2 Blockchain Nodes Ensure that the daemon is working correctly by running the -h flag to get a list of commands. > cd build/programs/nodeos > ./nodeos -h #list of commands Now you can run the EOS node daemon; Figure 2-14 shows the output. > ./nodeos -e -p eosio -plugin eosio::chain_api_plugin -plugin eosio::history_api_plugin Figure 2-14.  EOS full node running EOS provides a portal at to get started with nodes, dapps, smart contract, tokens, and much more. In the next chapters, you will be interacting more with the EOS platform. M arketing and Listing Now that you have an EOS node running, you need to create a marketing campaign to be elected. You can set the submission profile to be similar to this URL: Next, you are ready to receive votes. You can get voting through the imToken 2.0 app (iPhone or Android). It offers block producers voting; follow this guide for instructions:­141983f9a76e. 51 Chapter 2 Blockchain Nodes Terminating an EOS Node You want to ensure that you terminate the node so you won’t get charged, as this machine configuration is not part of the free tier server on Amazon. Just you did before, select EC2 Dashboard ➤ Running instances ➤ Actions ➤ Instance State ➤ Terminate. You’ll also want to terminate the 25 GB volume you created. Select Volume from the left navigation menu and then select Actions ➤ Detach Volume. Then select Delete Volume. See Figure 2-15. Figure 2-15.  Detaching a volume and deleting a volume Bitcoin Core API As a developer, you want to have deep understanding of how a technology works, so to better understand blockchain in general and the bitcoin blockchain specifically, you will be downloading and installing the bitcoin 52 Chapter 2 Blockchain Nodes core code. The full node and the bitcoin miner you set up previously on bitcoin core can be compiled from source code, or you can use a precompiled executable. Previously you set up a bitcoin node capable of doing mining on your computer. To interact with the bitcoin core API, you need a full node. What is the difference between a full node and a miner then? A full node is a complete copy of the blockchain that is able to verify all the transactions that ever occurred on the blockchain since the first block was created. This requires 180 GB at the time of writing. However, as you will see, you can set the full node not to download the entire ledger. A full node does not need to solve any mathematical problem, and hashing is not an issue. A miner is a node in the network; however, as you have seen, its job is to generate blocks by working on transactions and coming up with the best block (or hash) to store the information. Miners compete and spend about 10 minutes coming up with a solution to the problem. Full nodes keep blocks forever in the database and are verified by other nodes. Miners, on the other hand, don’t need to know about previous blocks, just the block before, and they focus on hashing. However, a bitcoin miner does download the entire 180 GB blockchain ledger. In the following exercise, you will be installing and configuring a full node to be able to connect and interact with the bitcoin core API. INSTALLING AND CONFIGURATING A FULL BITCOIN NODE Setting Up Your System In this exercise, you will set up your environment and then download, configure, and start a full working node of bitcoin. This will come in handy as you continue to examine how bitcoin and blockchain work. You will be using the bitcoin core source code. Bitcoin core code includes docs that give complete instructions for installing the code on different OSs. In this book, I am focusing on macOS, so I am providing instructions to expedite the installation 53 Chapter 2 Blockchain Nodes process for your convenience; however, you can install bitcoin core on other platforms. Here is the link for the complete instructions for Mac and PC: • macOS install instructions: bitcoin/blob/master/doc/ • Windows: master/doc/ To get started, you need Xcode and the Xcode tools installed, so this would be a good time to install these tools if you don’t have them already. To check whether Xcode is installed on your computer, open a command-line terminal by clicking the Spotlight Search and type Terminal. At the command line, type the following command to check whether you have Xcode installed: > xcode-select -v It should return xcode-select and the version number, as shown in Figure 2-16. Figure 2-16.  Terminal xcode-select version If you don’t have Xcode installed, you can download it from https:// Note This installation can take hours, depending on your Internet connection. 54 Chapter 2 Blockchain Nodes Now that you have Xcode downloaded, execute the command-line tools for Xcode. > xcode-select -install With command-line tools installed, you can install Homebrew and the wget tools by using these commands: > /usr/bin/ruby -e “$(curl -fsSL https://raw.githubusercontent. com/Homebrew/install/master/install)” > brew install wget After Homebrew and wget are installed, you are able to install the rest of the needed dependencies for bitcoin core, as shown here: > brew install automake berkeley-db4 libtool boost miniupnpc openssl pkg-config protobuf python qt libevent qrencode librsvg Installing Bitcoin Core At this point you have the needed tools and dependencies installed, and you can clone the bitcoin code project, compile, and run it. > git clone > cd bitcoin/ Now, you can build the Berkeley DB version 4, used by the bitcoin core node: > ./contrib/ . Continue the installation; > ./ > ./configure > make > make check && sudo make install 55 Chapter 2 Blockchain Nodes Bitcoin core code includes two tools: bitcoind and bitcoin-CLI. • bitcoind (the bitcoin daemon): This implements the bitcoin protocol for remote procedure call (RPC) use. Once it’s installed, you can make API calls. There is a list of all the API calls here: client/API_Calls_list. • bitcoin-CLI (the bitcoin command-line interface): This enables you to interact with the bitcoin core daemon. To ensure the installation went well, you can check that the bitcoin daemon and bitcoin-CLI are configured and working as expected. To ensure these tools were installed correctly, you can execute the which command on these tools to get the location of them. > which bitcoind > which bitcoin-cli The output returns the location of the bitcoind and bitcoin-cli: /usr/local/bin/bitcoind /usr/local/bin/bitcoin-cli Configuring and Compiling Bitcoin Core Next, you want to configure a node. Each bitcoin core node does not do mining but contributes to the bitcoin network and consists of clients, miners, wallets, and so on. To configure the node, you can find the configuration files’ location by typing the following command in Terminal: > bitcoind -printtoconsole After a few seconds, stop this service (Control+C). The command shows the bitcoin.conf configuration file location. See Figure 2-17 for the output. “> Using config file /[path]/.bitcoin/bitcoin.conf” 56 Chapter 2 Blockchain Nodes Figure 2-17.  bitcoin.conf file location At the time of writing, a full-index bitcoin core node requires 2 GB RAM and at least 180 GB of disk space ( blocks-size). Additionally, as the bitcoin nodes send and receive transactions and blocks constantly, you will need a fast internet connection. The full node is advisable for a working project running a miner as you can run a dedicated server and interact with the bitcoind via Bitcoin-­CLI; however, for the purpose of this book, most of the time you won’t need a full node. I recommend that you constrain bitcoin node resources usage on your computer so it won’t hog your computer’s resources and Internet bandwidth. To limit your node from downloading the entire shared ledger, use vim or your favorite editor to edit the bitcoin.conf file. > vim /[path]/.bitcoin/bitcoin.conf After vim opens up bitcoin.conf, paste the following configurations: “Alert: %s” prune=3000 maxconnections=10 dbcache=150 maxmempool=100 maxsendbuffer=500 maxreceivebuffer=2000 txindex=0 57 Chapter 2 Blockchain Nodes Make sure you don’t erase the following lines already there: rpcuser=bitcoinrpcrpc password=[password] For your knowledge, the configuration file holds the following params: • prune: Utilizing prune, you can limit the disk usage. Set this to 3000. • Maxconnections: By setting a limited maxconnections value, you are limiting the maximum nodes number to ten connections • dbcache: In dbcache, you reduce the size of the UTXO cache from 300 MiB to 100 MiB. • Maxsendbuffer and maxreceivebuffer: You can limit the memory buffer per connection to the number you set; for instance, set maxreceivebuffer to 2000 MB. • Txindex: Set this to 1 to get transaction data for any transaction on the blockchain; however, this will use up more disk space. Running Bitcoin Core Daemon Now that you have configured your node, you can start the bitcoin core daemon. To run the bitcoind, execute the following command in Terminal: > bitcoind -printtoconsole The first time running the daemon, it will download the blockchain. This can take several hours (depending on your Internet connection). Because you set the parameter to print to the console (-printtoconsole), you will be able to watch the process as it downloads the entire blockchain. See Figure 2-18. 58 Chapter 2 Blockchain Nodes Figure 2-18.  Bitcoin core daemon (bitcoind) While the process is running, open a second Terminal window to query the bitcoind interact with the APIs via the bitcoin-cli. Note: you can call the help feature and get help about the available APIs. For instance, to get a list of all available APIs, use this: > bitcoin-cli -help # outputs list of command-line options. > bitcoin-cli help # outputs list of RPC commands when the daemon is running. > bitcoin-cli help getblockhash # get help on specific API, for instance “getblockhash”; To be able to retrieve the complete information, you would need to run a full node. To run a full node in the config file, change txindex=1 in the bitcoin.conf file and remove prune=3000. Open bitcoin.conf using your favorite editor. > vim /[path]/.bitcoin/bitcoin.conf Change the params as follows: txindex=1 # prune=3000 – comment out this line 59 Chapter 2 Blockchain Nodes This change will allow you to run a full node and provide the index information so you can review transaction data for any transaction on the blockchain. Now you can start the bitcoin core daemon again and tell the daemon to re-index all the data. > bitcoind -reindex -printtoconsole Once again, this process can take hours; however, as it is downloading the blocks, you will be able to interact with the downloaded blocks. To get the blockchain information, you can query the daemon to show the progress of your node. See the expected output in Figure 2-19. > bitcoin-cli getblockchaininfo Figure 2-19.  Getting blockchain information 60 Chapter 2 Blockchain Nodes This did not complete the full download of the bitcoin node; however, you already have 209,513 blocks and 538,726 block headers. The node first downloads the block headers of the best chain blocks and then downloads the full blocks. In this exercise, you set your environment and downloaded blocks, configured them, and started a bitcoin node. Serialized Blocks Each full node holds the same validated blocks and follows the same rules (consensus rules). Each bitcoin block in the chain contains a 1 MB serialized code according to the current bitcoin consensus rules. The block header holds encoded information that includes the following: • Version • Previous block header • Merkle root hash • Time • nBits • nounce • txn_count (holds the total number of transactions) • txns (raw transaction) This data is being hashed and is part of the proof-of-work algorithm and the consensus rules. The Satoshi Nakamoto white paper explains the consensus rules. 61 Chapter 2 Blockchain Nodes “They vote with their CPU power, expressing their acceptance of valid blocks by working on extending them and rejecting invalid blocks by refusing to work on them. Any needed rules and incentives can be enforced with this consensus mechanism.” —Bitcoin: A Peer-to-Peer Electronic Cash System. The proof of work (PoW) in bitcoin is based on Adam Back’s Hashcash. Each miner is racing to solve the problem; once the problem is solved, the process restarts. The problem is a mathematical puzzle known as a proofof-work problem, and the reward is given to the first miner who solves the problem. Then the verified transactions are stored in the public ledger. You’ll learn more about this in the next section. It takes 9.9 minutes to generate about 25 bitcoins. Per the Satoshi white paper: “A block header with no transactions would be about 80 bytes. If we suppose blocks are generated every 10 minutes, 80 bytes ∗ 6 ∗ 24 ∗ 365 = 4.2MB per year” —Bitcoin: A Peer-to-Peer Electronic Cash System. At the time of writing, bitcoin processes three transactions per seconds, and if the bitcoin transactions increase to four transactions per second, then bitcoin will be operating at peak capacity. Ethereum, on the other hand, is running five transactions per seconds, and if it goes to eight, that would be peak capacity. This design creates a scalability flaw as large corporations need to process hundreds of thousands of transactions per seconds not just four to eight per second. 62 Chapter 2 Blockchain Nodes Block Header As mentioned, a block is shared between nodes on the bitcoin network. Each block header is a serialized 80-byte format. The following information is encoded in each block header: • Version: At the time of writing, there are four block versions. Version 1 is the genesis block (2009), and version 2 was a soft fork in bitcoin core 0.7.0 (2012). Version 3 blocks were a soft fork in bitcoin core 0.10.0 (2015). Version 4 blocks are BIP65 in bitcoin core 0.11.2 (2015). Note  What is BIP? BIP is a bitcoin improvement proposal (BIP). It is a document for introducing features or information to bitcoin. BIP is the standard for communicating ideas as bitcoin is open source and has no formal structure. • Previous block header hash: This is an SHA256(SHA256()) hash of the previous block’s header. This ensures integrity because changing one previous block will require changing each previous block. • Merkle root hash: A Merkle tree is a binary tree that holds all the hashed pairs of the tree. • Time: This is a Unix epoch time when the miner started hashing the header. • nBits: nBits is the target section of the block header. • nonce: This is an arbitrary number that miners change to modify the header hash in order to produce a hash that is less than or equal to the target threshold. 63 Chapter 2 Blockchain Nodes You already downloaded a portion of the blockchain, and you are able to query the block height already downloaded. > bitcoin-cli getblockhash 375617 The daemon returned a string with the block hash of the best block chain at index 375617. You can then request to get the actual block. > bitcoin-cli getblock 00000000000000000f270563d7f2187beec75 cdc04f98823572e5a31baf0a261 Figure 2-20 shows the results. As you can see, the block information includes the previousblockhash key and the nextblockhas key. These keys are SHA256(SHA256()) hash-encrypted keys. The rules ensure blocks cannot be changed. These rules are part of the consensus rules that are set to maintain the blockchain security by untrusted nodes. Figure 2-20.  Getting block information 64 Chapter 2 Blockchain Nodes B lock Version The block version is part of the block header. You can see the block versions used in the block. In Figure 2-20 you can see that only version 1 is used for block 00000000000000000f270563d7f2187beec75cdc04f9882 3572e5a31baf0a261. The consensus mechanism can only be changed by the bitcoin open source development team, which published instructions on how to handle upgrades suggestions. The BIP that introduced the upgrade method to handle the path for versioned transactions and blocks was used in versions 2, 3, and 4. The function added to bitcoin core manages the soft forking. You can learn more about this BIP feature here: bips/blob/master/bip-0034.mediawiki. M erkle Trees You called to retrieve the block information and received a Merkle root hash key. A Merkle tree is a binary tree. The root node of the Merkle tree holds all the hashed pairs of the tree. To help visualize this process, look at the following simple ASCII example of a binary list of a hashed tree: Transactions list: H(A)->H(B)->H(C)->H(D) Hash(A|B|C|D) / Hash(A|B) Hash(C|D) / / Hash(A) Hash(B) Hash(C) Hash(D) The block headers included in this Merkle root are a representation of the descendants of all the transactions in that block. HASH(A|B|C|D) is the Merkle root. Each element A, B, C, and D would be a hash of all the transactions in that block. In our example we have only one transaction in each block. 65 Chapter 2 Blockchain Nodes Merkle Root: H(A) / Hash(A) Target nBits The block header includes nBits. nBits is the target section of the block header. nBits is a 32-bit compact encoding of the 256-bit target threshold. It works like scientific notation but uses base-256 instead of base-10. Every 2,016-block bitcoin core re-target point and adjusts nBits according to bitcoin difficulty rules. Bitcoin difficulty increases or decreases depending on whether it took less time or more time than two weeks to find 2,016 blocks. In other words, the difficulty will increase if the hash rate increases or decrease if the network hash rate decreases. For instance, to convert an nBits 0x181b8330 into the target threshold, you would calculate it using the same shorthand you use with regular scientific notation; see Figure 2-21. Figure 2-21.  Calculating nBits. Photo credit. Convert 0x1bc3300000000000000000000000000000000000000000000 to nBits of 0x181b8330. That will be our target threshold. 66 Chapter 2 Blockchain Nodes txn_count The txn_count parameter represents the total number of transactions in a given block including the coinbase transaction. Coinbase is a special field used as an input for coinbase transactions. The coinbase allows you to claim the block reward and provides up to 100 bytes for arbitrary data. Each block contains transactions, and the first transaction in a block is created by a miner; it includes a single coinbase. Block Reward Bitcoin miners claim the reward for creating a block. The reward is the sum of block subsidies plus the transaction fees paid by transactions included in the block. A block subsidy is the newly available satoshis reward. It started at 50 bitcoins and is being halved every 210,000 blocks, approximately once every four years. At the time of writing, it’s about 12.5 bitcoins. Eighty percent of the block subsidy has already been paid, and only 4.2 million bitcoins are left to mine until the 21 million supply cap is reached. At that point, the miners will receive a reward of only transaction fees. As mentioned, each block contains transactions, and the first transaction in a block is created by a miner; it includes a single coinbase, the reward. txns: Decode a Transaction txns is the raw transaction in the block. To better understand this process, let’s work with an actual transaction. Bitcoin transactions that are stored in the blockchain ledger are broadcast between different peers in serialized byte format (raw format or raw transaction). To decode the SHA256 raw transaction, you can call the bitcoin client and utilize the different APIs. 67 Chapter 2 Blockchain Nodes To start, you can retrieve a block you would like to work with. The daemon you are running lists the blocks as the new best, as shown in Figure 2-22. Figure 2-22.  Bitcoin daemon printing to console result As you can see, you are able to find the new best block by looking at the output of the bitcoin daemon. In this case, you choose the hash 000000000000ea2ca199cafd1362ece59d7c6f3867b5e0d6f20c12af6752fb48. The best block chain is the block selected that is the hardest chain to re-create. Remember, in a chain of blocks, each block refers to the block that came before it; that’s how you have a blockchain that creates the security and prevents the double spending. Now that you have the new best block, you can retrieve the hash data of that block. > bitcoin-cli getblock 000000000000ea2ca199cafd1362ece59d7 c6f3867b5e0d6f20c12af6752fb48 The getblock command returns to a coded SHA256 hash data about the block you requested (Figure 2-23). 68 Chapter 2 Blockchain Nodes Figure 2-23.  getblock retrieving block information Let’s examine the result of the getblock call. You got a Merkle root as a hash as well as hash tx of all the transactions in that block. “tx”: [ “a73226fc261f95db14eba45cd734aeb0b8784911aeb24f301f94858 a09184036”, Transaction hash 02, Transaction hash 03, and so on… ] As you can see, there are multiple tx (transactions) in the array of this block. You can now request to retrieve the raw transaction data of each transaction (tx). 69 Chapter 2 Blockchain Nodes The getrawtransaction command will return the raw data. > bitcoin-cli getrawtransaction a73226fc261f95db14eba45cd734 aeb0b8784911aeb24f301f94858a09184036 Here is the raw transaction SHA256 data: 01000000010000000000000000000000000000000000000000000000000000 000000000000ffffffff070439f3001b0141ffffffff0100f2052a01000000 434104b5a750a0ca4bb5a47b6f169b8a8f42b39e2dbb7967d046f1bf018d 927d102c280f1123ebfd973f6e651f2e5ff4486e18a90cc67d6d17ccdb95cd6 bf028d791cfac00000000 You can now decode the SHA256 raw transaction data with the decoderawtransaction command. > bitcoin-cli decoderawtransaction 0100000001000000000000000000 0000000000000000000000000000000000000000000000ffffffff070439 f3001b0141ffffffff0100f2052a01000000434104b5a750a0ca4bb5a47 b6f169b8a8f42b39e2dbb7967d046f1bf018d927d102c280f1123ebfd973 f6e651f2e5ff4486e18a90cc67d6d17ccdb95cd6bf028d791cfac00000000 The command returns the transaction result in a readable format, as shown in Figure 2-24. Figure 2-24.  Decode transaction utilizing the decoderawtransaction command 70 Chapter 2 Blockchain Nodes B itcoin Wallet As you saw in Figure 2-24, the wallet address is 1Mr2G632PfQuq4uJXRBN WLoRKH71Qwor51, and the value is 50 coins. You can also confirm the transactions of this wallet online by visiting services that contain a full node and checking the wallet’s balance. Figure 2-25 shows a screenshot from 4uJXRBNWLoRKH71Qwor51. Figure 2-25.  1Mr2G632PfQuq4uJXRBNWLoRKH71Qwor51 wallet balance Similarly, you can query your wallet’s available funds via the CLI: > bitcoin-cli getbalance 1Mr2G632PfQuq4uJXRBNWLoRKH71Qwor51 71 Chapter 2 Blockchain Nodes In the next chapters, I will be covering wallets, so I will explain in more detail the wallet’s operations, but for now, you can see that the user purchased 50 coins in 2003 and sold them in 2012. Notice that although you do not know the identity of the person who owns the wallet, you are able to view the wallet’s current balance as this is public information. Summary In this chapter, you learned how to run a blockchain node that can help manage a blockchain. For bitcoin, you created a node called a miner. For NEO, you created a node that has management rights called a bookkeeping node, and for EOS you created a block producer. You also explored what you need to do to have your node elected or running so it is profitable. Next, you installed a full bitcoin node that is capable of running the bitcoin core API. You installed and configured your node and learned how to run the bitcoin core demon. You then interacted with the bitcoin core API and were able to learn how to serialize blocks and understand better the data inside each block. I covered block rewards, transactions, and the bitcoin wallet. In the next chapter, you will be building your very own blockchain P2P network to get a much deeper understanding of how a blockchain works. 72 Creating Your Own Blockchain In this chapter, I will cover how to build your very own blockchain P2P network. This is a seven-step process, so in each section I’ll start with a brief introduction followed by an exercise. You can download the code for each of the following exercises from GitHub and follow along: • Creating a basic P2P network • Sending and receiving blocks • Registering miners and creating new blocks • Setting up a name-value database, LevelDB • Creating a private-public wallet • Using API services • Creating a command-line interface This chapter will drill down into the code, and the examples in this chapter are simple in nature and intended for learning purposes. They will give you a better understanding of blockchain and the elements that are needed to achieve a fully working prototype of a blockchain. Chapter 3 Creating Your Own Blockchain Note  It’s not feasible to create a full production-grade blockchain in this short instructional chapter; however, I will give you the fundamentals for creating a basic working one. Creating a Basic P2P Network The first step in creating your blockchain is to create a P2P network. As you saw in previous chapters, the P2P network was the key to making blockchain work. In cryptocurrency the P2P network can help prevents the double spending issue for PoW and is also the core architecture behind PoS. In a blockchain, it allows you to sync any data needed on a network. Note  Peer-to-peer (P2P) is a type of computer network that uses a distributed architecture. Each peer or node shares the workload and is equal to the other peers, meaning there should not be any privileged peer. “We have proposed a system for electronic transactions without relying on trust. We started with the usual framework of coins made from digital signatures, which provides strong control of ownership, but is incomplete without a way to prevent double-spending. To solve this, we proposed a peer-topeer network using proof-of-work to record a public history of transactions that quickly becomes computationally impractical for an attacker to change if honest nodes control a majority of CPU proof-of-worker.” —Bitcoin: A Peer-to-Peer Electronic Cash System 74 Chapter 3 Creating Your Own Blockchain In this chapter, I will show you how to create your blockchain with Node.js, but you can do this with any other programming language because the principles are the same. You will be setting up your machine with the WebStorm integrated development environment (IDE) that will be used throughout this book. To download WebStorm, go to https:// WebStorm offers a 30-day trial; however, it’s not necessary, and you can choose any IDE of your liking and achieve the same results. At the time of writing, the WebStorm version is 2018.2. STEP 1: BASIC P2P NETWORK EXERCISE Setting Up Your Project In this exercise, you will set up your project and create a basic P2P network to send and receive messages. After you are able to send and receive messages, you will be able to create a block class and a chained library and tie several blocks together to create a blockchain. You will need Node.js installed on your machine; there are many ways to install it. One easy way is through the prebuilt installer manager; find one that fits your platform here: https:// After you have downloaded WebStorm, you can create a new project. Select File ➤ Create New Project ➤ Node.js Express App ➤ CREATE. In Location, call the project Blockchain, and click Create (see Figure 3-1). 75 Chapter 3 Creating Your Own Blockchain Figure 3-1.  WebStorm, creating a new project wizard Creating a P2P Network Create a folder and name it Blockchain. Then create a file and name it p2p.js and write the following code. Alternatively, you could just clone the code from GitHub. chapter2/step1/p2p.js > git clone Tip  You can clone the entire code listings in this book from GitHub. Use the following Terminal command: > git clone chapter3/step1/ 76 Chapter 3 Creating Your Own Blockchain Listing 3-1.  Shows Node.js P2P Network initial code to send and receive messages const crypto = require(‘crypto’), Swarm = require(‘discovery-swarm’), defaults = require(‘dat-swarm-defaults’), getPort = require(‘get-port’); const peers = {}; let connSeq = 0; let channel = ‘myBlockchain’; const myPeerId = crypto.randomBytes(32); console.log(‘myPeerId: ‘ + myPeerId.toString(‘hex’)); const config = defaults({ id: myPeerId, }); const swarm = Swarm(config); (async () => { const port = await getPort(); swarm.listen(port); console.log(‘Listening port: ‘ + port); swarm.join(channel); swarm.on(‘connection’, (conn, info) => { const seq = connSeq; const peerId =‘hex’); console.log(`Connected #${seq} to peer: ${peerId}`); if (info.initiator) { try { conn.setKeepAlive(true, 600); 77 Chapter 3 Creating Your Own Blockchain } catch (exception) { console.log(‘exception’, exception); } } conn.on(‘data’, data => { let message = JSON.parse(data); console.log(‘- Received Message start -‘); console.log( ‘from: ‘ + peerId.toString(‘hex’), ‘to: ‘ + peerId.toString(, ‘my: ‘ + myPeerId.toString(‘hex’), ‘type: ‘ + JSON.stringify(message.type) ); console.log(‘- Received Message end -‘); }); conn.on(‘close’, () => { console.log(`Connection ${seq} closed, peerId: ${peerId}`); if (peers[peerId].seq === seq) { delete peers[peerId] } }); if (!peers[peerId]) { peers[peerId] = {} } peers[peerId].conn = conn; peers[peerId].seq = seq; connSeq++ }) })(); 78 Chapter 3 Creating Your Own Blockchain setTimeout(function(){ writeMessageToPeers(‘hello’, null); }, 10000); writeMessageToPeers = (type, data) => { for (let id in peers) { console.log(‘- writeMessageToPeers start – ‘); console.log(‘type: ‘ + type + ‘, to: ‘ + id); console.log(‘- writeMessageToPeers end – ‘); sendMessage(id, type, data); } }; writeMessageToPeerToId = (toId, type, data) => { for (let id in peers) { if (id === toId) { console.log(‘- writeMessageToPeerToId start – ‘); console.log(‘type: ‘ + type + ‘, to: ‘ + toId); console.log(‘- writeMessageToPeerToId end – ‘); sendMessage(id, type, data); } } }; sendMessage = (id, type, data) => { peers[id].conn.write(JSON.stringify( { to: id, from: myPeerId, type: type, 79 Chapter 3 Creating Your Own Blockchain data: data } )); }; To get this example to work, you need to run two instances of this code. You can run it from two separate machines as would be done in real life, or you could run two instances from the same machine via Terminal. Your code needs to find and connect peers, deploy servers that are used to discover other peers, and get an available TCP port. That is done by utilizing these three libraries: – discovery-swarm: Used to create a network swarm that uses discovery-channel to find and connect peers – dat-swarm-defaults: Deploys servers that are used to discover other peers – get-port: Gets available TCP ports To install these libraries, run this command: > npm install crypto discovery-swarm dat-swarm-defaults get-port -save Now that are libraries are installed, open two Terminal instances and navigate to the location of the library. Run the following command: > node p2p.js To run the code from the clone library on GitHub, navigate to the code, follow these Terminal commands to install the libraries, and run a node.js instance attaching our p2p.js code: > cd [location]/chapter2/step2 > npm install > node p2p.js Figure 3-2 shows the output of running the Node.js code. 80 Chapter 3 Creating Your Own Blockchain Figure 3-2.  P2P running two peers in Terminal As you can see in Figure 3-2, the network generated a random peer ID for your machine and picked a random port utilizing the discovery libraries you installed. Then the code was able to discover other peers on the network and send and receive messages to and from these peers. You are now connected on a P2P network with other users. Let’s walk through the code to better understand how it all works. The first lines of code are an import statement for the open source libraries that you are using in your code. const crypto = require(‘crypto’), Swarm = require(‘discovery-swarm’), defaults = require(‘dat-swarm-defaults’), getPort = require(‘get-port’); Notice that you use const to set your variable instead of let. You want to ensure there is no rebinding, and you always refer to the same object, so selecting const is advised according to best practices. Next, you set your variables to hold an object with the peers and connection sequence, and you choose a channel name that all your nodes will be connecting to. You also set a randomly generated peer ID for your peer utilizing the crypto library. const peers = {}; let connSeq = 0; let channel = ‘myBlockchain’; 81 Chapter 3 Creating Your Own Blockchain const myPeerId = crypto.randomBytes(32); console.log(‘myPeerId: ‘ + myPeerId.toString(‘hex’)); Next, you generate a config object that holds your peer ID. Then you use the config object to initialize the swarm library. The swarm library can be found here: What it does is create a network swarm that uses the discovery-channel library to find and connect peers on a UCP/TCP network. const config = defaults({ id: myPeerId, }); const swarm = Swarm(config); Now that everything is set up and ready, you will be creating a Node.js async function to continuously monitor swarm.on event messages. (async () => { You listen on the random port selected, and once a connection is made to the peer, you use setKeepAlive to ensure the network connection stays with other peers. const port = await getPort(); swarm.listen(port); console.log(‘Listening port: ‘ + port); swarm.join(channel); swarm.on(‘connection’, (conn, info) => { const seq = connSeq; const peerId =‘hex’); console.log(`Connected #${seq} to peer: ${peerId}`); if (info.initiator) { try { conn.setKeepAlive(true, 600); 82 Chapter 3 Creating Your Own Blockchain } catch (exception) { console.log(‘exception’, exception); } } Once you receive a data message on the P2P network, you parse the data using JSON.parse, which is a Node.js native command, so you do not need to include any import statement. This command decodes your message back into an object, and the toString command converts bytes into a readable string data type. conn.on(‘data’, data => { let message = JSON.parse(data); console.log(‘- Received Message start -‘); console.log( ‘from: ‘ + peerId.toString(‘hex’), ‘to: ‘ + peerId.toString(, ‘my: ‘ + myPeerId.toString(‘hex’), ‘type: ‘ + JSON.stringify(message.type) ); console.log(‘- Received Message end -‘); }); You also listen to a close event, which will indicate that you lost a connection with peers, so you can take action, such as delete the peers from your peers list object. conn.on(‘close’, () => { console.log(`Connection ${seq} closed, peerId: ${peerId}`); if (peers[peerId].seq === seq) { delete peers[peerId] } }); 83 Chapter 3 Creating Your Own Blockchain if (!peers[peerId]) { peers[peerId] = {} } peers[peerId].conn = conn; peers[peerId].seq = seq; connSeq++ }) })(); Here, you will be using a setTimeout Node.js native function to send a message after ten seconds to any available peers. The first message you will be sending is just an “hello” message. You create methods called writeMessageToPeers and writeMessageToPeerToId to handle your object, so it’s formatted with the data you want to transmit and who you want to send it to. setTimeout(function(){ writeMessageToPeers(‘hello’, null); }, 10000); The writeMessageToPeers method will be sending messages to all the connected peers. writeMessageToPeers = (type, data) => { for (let id in peers) { console.log(‘- writeMessageToPeers start – ‘); console.log(‘type: ‘ + type + ‘, to: ‘ + id); console.log(‘- writeMessageToPeers end – ‘); sendMessage(id, type, data); } }; 84 Chapter 3 Creating Your Own Blockchain Additionally, you will be creating another method, writeMessageToPeerToId, that will be sending the message to a specific peer ID, in case you want to communicate with just one specific peer. writeMessageToPeerToId = (toId, type, data) => { for (let id in peers) { if (id === toId) { console.log(‘- writeMessageToPeerToId start – ‘); console.log(‘type: ‘ + type + ‘, to: ‘ + toId); console.log(‘- writeMessageToPeerToId end – ‘); sendMessage(id, type, data); } } }; Lastly, sendMessage is a generic method that you will be using to send a message formatted with the params you would like to pass and includes the following: – to/from: The peer ID you are sending the message from and to – type: The message type – data: Any data you would like to share on the P2P network These params will be useful once you share your blockchain block. Notice that the message you pass needs to be a string and cannot be an object, so you are using a JSON.stringify native function to encode your messages before sharing them over the P2P network. sendMessage = (id, type, data) => { peers[id].conn.write(JSON.stringify( { to: id, from: myPeerId, 85 Chapter 3 Creating Your Own Blockchain type: type, data: data } )); }; In this exercise, you downloaded and installed the WebStorm IDE and created your project, which includes a basic P2P network. You were able to keep a connection to a TCP network random port and send and receive messages including encoding and decoding these messages. You are ready to move to the next exercise and send an actual block between each node on your network. Creating Genesis Block and Sharing Blocks In the next exercise, you will be creating block objects that you can share between your nodes. But before you do that, let’s take a closer look at the Block object. The Block object is not the same for every blockchain. Different blockchains utilize different types of Block objects; you will be using a Block object similar to bitcoin; I covered in details during Chapter 2. To better understand the architecture, take a look at a Unified Modeling Language (UML) diagram of the Block and the BlockHeader objects you will be using in the next exercise, as shown in Figure 3-3. 86 Chapter 3 Creating Your Own Blockchain Figure 3-3.  Block and BlockHeader UML diagram As a reminder, from Chapter 2, the Block object contains the following properties: • index: GenesisBlock is our first block, we assign the block index with the value of 0. • txns: This is the raw transaction in the block. I don’t want to focus on just cryptocurrencies in this chapter, so think of this as any type of data you want to store. 87 Chapter 3 Creating Your Own Blockchain Included in the Block object is the BlockHeader object, which contains the following properties: • Version: At the time of writing, there are four block versions. Version 1 is the genesis block (2009), and version 2 is a soft fork of bitcoin core 0.7.0 (2012). Version 3 blocks were a soft fork of bitcoin core 0.10.0 (2015). Version 4 blocks are BIP65 in bitcoin core 0.11.2 (2015). • Previous block header hash: This is an SHA-256 (Secure Hash Algorithm) hash function of the previous block’s header. It ensures that the previous block cannot be changed as this block needs to be changed as well. • Merkle root hash: A Merkle tree is a binary tree that holds all the hashed pairs of the tree. • Time: This is the Unix epoch time when the miner started hashing the header. As you recall, bitcoin also includes a difficulty property for the miners that gets recalculated every 2,016 blocks. Here you won’t use the nBits and nounce params, as you are not doing PoW. • nounce: The nonce in a bitcoin block is a 32-bit (4-byte) field whose value is adjusted by miners so that the hash of the block will be less than or equal to the current target of the network. • nBits: This refers to the target. The target is a 256-bit number and inversely proportional to the difficulty. It is recalculated every 2,016 blocks. In terms of P2P communication, the flow of blocks between each peer on the P2P network consists of requesting the latest block from a peer on the network and then receiving a block request. Figure 3-4 shows the flow diagram. 88 Chapter 3 Creating Your Own Blockchain Figure 3-4.  Flow diagram of P2P communications requesting latest block and receiving latest block 89 Chapter 3 Creating Your Own Blockchain Now that you understand the architecture and the flow of blocks in the P2P network, in the following exercise you will be sending and requesting blocks. STEP 2: P2P NETWORK SENDING BLOCKS EXERCISE Setting Up a Block Class and Chain Library In this exercise, you will create your blockchain. The blockchain consists of two files: block.js and chain.js. The file Block.js will hold the block class object, and chain.js will be the glue with methods to handle the interactions with the blocks. In terms of the Block object, you will be creating properties similar to the properties that bitcoin core holds. Take a look at Listing 3-2, block.js file include Block and BlockHeader objects. Listing 3-2.  block.js exports.BlockHeader = class BlockHeader { constructor(version, previousBlockHeader, merkleRoot, time) { this.version = version; this.previousBlockHeader = previousBlockHeader; this.merkleRoot = merkleRoot; this.time = time; } }; exports.Block = class Block { constructor(blockHeader, index, txns) { this.blockHeader = blockHeader; this.index = index; this.txns = txns; } } 90 Chapter 3 Creating Your Own Blockchain As you can see, chain.js contains the first block, which is called the genesis block, as well as a method to receive the entire blockchain object, add a block, and retrieve a block. Note that you will be adding a library called moment to save the time in a Unix time format in your chain.js library. To do so, install moment with npm. > npm install moment -save Now that you have the block.js file created, you can create the chain.js class; see Listing 3-3. Listing 3-3.  chain.js let Block = require(“./block.js”).Block, BlockHeader = require(“./block.js”).BlockHeader, moment = require(“moment”); let getGenesisBlock = () => { let blockHeader = new BlockHeader(1, null, “0x1bc33000000000 00000000000000000000000000000000000”, moment().unix()); return new Block(blockHeader, 0, null); }; let getLatestBlock = () => blockchain[blockchain.length-1]; let addBlock = (newBlock) => { let prevBlock = getLatestBlock(); if (prevBlock.index < newBlock.index && newBlock. blockHeader.previousBlockHeader === prevBlock.blockHeader. merkleRoot) { blockchain.push(newBlock); } } let getBlock = (index) => { if (blockchain.length-1 >= index) 91 Chapter 3 Creating Your Own Blockchain return blockchain[index]; else return null; } const blockchain = [getGenesisBlock()]; if (typeof exports != ‘undefined’ ) { exports.addBlock = addBlock; exports.getBlock = getBlock; exports.blockchain = blockchain; exports.getLatestBlock = getLatestBlock; } You now have a block object that is included in chain.js. Your library can create your genesis block and add a block to your blockchain object. You also will be able to send and request blocks. Next, in your P2P network class, you can use the chain.js file you created. First you need to import the class chain.js. const chain = require(“./chain”); Then you can define a message type to request and receive the latest block. When you send messages in your P2P network, you need to be able to figure out the purpose of messages. By using a MessageType property, you can define a switch mechanism so different messages types will be used for different functions. let MessageType = { REQUEST_LATEST_BLOCK: ‘requestLatestBlock’, LATEST_BLOCK: ‘latestBlock’ }; Once a connection data event message is received, you can create your switch code to handle the different types of requests, as shown in Listing 3-4. 92 Chapter 3 Creating Your Own Blockchain Listing 3-4.  Message Switch and Handlers switch (message.type) { case MessageType.REQUEST_BLOCK: console.log(‘-REQUEST_BLOCK-‘); let requestedIndex = (JSON.parse(JSON.stringify(message. data))).index; let requestedBlock = chain.getBlock(requestedIndex); if (requestedBlock) writeMessageToPeerToId(peerId.toString(‘hex’), MessageType.RECEIVE_NEXT_BLOCK, requestedBlock); else console.log(‘No block found @ index: ‘ + requestedIndex); console.log(‘-REQUEST_BLOCK-‘); break; case MessageType.RECEIVE_NEXT_BLOCK: console.log(‘-RECEIVE_NEXT_BLOCK-‘); chain.addBlock(JSON.parse(JSON.stringify(; console.log(JSON.stringify(chain.blockchain)); let nextBlockIndex = chain.getLatestBlock().index+1; console.log(‘- request next block @ index: ‘ + nextBlockIndex); writeMessageToPeers(MessageType.REQUEST_BLOCK, {index: nextBlockIndex}); console.log(‘-RECEIVE_NEXT_BLOCK-‘); break; } Lastly, you will set a timeout request that will send a request to retrieve the latest block every 5,000 milliseconds (5 seconds). setTimeout(function(){ writeMessageToPeers(MessageType.REQUEST_BLOCK, {index: chain. getLatestBlock().index+1}); }, 5000); 93 Chapter 3 Creating Your Own Blockchain You can download the complete exercise from here: Apress/the-blockchain-developer/tree/master/chapter3/step2/. In this exercise, you were able to generate your genesis block and create a mechanism to request and receive blocks by sending messages requests. The ability to request and receive blocks allows you to sync new peers that enter the P2P network. You also need a sync for any additional blocks you generate after the genesis block creation. Registering Miners and Creating New Blocks At this point, you have a basic P2P network, and you are able to connect peers in the network, create a genesis block, and send and receive blocks. The next step is being able to generate new blocks. As you saw in Chapter 2, proof of work is based on creating a mathematical problem and rewarding miners that find the solution for the problem first. However, in this example, you will take an approach of proof of stake (PoS) where you trust each miner to generate your blocks. Each peer will register as a miner and will take a turn to mine a block. You can see an overview of each miner generating a block in Figure 3-5. 94 Chapter 3 Creating Your Own Blockchain Figure 3-5.  Your blockchain handles mining using a simple PoS mechanism Lastly, before you start your next exercise, revisit Figure 3-4 to better understand your flow. The flow shows how your P2P network handles peer communications requesting the latest block and receiving the latest block. In the next exercise, you will register your peers as miners and create new blocks. STEP 3: REGISTER MINERS AND CREATING NEW BLOCKS EXERCISE Register Miners In this exercise, you will register miners and create new blocks. You can download the complete exercise from here: the-blockchain-developer/tree/master/chapter3/step3. 95 Chapter 3 Creating Your Own Blockchain To automate the process of generating a block every x number of minutes, you can use a Node.js library called cron, which is similar to the Linux library that automates tasks. To install the cron open source library, run the following command: > npm install cron -save Next, in your p2p.js file, you will create two variables to keep track of the registered miners as well as who mined the last block so you can assign the next block to the next miner. let registeredMiners = []; let lastBlockMinedBy = null; You are also going to add two messages types. • REQUEST_ALL_REGISTER_MINERS • REGISTER_MINER let MessageType = { REQUEST_BLOCK: ‘requestBlock’, RECEIVE_NEXT_BLOCK: ‘receiveNextBlock’, RECEIVE_NEW_BLOCK: ‘receiveNewBlock’, REQUEST_ALL_REGISTER_MINERS: ‘requestAllRegisterMiners’, REGISTER_MINER: ‘registerMiner’ }; Before you register your peers as miners, you will request to receive all the existing registered miners in the network, and then you will add your peer as a miner in a registeredMiners object. You do that by running a timer to update your miners every five seconds. setTimeout(function(){ writeMessageToPeers(MessageType.REQUEST_ALL_REGISTER_MINERS, null); }, 5000); 96 Chapter 3 Creating Your Own Blockchain Now, that have an automated timeout command that can point to a handler to update the list of registered miners you can also automate a command to register your peer as a miner; setTimeout(function(){ registeredMiners.push(myPeerId.toString(‘hex’)); console.log(‘-Register my miner -‘); console.log(registeredMiners); writeMessageToPeers(MessageType.REGISTER_MINER, registeredMiners); console.log(‘- Register my miner -‘); }, 7000); In your switch command, you want to modify the code to be able to set handlers for incoming messages regarding the registrations of miners. You want to keep track of the registered miners as well as handle a message once a new block is mined. See Listing 3-5 for the miner’s handlers. Listing 3-5.  Miner’s Handlers case MessageType.REQUEST_ALL_REGISTER_MINERS: console.log(‘-REQUEST_ALL_REGISTER_ MINERS- ‘ +; writeMessageToPeers(MessageType.REGISTER_MINER, registeredMiners); registeredMiners = JSON.parse(JSON.stringify(message. data)); console.log(‘-REQUEST_ALL_REGISTER_ MINERS- ‘ +; break; case MessageType.REGISTER_MINER: console.log(‘-REGISTER_MINER- ‘ +; let miners = JSON.stringify(; registeredMiners = JSON.parse(miners); 97 Chapter 3 Creating Your Own Blockchain console.log(registeredMiners); console.log(‘-REGISTER_MINER- ‘ +; break; Unregister Miners You also need to unregister a miner once a connection with the miner is closed or lost. console.log(`Connection ${seq} closed, peerId: ${peerId}`); if (peers[peerId].seq === seq) { delete peers[peerId]; console.log(‘- registeredMiners before: ‘ + JSON. stringify(registeredMiners)); let index = registeredMiners.indexOf(peerId); if (index > -1) registeredMiners.splice(index, 1); console.log(‘- registeredMiners end: ‘ + JSON. stringify(registeredMiners)); } }); Mine a New Block As opposed to bitcoin, which generates a block every 10 minutes, your blockchain will be improved and will generate a block every 30 seconds. To achieve that, you already installed the open source cron library for Node.js. The cron library works the same as the Linux cron. You can utilized the cron library to set how often to call the same code again, which will be used to call your miners every 30 seconds. To do so, first include the library in your code’s import statement on top of the p2p.js file. let CronJob = require(‘cron’).CronJob; 98 Chapter 3 Creating Your Own Blockchain Next, you can set your cronjob to run every 30 seconds, and job.start(); will start the job, as shown in Listing 3-6. Listing 3-6.  crobjob to Mine a New Block const job = new CronJob(’30 ∗ ∗ ∗ ∗ ∗’, function() { let index = 0; // first block if (lastBlockMinedBy) { let newIndex = registeredMiners.indexOf(lastBlockMinedBy); index = ( newIndex+1 > registeredMiners.length-1) ? 0 : newIndex + 1; } lastBlockMinedBy = registeredMiners[index]; console.log(‘- REQUESTING NEW BLOCK FROM: ‘ + registeredMiners[index] + ‘, index: ‘ + index); console.log(JSON.stringify(registeredMiners)); if (registeredMiners[index] === myPeerId.toString(‘hex’)) { console.log(‘-create next block -‘); let newBlock = chain.generateNextBlock(null); chain.addBlock(newBlock); console.log(JSON.stringify(newBlock)); writeMessageToPeers(MessageType.RECEIVE_NEW_BLOCK, newBlock); console.log(JSON.stringify(chain.blockchain)); console.log(‘-create next block -‘); } }); job.start(); 99 Chapter 3 Creating Your Own Blockchain Reviewing the code, notice that the first block’s index is 0, so after the first block is mined, lastBlockMinedBy will be set, and you will be requesting the next block from your next miner. let newIndex = registeredMiners.indexOf(lastBlockMinedBy); index = ( newIndex+1 > registeredMiners.length-1) ? 0 : newIndex + 1; To generate and add a new block, you will be calling chain generateNextBlock and addBlock. Lastly, you will broadcast the new block to all the connected peers. let newBlock = chain.generateNextBlock(null); chain.addBlock(newBlock); writeMessageToPeers(MessageType.RECEIVE_NEW_BLOCK, newBlock); In your code, your switch will handle the new incoming blocks. case MessageType.RECEIVE_NEW_BLOCK: if ( === myPeerId.toString(‘hex’) && message.from !== myPeerId.toString(‘hex’)) { console.log(‘-RECEIVE_NEW_BLOCK- ‘ +; chain.addBlock(JSON.parse(JSON.stringify(; console.log(JSON.stringify(chain.blockchain)); console.log(‘-RECEIVE_NEW_BLOCK- ‘ +; } break; To see this code in action, run three instances of your code. > node p2p.js You can see the messages of registering each peer as a miner, as well as your code starting to mine blocks every 30 seconds in order, as shown in Figure 3-6. 100 Chapter 3 Creating Your Own Blockchain Figure 3-6.  Code registering miners and generating new blocks In this exercise, you were able to register your peers as a miners, generate new blocks, and share blocks with other peers; you used a simple PoS for the consensus mechanism and were able to test the functionality by creating three peers. The consensus mechanism is simple and does not take into account every use case that can happen or security. In the next step, you will save your blocks in a LevelDB database. Storing Blocks in LevelDB If you run your blockchain for a few hours, you will notice that the number of blocks created grows, which can become a problem as currently these blocks are stored in your computer’s memory cache. As you add more and more blocks, the memory usage will grow, and eventually your code will crash. Further, without storing your blocks in a database, you will not be able to start and stop your P2P network, as the blocks are not saved. To accommodate these use cases and others, you will be using a LevelDB database. 101 Chapter 3 Creating Your Own Blockchain Note A LevelDB database stores name-value pairs in what is called a level-up and level-down fashion. It is an ideal option for blockchain networks. In fact, bitcoin uses LevelDB to store not only block information but also transaction information. See ­https://github. com/bitcoin-core/leveldb. STEP 4: LEVELDB TO STORE BLOCKS EXERCISE LevelDB In this exercise, you will implement a database to store your blocks. You can download the complete exercise from here: Apress/the-blockchain-developer/tree/master/chapter3/ step4/blockchain. Remember to run the install command to retrieve all the npm modules. > npm install To get started on your own from the previous step, you will be using a Node. js LevelDB wrapper so you can communicate with LevelDB through your code. Install the library via npm. > npm install level -save Next, make a directory where you will be saving the database. > mkdir db You can now implement the database. In your chain.js library, you will add some code to save your block in the LevelDB database, as shown in Listing 3-7. 102 Chapter 3 Creating Your Own Blockchain Listing 3-7.  Storing Blocks in LevelDB let level = require(‘level’), fs = require(‘fs’); let db; let createDb = (peerId) => { let dir = __dirname + ‘/db/’ + peerId; if (!fs.existsSync(dir)){ fs.mkdirSync(dir); db = level(dir); storeBlock(getGenesisBlock()); } } As you can see, you use the __dirname Node.js native class to give you the directory path location because you need the full path to save your database. Because you are running multiple instances of your P2P network on the same machine, you cannot use the same path for each peer because the database needs to be separate. What you can do is set each database’s location in a separate path location using the folder name as the name of your peer ID; then each database can be stored in the db folder. Also notice that you save the first block, getGenesisBlock(). Next, you create a storeBlock method to store the new block. let storeBlock = (newBlock) => { db.put(newBlock.index, JSON.stringify(newBlock), function (err) { if (err) return console.log(‘Ooops!’, err) // some kind of I/O error console.log(‘- Inserting block index: ‘ + newBlock. index); }) } 103 Chapter 3 Creating Your Own Blockchain When you generate a new block using the generateNextBlock method, you can now store the block in the LevelDB database. storeBlock(newBlock); You are also going to add a method to be able to retrieve a block from the LevelDB database. let getDbBlock = (index, res) => { db.get(index, function (err, value) { if (err) return res.send(JSON.stringify(err)); return(res.send(value)); }); } Make sure you expose the createDb and getDbBlock methods. if (typeof exports != ‘undefined’ ) { exports.createDb = createDb; exports.getDbBlock = getDbBlock;} Lastly, in your P2P network code, all you need to do is create a database once you start the code. chain.createDb(myPeerId.toString(‘hex’)); To see the code in action, run an instance of the P2P network. > node p2p.js You can monitor the database’s data in the db folder using the tail command with the -f flag. Terminal will stay open and can show you new blocks as they are being generated (see the output in Figure 3-7). > cd step4/db/[our peer Id] > tail -f 000003.log 104 Chapter 3 Creating Your Own Blockchain Figure 3-7.  tail command with the LevelDB database showing new blocks being generated In this exercise, you created a LevelDB database. You are storing your blocks so you will be able to retrieve them instead of relying on your cache memory. I am keeping things simple; if this were a real working blockchain, you would implement the following steps: 1. Mitigate all the possible security risks. 2. Store and retrieve your blocks from the LevelDB database. 3. Create a method to restore LevelDB’s entries. 4. Clean old databases because new ones are created on every init. Creating a Blockchain Wallet In cryptocurrency, a wallet is necessary in order to reward miners for generating blocks as well as to be able to create transactions and send transactions. In this section, you will create a wallet. You need to create a combination of public and private keys not just to authenticate a user but so you can store and retrieve data that the user owns. You will create a wallet with public and private keys. In bitcoin, the wallet’s original software is the bitcoin core protocol you downloaded in Chapter 2; it needs the entire ledger of all transactions since 2009, which is more than 150 GB at the time of writing. For that 105 Chapter 3 Creating Your Own Blockchain reason, most wallets in use are “light” wallets or what’s called simplified payment verification (SPV) wallets that sync to bitcoin core. In blockchain, there are many different wallets available, from online all the way to a paper wallet where you write your private key on a piece of paper. Before proceeding, let’s take a quick look at how you can communicate with a bitcoin wallet. As you recall, in Chapter 2 you were able to get the balance of a certain bitcoin wallet. To better understand wallets, you can create a bitcoin wallet using the bitcoin core. First, you need to run the bitcoin daemon. > bitcoind -printtoconsole Next, you can request an address. > bitcoin-cli help getnewaddress Then, you are able to dump your private keys into a text file. > bitcoin-cli dumpwallet ~/mywallet.txt You can get the location of your private key and view the key. > vim /Users/[location]/mywallet.txt For reference, check the C++ bitcoin core wallet code here: > vim /[Bitcoin Core Location]/bitcoin/src/wallet/init.cpp STEP 5: WALLET EXERCISE Create a Blockchain Wallet In this exercise, you will generate public-private keys to be used for your wallet. You can download the complete exercise from ­https://github. com/Apress/the-blockchain-developer/tree/master/chapter3/ step5/blockchain and run the npm install command. Additionally, create a folder named wallet. 106 Chapter 3 Creating Your Own Blockchain > npm install > mkdir wallet You will be using the elliptic-curve cryptography library implementation to generate private-public key combos. Note that the elliptic-curve library uses secp256k1 as the ECDSA curve algorithm. Note  Elliptical curve cryptography (ECC) is the public key encryption technique used by bitcoin. It’s based on elliptic curve theory to generate the cryptographic keys. Secp256k1 is the graph elliptic curve ECDSA algorithm. To install the library, run the following command: > npm install elliptic -save Next, add a file and name it wallet.js. Take a look at the complete code in Listing 3-8. Listing 3-8.  wallet.js let EC = require(‘elliptic’).ec, fs = require(‘fs’); const ec = new EC(‘secp256k1’), privateKeyLocation = __dirname + ‘/wallet/private_key’; exports.initWallet = () => { let privateKey; if (fs.existsSync(privateKeyLocation)) { const buffer = fs.readFileSync(privateKeyLocation, ‘utf8’); privateKey = buffer.toString(); } else { privateKey = generatePrivateKey(); fs.writeFileSync(privateKeyLocation, privateKey); } 107 Chapter 3 Creating Your Own Blockchain const key = ec.keyFromPrivate(privateKey, ‘hex’); const publicKey = key.getPublic().encode(‘hex’); return({‘privateKeyLocation’: privateKeyLocation, ‘publicKey’: publicKey}); }; const generatePrivateKey = () => { const keyPair = ec.genKeyPair(); const privateKey = keyPair.getPrivate(); return privateKey.toString(16); }; In the wallet file, you create and initialize the EC context. const ec = new EC(‘secp256k1’), You then store the location of your wallet’s private key, privateKeyLocation. privateKeyLocation = __dirname + ‘/wallet/private_key’; Next, you are able to create a method exports.initWallet to generate the actual public-private key, generatePrivateKey. const keyPair = ec.genKeyPair(); const privateKey = keyPair.getPrivate(); Notice that you will be generating a new wallet only if one doesn’t exist. if (fs.existsSync(privateKeyLocation)) In this exercise, you create a wallet.js file utilizing the Elliptic Curve Cryptography library to generate your private-public key combo. 108 Chapter 3 Creating Your Own Blockchain To see the code working, add the following code temporarily at the end of the wallet.js file. The script will create the public and private keys. let wallet = this; let retVal = wallet.initWallet(); console.log(JSON.stringify(retVal)); Next, create a wallet directory to store the private key and run the script. The code will initialize the script and create your public key. > mkdir wallet > node wallet.js > cat wallet/private_key When you run the node wallet.js command, you can see the public key. See Figure 3-8 for the output. Figure 3-8.  Generating a wallet’s private-public key Remember to comment out these lines because in the next exercise, you will create an API to be able to create your keys via the browser. C reating an API The next step is creating an application program interface (API) to be able to access the code you write. This is an important part of a blockchain, as you want to access your blocks and wallet or any other P2P network operation using an HTTP service. In this section, you will be using the express library, as it’s easy to run, and you will be able to create your API easily. 109 Chapter 3 Creating Your Own Blockchain STEP 6: API P2P BLOCKCHAIN EXERCISE Creating API In this exercise, you will create an API to interact with your P2P blockchain network. You can download the complete exercise from here: master/chapter3/step6/blockchain. You will be creating the following services: • blocks: Retrieves all the blocks in the blockchain • getBlock: Retrieves a specific block by index • getDBBlock: Retrieves a block from the database • getWallet: Creates a new wallet by generating a public-private key You will install express and body-parser. These libraries will allow you to create a server and display pages in the browser. > npm install express body-parser -save You also need to import the wallet.js file you created. let express = require(“express”), bodyParser = require(‘body-parser’), wallet = require(‘./wallet’); Next, you create a method called initHttpServer that will initiate the server and create the services. As you utilize different instances of the P2P network and run instances on the same computer, you want to utilize different port numbers. It’s common to use port 80 or 8081 for HTTP services but not required. What you will do is pass the random port number you are using and utilize the slice method to get the last two digits of the port number. 110 Chapter 3 Creating Your Own Blockchain let initHttpServer = (port) => { let http_port = ’80’ + port.toString().slice(-2); let app = express(); app.use(bodyParser.json()); The Blocks service will be retrieving all of your blocks. app.get(‘/blocks’, (req, res) => res.send(JSON.stringify( chain.blockchain ))); The getBlock service will be retrieving one block based on an index. app.get(‘/getBlock’, (req, res) => { let blockIndex = req.query.index; res.send(chain.blockchain[blockIndex]); }); The getDBBlock service will be retrieving a LevelDB database entry based on an index. app.get(‘/getDBBlock’, (req, res) => { let blockIndex = req.query.index; chain.getDbBlock(blockIndex, res); }); The getWallet service will be utilizing the wallet.js file you created in the previous step and generate your public-private key pair. app.get(‘/getWallet’, (req, res) => { res.send(wallet.initWallet()); }); Lastly, you will utilize the Express listen method. app.listen(http_port, () => console.log(‘Listening http on port: ‘ + http_port)); }; 111 Chapter 3 Creating Your Own Blockchain You will call the initHttpServer method you created after you start the P2P network and a random port was selected. (async () => { const port = await getPort(); initHttpServer(port); } To call your services, run the P2P network, and then you can open a browser and call the API. http://localhost:80[port]/getWallet http://localhost:80[port]/blocks http://localhost:80[port]/getBlock?index=0 http://localhost:80[port]/ getDBBlock?index=0 See Figure 3-9, for instance, as you retrieve all the blocks in your blockchain. Figure 3-9.  Retrieving all the blocks in your blockchain In this exercise, you created API services, and you can now interact with your P2P network. You created your services so you will be able to create multiple instances of the P2P networks on the same machine; however, in reality, every machine will be holding only one peer. In the next exercise, you will create a command-line interface (CLI) to easily call these services. 112 Chapter 3 Creating Your Own Blockchain Creating a Command-Line Interface For the last step in this chapter, you will be creating a command-line interface (CLI). The CLI is needed to be able to easily access the services you created. I won’t get into the entire internal process of the CLI script, as it’s beyond the scope of this chapter; however, you can download the whole example and review it. STEP 7: CLI EXERCISE Block Command In this exercise, you will create a CLI to interact with and access your P2P blockchain network. You can download the complete exercise from here: master/chapter3/step7/blockchain. Next, install the libraries you will be utilizing to run promises, run the async function, add colors to the console, and store cookies. > npm babel-polyfill async update-notifier handlebars colors nopt -save In the block.js command, you will be setting two commands: get and all. Take a look at the entire code in Listing 3-9. Listing 3-9.  Block Command Code let logger = require(‘../logger’); function Block(options) { this.options = options; } 113 Chapter 3 Creating Your Own Blockchain Block.DETAILS = { alias: ‘b’, description: ‘block’, commands: [‘get’, ‘all’], options: { create: Boolean }, shorthands: { s: [‘-get’], a: [‘-all’] }, payload: function(payload, options) { options.start = true; }, }; = function() { let instance = this, options = instance.options; if (options.get) { instance.runCmd(‘curl http://localhost:’ + options.argv. original[2] + ‘/getBlock?index=’ + options.argv.original[3]); } if (options.all) { instance.runCmd(‘curl http://localhost:’ + options.argv. original[2] + ‘/blocks’); } }; Block.prototype.runCmd = function(cmd) { const { exec } = require(‘child_process’); logger.log(cmd); exec(cmd, (err, stdout, stderr) => { 114 Chapter 3 Creating Your Own Blockchain if (err) { logger.log(`err: ${err}`); return; } logger.log(`stdout: ${stdout}`); }); }; exports.Impl = Block; As you can see, the wallet.js command will include the get and all methods to point to a curl command to run the HTTP service call. Wallet Command Similarly, the block.js command will include a create method and a curl command to run the HTTP service call. See Listing 3-10. Listing 3-10.  Wallet Command Code let logger = require(‘../logger’); function Wallet(options) { this.options = options; } Wallet.DETAILS = { alias: ‘w’, description: ‘wallet’, commands: [‘create’], options: { create: Boolean }, shorthands: { c: [‘-create’] }, 115 Chapter 3 Creating Your Own Blockchain payload: function(payload, options) { options.start = true; }, }; = function() { let instance = this, options = instance.options; if (options.create) { instance.runCmd(‘curl http://localhost:’ + options.argv. original[2] + ‘/getWallet’); } }; Wallet.prototype.runCmd = function(cmd) { const { exec } = require(‘child_process’); logger.log(cmd); exec(cmd, (err, stdout, stderr) => { if (err) { logger.log(`err: ${err}`); return; } logger.log(`stdout: ${stdout}`); }); }; exports.Impl = Wallet; Now that you have your commands set up, you can add your CLI to the bash_ profile as an alias to be able to run the CLI from any path location. > vim ~/.bash_profile alias cli=’node /[project location]/step7/bin/bin/cli.js 116 Chapter 3 Creating Your Own Blockchain Save and run bash_profile to apply these changes. > . ~/.bash_profile You can call the CLI once you run the P2P and know the ports you are using. > cli block -get [port] 1 #port #index > cli block -all [port] #port > cli wallet -create [port] For instance, run an instance of the P2P network in Terminal. > node p2p.js Next, open a new window terminal and run the CLI command to retrieve the first generated block. > cli block -get [port] 1 You can see the output in Figures 3-10 and 3-11. Figure 3-10.  Running the P2P blockchain network on port 8057 117 Chapter 3 Creating Your Own Blockchain Figure 3-11.  Retrieving blocks on port 8057 In this exercise, you created two commands for getting blocks and creating your wallet. This is a starting point for your CLI, and you will be able to continue to add commands as needed. Where to Go from Here I already mentioned that the code in this chapter does not take into account many use cases and has no security to keep it simple. There are many things you can do to improve the code. 118 • Confirmations: Each miner sends a message with a block. You can create a confirmation system to ensure the integrity of the data. • Transactions/data: You could implement transactions or data objects to address double spending, transaction validation, and coinbase transactions. • levelDB: Once the P2P is initialized, you can create a script to retrieve and write all the blocks into the LevelDB database, validate them, and clean the database as needed. Chapter 3 Creating Your Own Blockchain Summary This chapter covered how to create your very own basic P2P blockchain network; you were able to send and receive messages and include blocks in these messages. You were able to register and unregister miners and implement a simple PoS consensus mechanism. You created new blocks and sent them between the peers. You also set up a name-value LevelDB database to store blocks. You continued and created a wallet that consists of private-public key pairs. Lastly, you created ways to communicate with your P2P network via API services and the CLI. In the next chapter, you will be diving deep into understanding bitcoin wallets and transactions by interacting with the bitcoin core API. 119 Bitcoin Wallets and Transactions In this chapter, you will be diving deep into bitcoin’s core RPC and learn about wallets and transactions. You will learn how to utilize legacy and SegWit’s bitcoin wallets. You will extract a wallet’s public and private keys. The majority of this chapter will deal with transactions, from sending funds in a simple way utilizing bitcoin’s testing blockchain to more complex transactions. Additionally, you will learn how to send coins via bitcoin’s core wallet GUI, and you will learn how to view transactions in the Block Explorer and understand confirmations. You will look into raw transactions and learn how to create a raw transaction with one output as well as how to create transactions with multiple users signing them. Additionally, you will replace your transaction and set a lock time. You will also learn the difference between pay options and fees. Lastly, I will cover how to pass data in a raw transaction. By the end of this chapter, you will have a much better understanding of transactions, wallets, fees, payment options, and bitcoin’s core RPC. Bitcoin Core RPC Resources You learned how to interact with bitcoin core utilizing the bitcoin daemon and bitcoin core function as an HTTP JSON-RPC server, and you are now Chapter 4 Bitcoin Wallets and Transactions able to make calls and receive JSON responses. In this section, you will build on these skills to understand wallets and transactions. The first step is to initialize and run the bitcoin daemon. > bitcoind -printtoconsole Then in a different Terminal window, you can view the available RPC commands by running the help command. > bitcoin-cli help You can also request help on any command you run by adding help before the command. For instance, add help before the getnewaddress command like this: > bitcoin-cli help getnewaddress At the time of writing, the latest RPC version is bitcoin core version v0.18.99.0-56376f336 (release build); as new versions of bitcoin core are released, the commands in this chapter may change, so it’s useful to check for the latest RPC commands. Note that documentation for v0.18 is not live at the time of writing; v0.17 is the latest doc ( In the menu on the right, select RAWTRANSACTIONS and WALLET for a list of RPC commands relevant to this chapter. Note  In addition to bitcoin core documentation, there are two free web resources that can help you better understand the bitcoin RPC command line beyond what is covered in this chapter. They are­ from-the-Command-Line and ­http://learnmeabitcoin. com/guide/transactions. 122 Chapter 4 Bitcoin Wallets and Transactions B itcoin Wallet In Chapter 2, you queried a wallet’s available funds via the getbalance command, and you created a new bitcoin wallet utilizing the getnewaddress command. In Chapter 3, you created your very own blockchain wallet for your blockchain; you did so by creating a wallet.js file utilizing the Elliptic Curve Cryptography Node.js library and generating a private-public key combo that you then were able to expose using a CLI. In this section, I will expand on this knowledge by looking at bitcoin’s core and how wallets and transactions are generated. Bitcoin allows users to send and receive coins. A user can generate a wallet, which holds a public key, and the sender will send the coins to the receiver’s wallet’s public key address. Sending coins follows the same process but in reverse. The receiver provides the sender with a wallet’s public key address where they expect to be paid, and the sender sends coins to that public key address. The wallet address is the public key that was generated by the public/private key hashing algorithm. The receiver can generate a new public key every time the user expects payment. Users who don’t need to be anonymous can use just one public key for multiple transactions; however, bitcoin’s original vision encourages users to give a different public key for each transaction, as well as set many private keys that correspond with many public keys. The private keys are stored in a wallet, and each public key represents a wallet address. 123 Chapter 4 Bitcoin Wallets and Transactions reate a Legacy Wallet Address and Retrieve C Private Keys The most common bitcoin address and the type you generated in Chapter 2 is called a Pay to PubKey Hash (P2PKH) address. P2PKH is the public key, and the public key address gets hashed by an algorithm. Bitcoin also supports the P2SH-SEGWIT protocol, which I will discuss later in this chapter. Note Segregated Witness (SegWit) was an addition to bitcoin core code via a soft fork that increased bitcoin’s block size limit by removing the signature data that unlocks the transaction. When the unlocking code is removed, the additional space is used to include more transactions in the chain. To generate an address with P2SH-SEGWIT and P2PKH support, just run the following: > bitcoin-cli getnewaddress 2N96AMUEX4VMNTApPAbUaA6wzP4V9QrbveK To generate the P2PKH address, you will be using the legacy flag. > bitcoin-cli getnewaddress “” legacy 13oWKiVQ7C5Ewwjv6KRpP3Xm5YstzqFixT As you can see, the commands return the public keys. The wallet’s private keys can be viewed via dumping the keys into a file, as you did previously, or just by using the dumpprivkey command. > bitcoin-cli dumpprivkey “13oWKiVQ7C5Ewwjv6KRpP3Xm5YstzqFixT” L5gDpFvfEkUSFeMSQb92kueD1BuX4JeZLAhQkXoEtjcZMog3uXB4 124 Chapter 4 Bitcoin Wallets and Transactions Private keys should not be shared with anyone, as they unlock the funds associated with the public address. With that said, I am sharing this one with you here as a learning example. Note  Protect your private keys. If your private keys are lost, you lose your coins/funds. As you know, you are able to dump the private keys into a text file. > bitcoin-cli dumpwallet ~/mywallet.txt { “filename”: “/Users/Eli/mywallet.txt” } Then, you can get the location of the wallet and can view your keys. > vim /Users/[location]/mywallet.txt The data file you saved contains not only the public and private keys but also transactions related to your wallet. Another useful RPC feature, as you might recall, is that you can query the bitcoin daemon for a specific wallet’s funds. > bitcoin-cli getbalance 1Mr2G632PfQuq4uJXRBNWLoRKH71Qwor51 To get the available funds in your wallet, you just run the getbalance command, which returns a 0 balance because you have not deposited any funds yet. > bitcoin-cli getbalance 0.00000000 125 Chapter 4 Bitcoin Wallets and Transactions ay to Witness a Public Key Hash (P2WPKH): P SegWit Soft Fork Bitcoin (BTC) and bitcoin cash (BCH) have hard-forked mainly over a disagreement of the block size, meaning how much data can be included in each block. In 2017, bitcoin core code was hard-forked into bitcoin cash and allowed to increase the block’s size limit. In 2019, bitcoin cash forked once again because of a dispute over several new features for each fork. The block size limitation in bitcoin means transactions sometimes have to wait to be included in a block; however, because of the 1 MB limitation, they might not be included in the next block, causing slow transaction times when there too many transactions in the network, resulting in an increase of miner fees. To correct this, bitcoin open source developers created a soft fork and included Segregated Witness (SegWit). SegWit increased bitcoin’s block size limit by removing the signature data that unlocks the transaction. When the unlocking code is removed, the additional space can be used to include more transactions in the chain. This method increases the block size to 4 MB. Note SegWit is a process where the block size limit on a blockchain is increased by removing the signature data from bitcoin transactions. This process frees up space and allows you to add more transactions. SegWit uses a Bech32 address defined in BIP173. It is 90 characters and consists of a human-readable part, separator, and data. The unlocking validation code is the witness data. You can say that the new code “segregated the witness.” That’s where the name came from. In the build we are using, v17.0, there is a Witness Public Key Hash option in a wallet and transaction to replace the scriptSig parameters and check the transaction validity. The old legacy code still works, as this is a soft fork. 126 Chapter 4 Bitcoin Wallets and Transactions You have seen this in the getaddressinfo command, which includes both scriptPubKey to support the legacy addresses as well as iswitness. You can run the getaddressinfo command and see these parameters. > bitcoin-cli getaddressinfo $address1 Prior to bitcoin core v0.16, you would have had to use the addwitnessaddress command to turn a legacy address into a P2WPKH. Since bitcoin core v0.16.0, an address accommodates both P2SH and P2WPKH. Thus, the wallet is a P2SH-P2WPKH. If you are using v0.18, you can see that getaddressinfo addresses have both parameters for legacy scriptSig and for SegWit. Elliptic Curve Digital Signature Algorithm Bitcoin core allows you to create a signature by utilizing the Elliptic Curve Digital Signature Algorithm (ECDSA). This can be achieved by utilizing the signmessage command. Adding a signature allows you to prove that you own the private keys of the wallet and thus adds another security layer for the sender to ensure they are sending the funds to the correct address. > bitcoin-cli signmessage “13oWKiVQ7C5Ewwjv6KRpP3Xm5YstzqFixT” “John Doe” This command outputs a hash: HzicuTXMl1COVh7Xw9ky9A/cl7ZjMSWNH10Y/invAgHWa74gS8EOvio3FJkofpH 0nunIA7pJoGwWLRa0UdD7dc8= The sender can verify the wallet prior to sending the funds. > b itcoin-cli verifymessage “13oWKiVQ7C5Ewwjv6KRpP3Xm5YstzqFixT” “HzicuTXMl1COVh7Xw9ky9A/cl7ZjMSWNH10Y/invAgHWa74gS8EOvio3FJk ofpH0nunIA7pJoGwWLRa0UdD7dc8=” “John Doe” 127 Chapter 4 Bitcoin Wallets and Transactions The verify command will output a true or false response. In this case, it will respond with this: true This allows users to confirm they actually own a wallet. This is useful, for instance, on the code level, because the P2PKH address will be utilizing the private key to generate a signature. A P2PKH address is a hash of the public key corresponding to the private key that made the signature. Note ECDSA is the cryptographic algorithm utilized by bitcoin to ensure ownership of funds. It is used to generate the public/private keys and can also include the signature in the algorithm. The ECDSA signature can be checked against up to four possible ECDSA public keys. These public keys will be reconstructed from the signature hash; each key is hashed and compared against the P2PKH wallet address provided for a match. The result is either true or false. As you saw earlier, the example received a true once you ran the verifymessage command. Note  QR code is an image representation of a string. QR readers are used for things such as reading URLs or encoding a wallet’s public key address. You can generate QR code via the Chart Google API: For instance to generate a QR code for address: 13oWKiVQ7C5Ewwjv6KRpP3Xm5YstzqFixT in the amount of 0.00016 BTC you would generate the following URL:×250&cht=qr&chl= bitcoin:13oWKiVQ7C5Ewwjv6KRpP3Xm5YstzqFixT?&amount=0.00016. See Figure 4-1. 128 Chapter 4 Bitcoin Wallets and Transactions Figure 4-1.  Bitcoin QR code via Transactions In this section, I will cover transactions. You will learn how to send coins with bitcoin’s daemon on a testnet utilizing both the command line and the bitcoin core wallet GUI. You will learn how to use the bitcoin explorer to view your transactions. Then I will cover more advanced creation of transactions by showing how to create a raw transaction with one output as well as more complex transactions with utilizing Multisignature (multisig), which is requesting more than a single key to authorize a transaction. Additionally, I will cover how to change other options such as replacing a transaction for a change of fee as well as setting a locktime. You will learn the difference between P2PKH and P2SH-SEGWIT. Lastly, you will learn how to attach other data than just coins with bitcoin using OP_RETURN params. Let’s get started. 129 Chapter 4 Bitcoin Wallets and Transactions S imple Command The first transaction in a block is called the coinbase transaction; this transaction consists of the transaction fees paid by transactions included in the block. To send a transaction, you need to pay a transaction fee to the miners. If there is a low fee or no fee is paid, the transaction may get stuck for a long period of time or even forever in the P2P network until the fee is changed. To set the transaction fee, you can add a parameter to the bitcoin. conf file with a default fee. First, you need to find the file location. To do so, right after you run the daemon, you can track down the location of the file. > bitcoind -printtoconsole After a few seconds, stop this service by pressing Control+C. The command shows the bitcoin.conf file location. It returns the location of the configuration file. Then you can open the file and modify it by adding the default fee. In this case, it was nested inside the Application Support folder. /Users/[my user]/Library/Application Support/Bitcoin/bitcoin.conf When you open the file, you can see that the default transaction fee is set to 0.00000020 (mintxfee=0.00000020). Note  There are other fees and settings in bitcoind. You can modify transactions you send (paytxfee), maximum total fees (maxtxfee), fallback fees, and so on. Visit this bitcoin page for all the available options: Monitor and updating the bitcoin transaction fee can ensure the funds being sent get changed by market forces. There are web sites, apps, and forms that can try to predict the fee that needs to be paid. There are many 130 Chapter 4 Bitcoin Wallets and Transactions sites that help calculate transaction fee prediction, such as this API, that you can call from your code: The API returned at the time of writing a fee of 20 satoshis. {“fastestFee”:20,”halfHourFee”:20,”hourFee”:18} Another example is This site shows a majority of transactions are at five to six satoshis at less than six hours, or 49 to 50 satoshis for less than 20 minutes at the time of writing. Note A satoshi is a hundredth of a millionth BTC and is named after Satoshi Nakamoto. It’s the smallest fraction of a bitcoin that can be sent: 0.00000001 BTC. A faster fee would be 50 satoshi at the time of writing. Now that you know the fee, you can modify the config file with the minimum fee to a higher fee such as 50 satoshis. > vim ‘/[location]/bitcoin/bitcoin.conf’ mintxfee=0.00000050 txconfirmtarget=3 The mintxfee value sets a minimum transaction fee of 50 satoshis, or 0.00000050 ฿. That will set a 20 satoshis/byte of data in your transaction. This means the floating fee needs to figure out a good amount to get the transaction into the next three blocks. As you recall, each block takes about 10 minutes to hash, so it will aim at 30 minutes to include your transaction. Once you have modified the config file, remember to restart bitcoind. > bitcoind -printtoconsole 131 Chapter 4 Bitcoin Wallets and Transactions T estnet In this section, you will learn more about transactions, and to understand transactions better, you will need to send and receive bitcoins. To get bitcoins on mainnet (the actual production chain), you would need to either mine coins or trade them. However, you don’t want to handle actual coins as you learn, because you would have to pay fees as well as risk losing coins if you make mistakes. Also, the price of the bitcoin may go down. Luckily, bitcoin offers an alternative blockchain that is used for testing; it’s called testnet. This alternative blockchain enables you to experiment without using real bitcoins or abusing the bitcoin chain. You can start a bitcoin core instance with the -testnet flag. On testnet, this is done through faucets, the pretend coins. You connect to the testnet blockchain instead of the main blockchain by stopping the bitcoin core demon and restarting it with the testnet flag. > bitcoind -testnet Keep in mind that just as with bitcoin’s mainnet chain, the syncing and indexing portions may take hours, depending on your Internet connection. Run the command and take a long coffee break if you want to start working with blocks. The BTC testnet offers you free faucet bitcoins that you can use for testing. Testnet requests that you return these coins once you complete testing as this service is free, and returning these coins will benefit the next developer who needs them. You can read more about testnet here: Testnet. At the time of writing, testnet3 is the latest blockchain used for testing. You will be using, which can be found at https:// However, there are other faucets in 132 Chapter 4 Bitcoin Wallets and Transactions case this one ceases to exist. The first step is to send coins to your wallet. First generate a new P2PKH wallet address using the following command: > bitcoin-cli getnewaddress “” legacy mnMs77edsGV8VKwtB3d7fsnvrNuZ8ECKfh As you can see, the output you receive is the public key that you can use to receive funds. Next, paste that address into, choose “Bitcoin testnet,” verify you are not a robot, and click the “Get bitcoins!” button, as shown in Figure 4-2. Figure 4-2.  Coin testnet faucet, requesting funds for testing Once the coins have been sent to your wallet, you receive a confirmation with the tx number, as shown in Figure 4-3. 133 Chapter 4 Bitcoin Wallets and Transactions Figure 4-3.  Coin testnet faucet, bitcoins have been sent Note  Keep in mind that these faucet testnet sites often go offline, and you may need to find a new faucet testnet site. For your convenience, here is another one that is working at the time of writing: Viewing Transactions on Block Explorer On the testnet faucet, you can monitor the bitcoins that have been sent just as can be done on the maintest production bitcoin’s blockchain. This is done in the testnet Blockchain Explorer; see the “tx” link, as shown in Figure 4-3. As you recall, “tx ID” stands for the transaction ID. Alternatively, you can paste that transaction ID directly into the Block Explorer at See Figure 4-­4. 134 Chapter 4 Bitcoin Wallets and Transactions Figure 4-4.  Viewing transaction information on live. In fact, every transaction that ever occurs on the blockchain is publicly available to view by anyone in the Blockchain Explorer; that includes all the transaction data except for the users’ private keys. Although the transaction data is publicly available, the identifying information about the owner is not public information and is not needed to perform transactions. What connects the user to the coins you send is the private key associated with the public key. Similarly, you can do the same check of information via the RPC command line. You already know how to check your wallet’s balance, as shown here: > bitcoin-cli getbalance 0.0000000 When coins have been received, they will not be available to spend until the transaction has been confirmed by the mined blocks’ confirmations. That’s why if you check your balance right away, it will still show 0. 135 Chapter 4 Bitcoin Wallets and Transactions You will be able to see the coins as unconfirmed via the getunconfirmedbalance command right after your transaction is included in the next block. To check, run the getunconfirmedbalance command. > bitcoin-cli getunconfirmedbalance 0.10413028 Once you have enough confirmations, the getbalance command will show your new balance, and getunconfirmedbalance will show 0. Similarly, you can be more specific and request the minimum confirmations to be 2. > bitcoin-cli getbalance “*” 2 Note A transaction stays “unconfirmed” until the next new block is created. Once the new block is created, the new transaction is verified and included in that block. Now, the transaction will have one confirmation. About ten minutes pass, and a new block is created, and the transaction is confirmed again. Each confirmation increases the safety of the transaction, and the chances of the transaction being reversed decrease. The norm on exchanges is that four to six confirmations are required to allow you to use the coins; it may be wise to wait for even sixty confirmations for large amounts of coins, which takes about ten hours. Another useful command is the listtransactions command; it provides the full list of transaction data related to your wallet. > bitcoin-cli listtransactions [ { “address”: “mnMs77edsGV8VKwtB3d7fsnvrNuZ8ECKfh”, “category”: “receive”, 136 Chapter 4 Bitcoin Wallets and Transactions “amount”: 0.10413028, “label”: “”, “vout”: 0, “confirmations”: 420, “blockhash”: “0000000000125d2714882704562c8442a6700c58a41ca d0b4108305474be3bb1”, “blockindex”: 4, “blocktime”: 1541783585, “txid”: “645a34a5cbdd66b126e6f81560dc79957c6e1a175a68f8ad23 ca7fd38046df85”, “walletconflicts”: [ ], “time”: 1541783585, “timereceived”: 1541890511, “bip125-replaceable”: “no” } ] ending Testnet Coins via the Bitcoin S Core Wallet GUI You initialized a bitcoin core instance with the testnet flag; however, there is another even easier way to send and receive coins. Bitcoin core includes a GUI wallet you can use. You will be utilizing the GUI software that comes out of the box with bitcoin core. To get started, terminate the bitcoind daemon in Terminal by pressing Control+C and then run bitcoin-qt in a command-line terminal with the testnet flag so you connect to testnet and not mainnet. > bitcoin-qt -testnet 137 Chapter 4 Bitcoin Wallets and Transactions This command opens a new window and then syncs with the testnet blockchain. Just as before, if you did not complete a testnet sync, it may take hours, depending on your Internet connection, as shown in Figure 4-­5. However, at the wallet GUI, you will see an estimated time for how long the sync will take. Figure 4-5.  Bitcoin wallet testnet GUI sync with testnet network As before, you need to wait for the sync to complete; only then can you retrieve your wallet’s public key address and spend your coins. In the Overview menu you will see the balances, including the confirmed (Available) funds and the unconfirmed (Pending) funds. You can also get a list of transactions by clicking the Transactions button at the top. See Figure 4-6. 138 Chapter 4 Bitcoin Wallets and Transactions Figure 4-6.  Bitcoin core wallet overview screen To create a new wallet’s public key address, click Receive at the top and then click the Request Payment button. This will generate an address for your wallet, as shown in Figure 4-7. 139 Chapter 4 Bitcoin Wallets and Transactions Figure 4-7.  Bitcoin core wallet, receive coins screen As you can see, the GUI created a QR code for your convenience. You can scan it when you send coins, where this feature is supported. Now, let’s go ahead and send some more coins to your wallet via the testnet faucet at As you can see, you can then receive coins just as you did via the command line. Next, you will send some coins. You will be sending 0.01 BTC back to the testnet faucet for other developers to use. To do so, click the Send button at the top of the GUI and paste in the testnet faucet wallet address that was provided to you when you sent coins to your wallet. Notice that there is a Choose button next to Transaction Fee in the bitcoin core wallet GUI. This allows you to select the fee, as well as the 140 Chapter 4 Bitcoin Wallets and Transactions number of confirmations. It also includes a way to enable a “replace by” fee. This feature allows you to change the fee in case the fee is too low and the transaction is not getting included in the block. See Figure 4-8. Figure 4-8.  Bitcoin core wallet send screen The testnet faucet sends coins to the wallet address you provided. When you send and receive coins, you get a notification pop-up from the GUI and an updated balance on the overview screen. Click the Transactions button to see the transaction’s information. You can also click each transaction to see the actual transaction data. This is similar to what you saw with the listtransactions command. See Figure 4-9. 141 Chapter 4 Bitcoin Wallets and Transactions Figure 4-9.  Bitcoin core wallet transaction Raw Transaction So far you have received one transaction into your wallet via the command line as well as coins using the bitcoin core GUI. You also were able to view confirmations, the fees balance, and transactions. If you send funds back to the testnet faucet and receive coins, things are simple. This is called a one-input, one-output transaction, as you have one sender and one receiver, and you spent the same amount you received (minus the fees). In real life, transactions can become more complex as there are many use cases where there are one input and multiple outputs or multiple inputs and multiple outputs. Bitcoin core provides you with sets of commands to access a raw transaction (RawTransaction) so you can have more granular control over your transaction. You will start with the simple one-input, one-output transaction via the RPC command line. 142 Chapter 4 Bitcoin Wallets and Transactions Note  Creating and understanding RawTransaction is useful for building software, as you have full granular control over your transaction. However, making mistakes can result in a catastrophic outcome and loss of coins, so use caution and double-check everything before sending any funds. When you receive a transaction, the transaction stays in a state called unspent transaction output (UTXO) in your wallet. To send a one-input, one-output transaction, you need your amount to be equal to the funds you want to send. You can then generate a new UTXO for the receiver you are sending the coins to. The receiver can use these UTXOs to send transactions to a new receiver or receivers, and this process can continue endlessly. Note A UTXO is an individual incoming coin transaction in your wallet. When you receive multiple transactions to one or multiple wallets’ addresses, each stays as a UTXO, so you will have multiple UTXOs. To create a new outgoing transaction, you collect one or more UTXOs as needed depending on how much you are trying to send. Now, what if your UTXO includes a larger amount than you would like to spend? Then you would need to send the remaining of the coins back to your wallet. To get a list of unspent coins, you can use the listunspent command. Close the bitcoin core GUI wallet via Control+C and start the daemon again with the testnet flag. > bitcoind -testnet 143 Chapter 4 Bitcoin Wallets and Transactions When you run the getbalance command, you get your wallet’s balance, which includes the two transactions you received from https:// less the transaction you sent back to the testnet faucet. > bitcoin-cli getbalance 0.18505841 I would like to point out that at any time you can use the -named flag instead of using order arguments. The named argument is useful to ensure you are not making mistakes when working with mainnet. For instance, a getbalance command with the named argument would look as follows: > bitcoin-cli -named getbalance minconf=2 0.18505841 Next, let’s take a look at the listunspent command. As the name suggests, it returns JSON with transactions for coins you did not spend, in other words, your UTXOs. The listunspent command also returns JSON with a variable called vout, which represents the index number of the output in a transaction. Note The vout value represents the index number of the output of a transaction. You will be using a txid and a vout to select the existing output as the input of a new transaction. > bitcoin-cli listunspent [ { “txid”: “50e91c9b73a90bd883f4a9a8a51be729770df20fae0445a 9090b80a8621f4538”, “vout”: 0, 144 Chapter 4 Bitcoin Wallets and Transactions “address”: “2N67MKgL5rYcbuySDFUdypU5DvKjmwZoYEb”, “label”: “”, “redeemScript”: “0014c27b4e6bd8eb821ee80a239e0edd59070f 57233d”, “scriptPubKey”: “a9148d1c6e108c60cfdfa61565ac328be66245 91404b87”, “amount”: 0.09092813, “confirmations”: 17, “spendable”: true, “solvable”: true, “safe”: true }, { “txid”: “be05d068d1245f1c60ea4229c00eb5e96f2a5c5527f1deb7c6 de5e1e20a4b4db”, “vout”: 1, “address”: “2MveVhMe6PTzuhsJHx5zXAjDBwQvzdyqGjM”, “redeemScript”: “00142e29123ba343c577ab9517ede9b74f047d2c2ea3”, “scriptPubKey”: “a914254f0e95fb26c0f29975f866e69543519bf5 65e787”, “amount”: 0.09413028, “confirmations”: 16, “spendable”: true, “solvable”: true, “safe”: true } ] These UTXOs show you a property called txid, which is included in bitcoin’s blocks. The txid property allows you to track transactions, as you saw via the Blockchain Explorer. 145 Chapter 4 Bitcoin Wallets and Transactions Notice that the index starts at 0, and because you have two transactions, it is now 0 and then 1. If you had more transactions, this index would continue. Figure 4-10 illustrates the listunspent result if you have two UTXOs. Figure 4-10.  vout index illustration You can get all the data regarding the transaction via the getrawtransaction command. Here I picked the first tx property from the UTXO you received, and then I added the 1 flag to decode the hex-encoded transaction data; take a look at the command and entire output, shown here: > bitcoin-cli getrawtransaction 50e91c9b73a90bd883f4a9a8a51be729770df20fae0445a9090b80a862 1f4538 1 { “txid”: “50e91c9b73a90bd883f4a9a8a51be729770df20fae0445a9090b 80a8621f4538”, “hash”: “e420b350f5b95e29f51b722a5bd44ea2e9d27a7239d2 e17da02f28e04c757b14”, 146 Chapter 4 Bitcoin Wallets and Transactions “version”: 2, “size”: 248, “vsize”: 166, “weight”: 662, “locktime”: 1443113, “vin”: [ { “txid”: ­”2645c128d68194640a7207eeae6ea42e8e528bcba2369 eec0ba572566228b507″, “vout”: 0, “scriptSig”: { “asm”: “00143bfa0326c076fa6cab0d23aea170bac38ac9a164”, “hex”: “1600143bfa0326c076fa6cab0d23aea170bac38ac9a164” }, “txinwitness”: [ “3045022100fb7f0fc2cf99c8174eb3d14169e1c206157d434d 8290b2efbefa5a37d0773923022065f0b671c0596816c062b9bdc7 b30931edfd99a846a0f1633d301bfb7c03db3c01”, “02d208ff6da0583b99392d30e33c5a12da61b9d9de4c35bb0 d20c33ba3bfc49302” ], “sequence”: 4294967294 } ], “vout”: [ { “value”: 0.09092813, “n”: 0, “scriptPubKey”: { “asm”: “OP_HASH160 8d1c6e108c60cfdfa61565ac328be66 24591404b OP_EQUAL”, 147 Chapter 4 Bitcoin Wallets and Transactions “hex”: “a9148d1c6e108c60cfdfa61565ac328be6624591404b87”, “reqSigs”: 1, “type”: “scripthash”, “addresses”: [ “2N67MKgL5rYcbuySDFUdypU5DvKjmwZoYEb” ] } }, { “value”: 1453.63689543, “n”: 1, “scriptPubKey”: { “asm”: “OP_HASH160 f4eb3fe1578076853a774d36f193684f86f 71d5f OP_EQUAL”, “hex”: “a914f4eb3fe1578076853a774d36f193684f86f71d5f87”, “reqSigs”: 1, “type”: “scripthash”, “addresses”: [ “2NFaEgWoTNL5akkTuGtYQhzTvWhUaCbxBtL” ] } } ], “hex”: “0200000000010107b528625672a50bec9e36a2cb8b528e2ea46 eaeee07720a649481d628c1452600000000171600143bfa0326c 076fa6cab0d23aea170bac38ac9a164feffffff02cdbe8a00000 0000017a9148d1c6e108c60cfdfa61565ac328be6624591404b8 747e059d82100000017a914f4eb3fe1578076853a774d36f1936 84f86f71d5f8702483045022100fb7f0fc2cf99c8174eb3d1416 9e1c206157d434d8290b2efbefa5a37d0773923022065f0b671c 0596816c062b9bdc7b30931edfd99a846a0f1633d301bfb7c03d 148 Chapter 4 Bitcoin Wallets and Transactions b3c012102d208ff6da0583b99392d30e33c5a12da61b9d9de4c3 5bb0d20c33ba3bfc4930229051600”, “blockhash”: “00000000000000321b56aece3932b187927ac3e7d c4532f8811aa612bcfa639a”, “confirmations”: 17, “time”: 1542029870, “blocktime”: 1542029870 } Notice that you have information about the block, confirmation, in, out, and much more. Generating Raw Transactions with One Output Transactions can get complicated easily because there is often a need for more than one input or more than one output. For instance, if you want to send the unspent coins back to your wallet, as well as send coins to multiple addresses, it starts to get complicated. Using RawTransaction, you get full access to where the coins go and are able to achieve complex transactions. You will start by creating a simple RawTransaction by sending one UTXO from one wallet to another. Previously, you sent coins back to the testnet faucet via the bitcoin core wallet GUI. Let’s do the same thing but with the RawTransaction command. To get started, let’s confirm your wallet’s balance prior to sending coins. > bitcoin-cli getbalance 0.18505841 Next, let’s pick the UTXO you will be using to fund the transaction. As you recall, you can get a list of UTXOs, via the listunspent command, and then look at the JSON response and pick the transaction txid. Pick 149 Chapter 4 Bitcoin Wallets and Transactions a transaction that has enough funds to feed your new transaction and a transaction that has been confirmed. > utxo_txid=”50e91c9b73a90bd883f4a9a8a51be729770df20fae0445a909 0b80a8621f4538″ As you probably recall, vout is the index number for an output in a transaction. In this example, I will be pointing to a vout and generating a new transaction. The new transaction can include multiple other vouts, as illustrated in Figure 4-11. Figure 4-11.  vout new transaction illustration In this example, you will set the first index for vout. > utxo_vout=”0″ The last but most important variable you need to set is the recipient address. Here, you will be using the same wallet address as you used previously to send your coins. > recipient=”mv4rnyY3Su5gjcDNzbMLKBQkBicCtHUtFB” 150 Chapter 4 Bitcoin Wallets and Transactions Lastly, you can use the echo command to verify and double-check that you set your variables correctly. > echo $utxo_txid > echo $utxo_vout > echo $recipient Now that you have your variables set, you can generate a RawTransaction object via the createrawtransaction command. You do that by including all the variables you set and declaring the amount you would like to spend. You are using, but you need to use the UTXO less the fee you would like to pay to send the entire coins you have in the UTXO. > rawtxhex=$(bitcoin-cli createrawtransaction “‘[ { “txid”: “‘$utxo_txid'”, “vout”: ‘$utxo_vout’ } ]”‘ “‘{ “‘$recipient'”: }”‘) Next, you can extract the rawtxhex value. > echo $rawtxhex 020000000138451f62a8800b09a94504ae0ff2 0d7729e71ba5a8a9f483d80ba9739b1ce9500000000000ffff ffff0140420f00000000001976a9149f9a7abd600c0caa03983 a77c8c3df8e062cb2fa88ac00000000 The rawtxhex value includes your new transaction information as a hex-encoded data. The following decoderawtransaction command will return some JSON output with decoded data for your transaction: > bitcoin-cli decoderawtransaction $rawtxhex { “txid”: “91d4e108f8957251d2997e1f8dcdd0eec97192e8accf85a9e81 f772f586118af”, 151 Chapter 4 Bitcoin Wallets and Transactions “hash”: “91d4e108f8957251d2997e1f8dcdd0eec97192e8accf85a9e81 f772f586118af”, “version”: 2, “size”: 85, “vsize”: 85, “weight”: 340, “locktime”: 0, “vin”: [ { “txid”: “50e91c9b73a90bd883f4a9a8a51be729770df20fae0445a9 090b80a8621f4538”, “vout”: 0, “scriptSig”: { “asm”: “”, “hex”: “” }, “sequence”: 4294967295 } ], “vout”: [ { “value”: 0.01000000, “n”: 0, “scriptPubKey”: { “asm”: “OP_DUP OP_HASH160 9f9a7abd600c0caa03983a77c 8c3df8e062cb2fa OP_EQUALVERIFY OP_CHECKSIG”, “hex”: “76a9149f9a7abd600c0caa03983a77c8c3df8e062cb2fa 88ac”, “reqSigs”: 1, “type”: “pubkeyhash”, “addresses”: [ 152 Chapter 4 Bitcoin Wallets and Transactions “mv4rnyY3Su5gjcDNzbMLKBQkBicCtHUtFB” ] } } ] } As you have seen, to create a transaction, you generate a signature from the wallet’s public hash and the private key hash. The transaction output script takes the public key and the signature and checks to see whether you have a match to the public key hash. If results are true, you are able to spend the coins; otherwise, you can’t. Note A public key visible in the transaction is a type of transaction called Pay to Pubkey (P2PK). A hidden public key as you have been using is a type of transaction called Pay to PubKey Hash (P2PKH). You will sign your transaction via P2PKH to match your wallet’s type. There are two ways to sign the transaction; you can use signrawtransactionwithkey or signrawtransactionwithwallet. These two signed methods are available in 0.18.0 RPC, including inputs for raw transactions in a serialized hex-encoded format. The signrawtransactionwithwallet command format is as follows: signrawtransactionwithwallet “hexstring” ( [{“txid”:”id”,”vout”: n,”scriptPubKey”:”hex”,”redeemScript”:”hex”},…] sighashtype ) Notice that the signrawtransactionwithwallet command allows you to include a second argument called “prevtxs”. “prevtxs” is formatted as an array that includes the previous transaction outputs. If you decide to utilize and insert value for “prevtxs” the transaction will depends on the previous transaction that may not even be in the blockchain yet. In case you don’t need this feature just set “prevtxs” to null. 153 Chapter 4 Bitcoin Wallets and Transactions The signrawtransactionwithkey command format is as follows: signrawtransactionwithkey “hexstring” [“privatekey1”,…] Notice that the second argument is a base58-encoded array of private keys that will be the only keys used to sign the transaction. The third optional argument is an array of previous transaction outputs that this transaction depends on but may not yet be in the blockchain. In our case, you will not include the second argument because your transaction does not need to depend on other conditions. > bitcoin-cli signrawtransactionwithwallet $rawtxhex { “hex”: “0200000000010138451f62a8800b09a94504ae0ff20d7729e71ba 5a8a9f483d80ba9739b1ce9500000000017160014c27b4e6bd8eb 821ee80a239e0edd59070f57233dffffffff0140420f0000000000 1976a9149f9a7abd600c0caa03983a77c8c3df8e062cb2fa88 ac0247304402205cc4b04859e34aa6b1e924745f33a7643fbe45 fcd6e900fdaa29281feae3f8f6022059d4083a3cf81c3bb8226 7931660afb8ffc4bae87ede8dfa11efcb6af6a14ac90121028 926735fcd5bf6580e6f669c240da8975dddf23a6d4015e 4e0bc1ca3f1d2b7f100000000”, “complete”: true } The previous command returned signed, hex-encoded data in the JSON response. Use that data to set the hex for the signedtx variable. > signedtx=”0200000000010138451f62a8800b09a94504ae0ff20d7729e71 ba5a8a9f483d80ba9739b1ce9500000000017160014c27b4e6bd8eb821ee8 0a239e0edd59070f57233dffffffff0140420f00000000001976a9149f9a7 abd600c0caa03983a77c8c3df8e062cb2fa88ac0247304402205cc4b04859 e34aa6b1e924745f33a7643fbe45fcd6e900fdaa29281feae3f8f6022059d 4083a3cf81c3bb82267931660afb8ffc4bae87ede8dfa11efcb6af6a14ac9 154 Chapter 4 Bitcoin Wallets and Transactions 0121028926735fcd5bf6580e6f669c240da8975dddf23a6d4015e4e0bc 1ca3f1d2b7f100000000″ That’s it; you can now send your transaction via the sendrawtransaction command. > bitcoin-cli sendrawtransaction $signedtx ff75dbb08da6f4dc6463dd32d8f9b1a4781e1eeee338e93e8282 0d0fdfbd43ff The output gets you a txid response that you can check in the Blockchain Explorer as you did before. You can also verify that the funds were removed from your account via the getbalance command. > bitcoin-cli getbalance 0.09413028 As well as listunspent command. > bitcoin-cli listunspent [ { “txid”: “be05d068d1245f1c60ea4229c00eb5e96f2a5c5527f1de b7c6de5e1e20a4b4db”, “vout”: 1, “address”: “2MveVhMe6PTzuhsJHx5zXAjDBwQvzdyqGjM”, “redeemScript”: “00142e29123ba343c577ab9517ede9b74f047d 2c2ea3”, “scriptPubKey”: “a914254f0e95fb26c0f29975f866e69543519b f565e787”, “amount”: 0.09413028, “confirmations”: 86, “spendable”: true, “solvable”: true, 155 Chapter 4 Bitcoin Wallets and Transactions “safe”: true } ] Additionally, you can view the transaction via the listtransactions command. > bitcoin-cli listtransactions [ … { “address”: “mv4rnyY3Su5gjcDNzbMLKBQkBicCtHUtFB”, “category”: “send”, “amount”: -0.01000000, “label”: “”, “vout”: 0, “fee”: -0.08092813, “confirmations”: 1, “blockhash”: “0000000000000016ba1c314375d9bb17b6a857e091fd 4924bda5c9d7d9a2fd15”, “blockindex”: 1, “blocktime”: 1542070705, “txid”: “ff75dbb08da6f4dc6463dd32d8f9b1a4781e1eeee338e93e82 820d0fdfbd43ff”, “walletconflicts”: [ ], “time”: 1542070656, “timereceived”: 1542070656, “bip125-replaceable”: “no”, “abandoned”: false } ] 156 Chapter 4 Bitcoin Wallets and Transactions Transactions that Require Multisignature So far you have been doing standard “single-signature transactions,” as you needed only one signee with one signature to sign a transaction and perform the transfer. However, the bitcoin network supports a more complicated transaction. These transactions can be set to require a signature of multiple signees. For instance, institutions, partners, spouses, or programmed scripts may want to have all parties sign instead of just one. These cases would need all the users’ private keys before funds could be sent. To do a multiple-signees transaction, you will create two separate wallets for testing. You can run bitcoin core on two separate machines and use the RPC calls to generate a new public address for each wallet, or you can download the Electrum wallet at and run it in testnet mode to generate your second wallet. As a first example, you will run Electrum because you can use its built-­ in multisignature wallet to understand this process. Once you complete downloading Electrum, run Electrum as testnet via the command line. > open -n /Applications/ -args -testnet Setting Electrum with a Multisignature Wallet After Electrum starts, select “Multi-signature wallet” for the create wallet option and then click Next. See Figure 4-12. 157 Chapter 4 Bitcoin Wallets and Transactions Figure 4-12.  Electrum multisignature wallet On the next screen, you can select how many cosigners are required and how many signatures are needed. These transactions are often referred to as M-of-N transactions, for instance, a 2-of-3 scenario. A 2-of-3 would mean you need at least two private keys (signatures) from three cosigners to authorize the transaction. You can move the sliders to better understand this feature, as shown in Figure 4-13. Figure 4-13.  Electrum multisignature wallet cosigners and signatures 158 Chapter 4 Bitcoin Wallets and Transactions Here, select a 2-of-2 multisignature wallet, which means two cosigners and two signatures. Then click the Next button. On the following screen, click “Create a new seed” and click the Next button. On the following screen, you can choose the seed type. Standard means P2PKH or SegWit, which means a P2SH-SEGWIT, so select Standard and click Next. For the next step, you are given a seed that represents your private key. Store your seed and be careful not to share it with anyone. You are then provided with what Electrum calls your master public key, and you are asked to share it with your cosigners, as shown in Figure 4-14. Figure 4-14.  Electrum install wizard master public key Note  The Electrum public master key is part of the Electrum Hierarchical Deterministic (HD) wallet that generates an address for you based on a master seed that can be used to back up all your funds. The seed consists of words used to retrieve your wallet’s private keys; losing your seeds would mean losing your private keys. Click Next, and you can enter a cosigner’s public key or private key. See Figure 4-15. 159 Chapter 4 Bitcoin Wallets and Transactions Figure 4-15.  Electrum install wizard cosigner key On the next screen of the wizard, you will be using the master private key of your bitcoin core’s wallet to allow Electrum to sign the second wallet on your behalf. You can retrieve the private key from inside your private key backup file. It shows under extended private masterkey. > vim /Users/[location]/mywallet.txt # extended private masterkey: [key] The Electrum wizard sets your cosigners for you, and the next step of the install wizard asks you to set up your password, if you like, for extra security. That’s it. Now that the wizard has completed setting up your account, you can send and receive funds from and to your cosigner wallet. Click Receive at the top to get your wallet address, as shown in Figure 4-16. Figure 4-16.  Electrum wallet receive address and QR code 160 Chapter 4 Bitcoin Wallets and Transactions You will be using again to fund your new wallet: Then you can send these coins back to the wallet’s address after the coins have been confirmed; here is wallet’s address: 2N7RzS3j2eKHVj1E5yV7iGuwfgUtobrCnrc Since you have been providing both of the cosigner’s private keys, this transaction will be happening using the send command. However, in case you set two accounts and provide only one public key, the second cosigner would need to approve this transaction on his account before the send command will actually send the coins. Similarly, you can do this transaction via the RPC command line. To get started, click File ➤ Delete at the top of Electrum to create a standard wallet instead of a cosigner wallet. Once this wallet is removed, you can start over and create a new Standard (P2PKH) wallet that you will be using as the second cosigner. To retrieve your wallet’s address, click the View link at the top and then click Addresses. Next, right-click an address for which you’d like to see its public key. This will show the address public key. See Figure 4-17. – Here is the example’s wallet address: mxaFFFW5CFfJi6fbhn1qFDi8gv6eFsSBKQ – Here is the example’s public key: 038e6fb8b842c750eb68bfccfd0fa1aa1c e8e455d58137e260a067e6d2fb853ea6 161 Chapter 4 Bitcoin Wallets and Transactions Figure 4-17.  Electrum Standard wallet address and public key Next, you will create a new address for your cosigner via command-­line RPC. > bitcoin-cli getnewaddress 2Msggcttx7wDDbcib6yD8ng2oKRdq8Bz4wV Next, you can set the two cosigners’ addresses. > address1=2Msggcttx7wDDbcib6yD8ng2oKRdq8Bz4wV > address2=mxaFFFW5CFfJi6fbhn1qFDi8gv6eFsSBKQ Ensure the address is correct via the validateaddress command. > bitcoin-cli validateaddress $address2 You need both cosigners’ public keys to create your cosigner wallet. You already have the Electrum wallet’s public key; now you need bitcoin core’s RPC public key. To get this, you use the getaddressinfo command to take a look at the RPC JSON response and pubkey variable. 162 Chapter 4 Bitcoin Wallets and Transactions > bitcoin-cli getaddressinfo $address1 { “address”: “2Msggcttx7wDDbcib6yD8ng2oKRdq8Bz4wV”, “scriptPubKey”: “a91404d0a132b5796d4462f39865d56af4ff7255d1b 287”, “ismine”: true, “iswatchonly”: false, “isscript”: true, “iswitness”: false, “script”: “witness_v0_keyhash”, “hex”: “001440bbb1a949badb3a12a941a44bc994f7127c595c”, “pubkey”: “034ffed96ffc416b90daa97df5c09b618d7fbf99076ed8100 900cfa0890e763ac0”, “embedded”: { “isscript”: false, “iswitness”: true, “witness_version”: 0, “witness_program”: “40bbb1a949badb3a12a941a44bc994f7127c595c”, “pubkey”: “034ffed96ffc416b90daa97df5c09b618d7fbf99076ed81 00900cfa0890e763ac0”, “address”: “tb1qgzamr22fhtdn5y4fgxjyhjv57uf8ck2u4glnj9”, “scriptPubKey”: “001440bbb1a949badb3a12a941a44bc994f7127c5 95c” }, “label”: “”, “timestamp”: 1541782726, “hdkeypath”: “m/0’/0’/9′”, “hdseedid”: “572deaa922cbf31076701942878c3e5fc2e23b60”, “hdmasterkeyid”: “572deaa922cbf31076701942878c3e5fc2e23b60”, “labels”: [ { 163 Chapter 4 Bitcoin Wallets and Transactions “name”: “”, “purpose”: “receive” } ] } Now, you are ready to create your cosigners’ multisigned address via the createmultisig command because you have both cosigners’ public keys. > bitcoin-cli -named createmultisig nrequired=2 keys=”‘[“034ffe d96ffc416b90daa97df5c09b618d7fbf99076ed8100900cfa0890e763ac0”, “038e6fb8b842c750eb68bfccfd0fa1aa1ce8e455d58137e260a067e6d2 fb853ea6”]”‘ { “address”: “2MtBkhgVLJ6VA1nFbjam36iUY1dCiWFf4ix”, “redeemScript”: “5221034ffed96ffc416b90daa97df5c09b618d7fbf99 076ed8100900cfa0890e763ac021038e6fb8b842c 750eb68bfccfd0fa1aa1ce8e455d58137e260a0 67e6d2fb853ea652ae” } Next, you need to pick a UTXO txid and vout to sign your transaction, just as you did in previous raw transactions. > bitcoin-cli listunspent [ { “txid”: “ea3fb46ab103d15120e02ed6b60e3d83b265fed26794e3ed 739496b62445410b”, “vout”: 0, … ] Then you set the utxo_txid property. 164 Chapter 4 Bitcoin Wallets and Transactions > utxo_txid=ea3fb46ab103d15120e02ed6b60e3d83b265fed26794e3ed73 9496b62445410b > utxo_vout=0 > recipient=”mv4rnyY3Su5gjcDNzbMLKBQkBicCtHUtFB” > rawtxhex=$(bitcoin-cli -named createrawtransaction inputs=”‘[ { “txid”: “‘$utxo_txid'”, “vout”: ‘$utxo_vout’ } ]”‘ outputs=”‘{ “‘$recipient'”: 0.001}”‘) Now decode and set the hexstring property. > bitcoin-cli -named decoderawtransaction hexstring=$rawtxhex > bitcoin-cli signrawtransactionwithwallet $rawtxhex { “hex”: “020000000001010b414524b6969473ede39467d2fe65b2833d0eb 6d62ee02051d103b16ab43fea0000000017160014040c578cf60bf 00980bfde1920f54459eaab3a09ffffffff01a086010000000000 1976a9149f9a7abd600c0caa03983a77c8c3df8e062cb2fa88ac0 24730440220603883ace41bdf5cf85c87e80f7362b45e35949114 f46ac5e5b89f5e13d8d95002205c5eb45ca7de8b2da88c41c4311 711beb14e8e0d679e40d1fbc2cb8e81e053fb01210205e848e0f2 2dfe0c428d02c356d0c9a8d064a789a6bbcaa43a245d701948aba 200000000”, “complete”: true } Lastly, sign your transaction via the signedtx command. > signedtx=”020000000001010b414524b6969473ede39467d2fe65b283 3d0eb6d62ee02051d103b16ab43fea0000000017160014040c578cf 60bf00980bfde1920f54459eaab3a09ffffffff01a0860100000000 001976a9149f9a7abd600c0caa03983a77c8c3df8e062cb2fa88ac 024730440220603883ace41bdf5cf85c87e80f7362b45e35949114 f46ac5e5b89f5e13d8d95002205c5eb45ca7de8b2da88c41c43117 165 Chapter 4 Bitcoin Wallets and Transactions 11beb14e8e0d679e40d1fbc2cb8e81e053fb01210205e848e0f22dfe0 c428d02c356d0c9a8d064a789a6bbcaa43a245d701948aba200000000″ You are ready to send your transaction using sendrawtransaction value. > bitcoin-cli sendrawtransaction $signedtx Replaceable Transactions and Locktime When creating a RawTransaction with the createrawtransaction command you can includes two more variables you can utilize: locktime and replaceable. createrawtransaction [{“txid”:”id”,”vout”:n},…] [{“address”:a mount},{“data”:”hex”},…] ( locktime ) ( replaceable ) You can learn more about these arguments here: createrawtransaction/ As the name suggests, replaceable allows a raw transaction to be replaced by a new transaction with higher fees. This happens when the fee you set is too low, causing the transaction not to go through. For instance, if the fee you are trying to pay is too high, you can get the following error message: absurdly-high-fee, 11563419 > 10000000 (code 256) Bitcoin core supports the locktime argument in the raw transaction; this argument allows you to send transactions at some time in the future, and until they’re sent, the sender can cancel the transaction. There are two options. Block height is used for small numbers, and UNIX timestamps are used for big numbers. These arguments mean that the transaction is not inserted into the block until the conditions are met. 166 Chapter 4 Bitcoin Wallets and Transactions Note  Block height is the number of blocks in the chain between any specific block and the first chain block on the chain. Bitcoin Colored Coins Bitcoin transactions hold a property called OP_RETURN. This property can be used to hold up to 80 bytes of data, which can be used for passing data. This may not seem much, but it’s enough for proof of ownership or passing small pieces of data to authenticate. Utilizing the OP_RETURN property is done by setting data code word in the vout property of the transaction. To pass the data we want to include in your transaction, you still need to send funds for the transaction to be included in the blockchain, but you can set the recipient to be your own wallet in case you don’t want to pay someone. That way you get to store data in the Bitcoin persistence Blockchain and you only need to pay the transaction fee as you don’t pay anyone. Note  OP_RETURN is the opcode script that defines the transaction as valid or invalid; it can be used to insert data into the transaction that will result in storing that data in the bitcoin blockchain. Keep in mind that there are different opinions about whether it’s okay to utilize this property. Some believe that storing noncurrency data in the blockchain is a bad idea; because there are less costly and more efficient ways to store data, it really depends on usage. Sending a Transaction with OP_RETURN Before you set your transaction, you will want to introduce a small lightweight utility program called jq to streamline creating a RawTranaction object. This is a command-line JSON processor that you can use to process your RPC JSON in the terminal. You can download it from 167 Chapter 4 Bitcoin Wallets and Transactions Install it with Brew. > brew install jq The jq utility allows you to retrieve pieces of the returned JSON so you will be able to stream your transaction quicker and with fewer mistakes. Next, you can set some data to send via the OP_RETURN param. This example will create an MD5 for a file. In real life, this can be a version of a contract between parties or any piece of code you need. Note  The Message-Digest 5 (MD5) algorithm is a function that generates a 128-bit hash value. It’s common to create a file that holds checksum files and that ensures the integrity of data because each file change would result in a new MD5 result. You can pick one of bitcoin’s core files such as config.log to generate an MD5 hash and set the op_return_data variable. > md5 config.log MD5 (config.log) = 634ef85e038cea45bd20900fc97e09dc > op_return_data=”634ef85e038cea45bd20900fc97e09dc” As you saw previously in this chapter, you can use the listunspent command to select your UTXO that you want to spend. > bitcoin-cli listunspent Now using the jq utility, you can stream the process, so you don’t need to do a copy and paste and can avoid errors. > utxo_txid=$(bitcoin-cli listunspent | jq -r ‘.[0] | .txid’) > utxo_vout=$(bitcoin-cli listunspent | jq -r ‘.[0] | .vout’) > recipient=$(bitcoin-cli getrawchangeaddress) 168 Chapter 4 Bitcoin Wallets and Transactions Notice a few things here. You set the first JSON item [0] here, but you can set any item you want, such as [1] or [2]. Also, notice that you need to run the listunspent command to find out the “amount” the UTXO has. For this example, the amount is 0.1166341, and since you want to pay 0.00000200 for fees (200 satoshis), you will be sending 0.1166321 in total. If you don’t set the fee correctly, you may end up spending too much on fees or getting an error message such as the following: – min relay fee not met, 29 < 161 (code 66) – absurdly-high-fee, 24432219 > 10000000 (code 256) You can use the echo command to ensure your variable is set correctly. Then you can continue and set your transaction’s data. > rawtxhex=$(bitcoin-cli -named createrawtransaction inputs=”‘[ { “txid”: “‘$utxo_txid'”, “vout”: ‘$utxo_vout’ } ]”‘ outputs=”‘{ “data”: “‘$op_return_data'”, “‘$recipient'”: 0.1166321}”‘) Next, you need to sign and send the transaction. > signedtx=$(bitcoin-cli signrawtransactionwithwallet $rawtxhex | jq -r ‘.hex’) > bitcoin-cli sendrawtransaction $signedtx 43a14c3b1ac446e4774c5338e5ae4e23839ab65a38c45da8b790f44 49b090ae5 Now, you can track the RawTransaction object on the testnet Blockchain Explorer ledger, as shown in Figure 4-18. Here’s the URL: 6e4774c5338e5ae4e23839ab65a38c45da8b790f4449b090ae5/ 169 Chapter 4 Bitcoin Wallets and Transactions Figure 4-18.  Block Explorer testnet, transaction with data As you can see in Figure 4-18, you are getting the message “Data Embedded in Transaction with Unknown Protocol.” If you were to design some software that uses this method on a regular basis, you would want to include a keyword to identify your data. Bitcoin’s Colored Coins The colored coins name stuck from bitcoin core’s older implementations of the EPOBC protocol where an asset is associated with satoshis (thus “coloring”). Now you are able to achieve coloring with the OP_RETURN param. OP_RETURN colored your coins and provided a new capability for bitcoin’s blockchain, as you were able to embed data that provided proof of ownership. You can also set other conditions to happen at a specific time or pass data related to the transaction you inserted into the blockchain. OP_RETURN is powerful, and later in this book you will see how OP_RETURN is utilized in production-grade projects to solve all sorts of issues. 170 Chapter 4 Bitcoin Wallets and Transactions Summary In this chapter, you dove deep into the bitcoin core RPC. You generated a legacy and SegWit bitcoin wallets, and you were able to retrieve the wallet’s private keys and better understand the Elliptic Curve Digital Signature Algorithm (ECDSA) and how the public and private keys are created. You spent the majority of this chapter looking into transactions; you sent coins with bitcoin’s daemon on testnet as well as utilizing bitcoin’s core wallet GUI to send coins. After coins were sent, you learned how to view your transactions in bitcoin’s Block Explorer. You continued by looking into RawTransaction and learned how to generate transactions with one output as well as more complex transactions with multiple signers via Electrum as well as the command line. Additionally, you learned other options such as replacing your transaction for a change of fee as well as setting the locktime variable. You learned the difference between P2PKH and P2SH-SEGWIT. Lastly, I covered how to pass data using the OP_RETURN params, which can be used for bitcoin colored coins or just to pass additional data utilizing bitcoin’s blockchain for more than spending coins. In the next chapter, you will take a closer look at Ethereum and how to write smart contracts. 171 Ethereum Wallets and Smart Contracts In Chapter 1, I introduced Ethereum when I covered bitcoin, altcoins, and different consensus mechanisms. Specifically, I covered Ethereum’s PoW consensus and how utilizing Ethereum enables developers to create their own smart contracts and tokens. I mentioned that the Ethereum tokens can be generated as Ethereum requests for comment (ERCs) such as ERC-­20, ERC-223, or ERC-777. In Chapter 3, you created your own blockchain, and I covered bitcoin wallets and transactions. In this chapter, I will be expanding on Ethereum in more detail. Ethereum allows you to create code (smart contracts) to handle funds utilizing blockchain technology to overcome downtime and third-party interference. The Ethereum platform is mostly credited to Vitalik Buterin and Gavin Wood. According to the Ethereum web site, the definition of Ethereum is as follows: “Ethereum is a decentralized platform that runs smart contracts: applications that run exactly as programmed without any possibility of downtime, censorship, fraud or third-party interference.” — Chapter 5 Ethereum Wallets and Smart Contracts In previous chapters, you were able to pass and store data such as the bitcoin colored coins use case with the OP_RETURN param. This is useful because you’re able to generate an MD5 hash of a file and store it on bitcoin’s network. The MD5 you stored could be of a document, a contract, or anything you want. However, as you saw, bitcoin is limited to only storing the information, and you were unable to interact with the data. Specifically, you are able to pass and store data on the network, but you are unable to run code against your file such as to perform operations against your data. Ethereum solves this lack of functionality by allowing you to create a smart contract utilizing the power of blockchain. Note  Smart contracts are programmable code used to handle funds. The code runs on its own, absent of the need of third parties. Solidity is a popular Ethereum contact-oriented programming language and can be used to write smart contracts and deploy the code on multiple blockchains. At the heart of Ethereum is the Ethereum Virtual Machine (EVM). The EVM is where the smart contracts run in Ethereum. A good way to help you understand the EVM is to think about the EVM as a distributed global computer where the smart contracts can be executed. Note  The EVM is a distributed global computer to run arbitrary, algorithmic, complex code. More simply, the EVM consists of all the nodes in the Ethereum network connected as a singular consensus and able to take a smart contract’s code, process it, and execute it. The EVM uses 256 bits as the fundamental consensus mechanism; it can handle a 1 TB block, and the standard block time is 15 seconds. 174 Chapter 5 Ethereum Wallets and Smart Contracts Decentralized application developers write smart contracts and then run the code on the EVM with the help of front-end code. See Figure 5-1. The EVM executes the code in parallel connections on all the connected Ethereum nodes. This ensures the consensus of the nodes. The size of the Ethereum blockchain can be as big as 1 TB at the time of writing versus bitcoin’s block height, which is limited to 4 MB per block. Additionally, bitcoin takes about 10 minutes to create a new block versus 15 seconds on the EVM. Although it is advantageous for the decentralized code to run as a singular consensus, there are also drawbacks. For instance, the smart contract’s code is slower and more expensive than a traditional computer as it runs on all nodes. Figure 5-1.  Ethereum 10,000-foot perspective. Photo credit: To run an Ethereum miner, you need to run a full-node EVM. The miners are running a PoW consensus mechanism to verify transactions just like bitcoin. During the mining process, five coins are mined on every block. Just as you saw with NEO in Chapter 1, the Ethereum miners get paid for running smart contracts with Ethereum coins, which get changed into what is called gas. 175 Chapter 5 Ethereum Wallets and Smart Contracts Note  Ethereum gas is a fraction of an Ethereum token. Ethereum gas is changed and used by the contract to pay the miner for their efforts. Think of a car. It needs gas to operate, and so does Ethereum. Absent Ethereum gas, you cannot execute the smart contract. Because Ethereum offers the ability to build interesting applications, the platform has been acknowledged for its potential and is utilized in one way or another by Microsoft, Intel, Amazon, J.P. Morgan, and even governments. This has turned Ethereum into an extensive ecosystem with many options to choose from to help you create your smart contracts easily. You can choose from a large number of development tools, apps ­communicating with other tools, best practices, infrastructure, testing, security, monitoring tools, and much more. It can be overwhelming and confusing to choose tools to use, especially when many of the tools are still in alpha, beta, or not fully tested. However, keep in mind that by now you are already equipped with a good fundamental understanding of blockchain technologies, including transactions, wallets, and how it all works. Additionally, the blockchain you developed in Chapter 3 was in JavaScript utilizing Node.js, which is fundamental for many Ethereum tools. There are two lists that I recommend you bookmark, listed here: – – These resources provide an extensive list of all the development tools and resources related to Ethereum. It’s beyond the scope of this book to cover all these different tools, but I recommend you review these tools at 176 Chapter 5 Ethereum Wallets and Smart Contracts some point if you focus on Ethereum development so you can make your own determination about which tool fits your project best. In this chapter, I will be focusing on Ethereum smart contracts and running them on a testnet, just as you have done in the previous chapters for bitcoin. I will show how to set up your development tools and IDE and give you basic information for dapp mainnet deployment, which I will expand upon in later chapters in this book. Ganache Simulated Full-Node Client Ganache (previously known as ethereumjs-testrpc) allows you to run a simulated full-node client of Ethereum on your machine and to interact with your contract via a CLI. This tool is useful because you will be setting up a development network and a private testnet network to test your smart contract code. Just as you saw in the previous chapter, setting up a testnet network allows you to test your code with pretend money before committing your code to mainnet. I decided to use Ganache in this chapter as it is part of the Truffle development suite and integrates well with Truffle. I nstall Ganache To get started, you can install Ganache globally with npm and confirm it’s working correctly by calling the help command. > npm install -g ganache-cli > ganache-cli help If you have installation issues or want to get more information regarding the tool, visit the Ganache GitHub page: trufflesuite/ganache-cli. You can also check the version of CLI by running this command: > ganache-cli -v 177 Chapter 5 Ethereum Wallets and Smart Contracts This command outputs the version. At the time of writing, the Ganache CLI is version v6.4.3 (ganache-core: 2.5.5). Ganache CLI: Listen to Port You can run Ganache on your machine while you develop and debug your contracts. To do this, you set up the Ganache CLI in Terminal to listen to the port you will be setting in truffle.js later in this chapter. > ganache-cli -p 8584 Notice that at this point there is nothing running on port 8584, so let’s assume you will be setting up port 8584. The command should output the following: Listening on IntelliJ IDEA Plugin for Solidity In Chapter 3, you downloaded and used WebStorm as your IDE to develop your blockchain. WebStorm is a subset of IntelliJ IDEA and has a plugin for the Solidity language, which provides an easy way to write your contracts. Also, it provides highlights and code completion to make development easier. You can use the WebStorm version you previously installed and just add the Solidity plugin. To do so, first download the plugin here: To get the plugin installed, follow these steps: 1. Select WebStorm ➤ Preferences (or press command + ,). 2. Select Plugins. 3. Search in “Plugins” for “Solidity”. It will say “No Plugins founds.” With a link to “Search in repositories”. Click the “Search in repositories” link. “Intellij-Solidity” plugin will show. See Figure 5-2. 178 Chapter 5 Ethereum Wallets and Smart Contracts 4. Install both “Intellij-Solidity” plugins: LANGUAGES and INSPECTION. See Figure 5-2. 5. Click IntelliJ-Solidity ➤ install. See Figure 5-2. Figure 5-2.  Installing IntelliJ-Solidity and Solidity Solhint in WebStorm 6. Under Plugins search for Solidity Solhint. It will say “No Plugins founds.” With a link to “Search in repositories”. Click the “Search in repositories” link. Click Solidity Solhint INSPECTION ➤ and then click Install. 7. Restart WebStorm. Note that if you are a Visual Studio fan, there is also a Solidity extension for Visual Studio; see items?itemName=ConsenSys.Solidity. At the time of writing, the plugin works only for Visual Studio 2015 or earlier. Keep in mind that, as always, you can use your favorite IDE, text editor, or even vim to write your code; there’s no need to buy an IDE. T ruffle Suite You will be using Truffle as it’s one of the most popular tools and has integrated libraries that help expedite the development cycle. Truffle Suite includes Truffle, Ganache, and Drizzle; see Figure 5-3. 179 Chapter 5 Ethereum Wallets and Smart Contracts “Truffle is a development environment, testing framework and asset pipeline for Ethereum, aiming to make life as an Ethereum developer easier.” — The Truffle documentation includes installation instructions, which can be found at Figure 5-3.  Truffle Suite documentation To get started, open a new Terminal window and install Truffle globally on your machine (at the time of writing, the current Truffle version is 5.0.14). Then ensure it’s installed correctly by running the help command to view a list of all available commands. > npm install -g truffle + [email protected] > truffle help Truffle v5.0.14 – a development framework for Ethereum Usage: truffle [options] 180 Chapter 5 Ethereum Wallets and Smart Contracts Create Your Smart Contracts To get started, let’s create your folder and initialize the Truffle wizard to generate all the code needed to get started. In Terminal, type the following: > mkdir MySmartContract && cd $_ > truffle init These commands create a folder named MySmartContract and change the directory location to the new project; then the truffle init command initializes the project. You can see the output in Figure 5-4. Figure 5-4.  Creating the MySmartContract project and initializing with the truffle init command Next, open WebStorm and open the project you created by selecting File ➤ Open. Navigate to the MySmartContract project directory and click Open. WebStorm will open the project, as shown in Figure 5-5. 181 Chapter 5 Ethereum Wallets and Smart Contracts Figure 5-5.  MySmartContract open in WebStorm EVM supports many programming languages such as Solidity, JavaScript, GO, C++, Python, Java, Ruby, Web Assembly, Rust, and Haskell. In this section, you will be using Solidity as it’s the most popular Ethereum programming language for smart contracts at the time of writing. Solidity is based on ECMAScript and influenced by JavaScript, C++, and Python. Solidity has an advantage as you are able to deploy your smart contract transactions on other various blockchain platforms beside Ethereum, such as Ethereum Classic, Tendermint, ErisDB, and Counterparty. Solidity uses the .sol file extension; in fact, if you check in the contracts folder of your project, you will find a file called Migrations.sol, as shown in Figure 5-5. This file was generated automatically for you when you initialized the Truffle wizard. The migration files help you deploy contracts to the Ethereum network. As your project progresses, you will create new migration files. 182 Chapter 5 Ethereum Wallets and Smart Contracts Connect Truffle to the Ganache Network Next, you will customize your environment by calling your network development and setting the URL and port. As you recall, you are already running Ganache and have programmed your network to listen on, port 8584. You’ll use these settings for deploying your contracts on your Ethereum blockchain network. To get started, open MySmartContract/truffle-config.js and inside the network object add a development object with these configuration settings: module.exports = { networks: { development: { host: “”, port: 8584, network_id: “∗”, gas: 4712388, gasPrice: 100000000000 } } You set the host, port, and network ID, as well as the gas and gasPrice parameters. The following is according to Truffle docs ­( configuration#networks): – gas: This is the gas limit used for deploys. The default is 4712388. – gasPrice: This is the gas price used for deploys. The default is 100000000000 (100 Shannon). You are setting the default values, which you can achieve also by omitting the gas and gasPrice tags; however, for the live mainnet network, at the time of writing, I recommend setting a 21,000 gas price that is a 183 Chapter 5 Ethereum Wallets and Smart Contracts reasonable value. Check the ETH Gas Station (https://ethgasstation. info/) to figure out how much the gasPrice value should be, as shown in Figure 5-6. Figure 5-6. calculates a recommended gas price As you can see, at the time of writing, paying a fiat of $0.014 provides a standard 5.6 transaction time. You have set up a development environment only; however, as you move your code from development to a public testnet network and then production, you can add more environments to the truffle-config.js file. “Hello, World” Smart Contract As mentioned, smart contracts are account objects on the Ethereum blockchain; you can write functions to interact with other contracts, send coins, make decisions, and store data. Generally speaking, the 184 Chapter 5 Ethereum Wallets and Smart Contracts contracts are built to be decentralized; however, keep in mind they can be programmed with a regulated option, making them centralized. For instance, the Ethereum Gemini dollar has the option to freeze transactions or even reverse them, and other coins can be built with a self-destruct function by the owner. You’ll start by creating a simple “Hello, World” contract. This is the minimum code, and the intention here is not to create anything useful but to help you understand how to create a smart contract. In Terminal, at the project location, create a new contract and call it HelloWorldContract using the command truffle. > truffle create contract HelloWorldContract If the CLI worked correctly and without errors, it doesn’t output anything. Next, open the contract you created; it will show up under contracts/ HelloWorldContract.sol. As you can see, the Truffle wizard created your contract for you. This first smart contract is a minimal working example; it just holds a message and allows you to retrieve the message by calling your main function. Replace the existing code in contracts/HelloWorldContract.sol with the following below; pragma solidity ^0.5.0; contract HelloWorldContract { string greeting; constructor() public { greeting = ‘Hello World’; } function greet() public view returns (string memory) { return greeting; } } 185 Chapter 5 Ethereum Wallets and Smart Contracts As you can see, Solidity scripting is similar to JavaScript or C++, and it’s easy to read. The first line of code is the Solidity compiler version; you will be using 0.5.0. In the HelloWorldContract constructor, you are setting the greeting variable to ‘Hello World’. The main function is greet(). Once you call the main function, you can retrieve the value of the greeting ­variable. “MD5SmartContract” Smart Contract Now you will create a second contract that is more practical. This contact will allow you to store the MD5 hash you stored in the previous chapter, but this time you will be able to interact with it instead of just storing the MD5 data on the blockchain. In Terminal, at the project level, create a new contract called MD5SmartContract using the command truffle. > truffle create contract MD5SmartContract Next, open the contract you created called contracts/ RegisterContract.sol. You will be running the following contact: pragma solidity ^0.5.0; contract MD5SmartContract { bytes32 public signature; event signEvent(bytes32 signature); constructor() public { } function sign(string memory document) public { signature = sha256(bytes(document)); emit signEvent(signature); } } 186 Chapter 5 Ethereum Wallets and Smart Contracts The code creates a variable call signature. Then your main function signs your document. You pass the document MD5, and using SHA256, you sign the document. You create an event to get dispatched once you sign your document. Note  Secure Hash Algorithm (SHA) is one of a number of cryptographic hash functions. A cryptographic hash function acts as a signature for text or data; it is one-way and cannot be decrypted. The generated SHA256 hash is a fixed-size, 256 bits (32 bytes), and almost unique. Create Truffle Migration Files for Your Smart Contract Deployment As mentioned, Truffle migration files help you deploy your contracts on the Ethereum network. You will create a migration file for your deployment. To do so, create a new deployment file; call it 2_deploy_ contracts.js, and place the file here: migrations/2_deploy_contracts. js. You can point to the smart contract code you created as follows: const HelloWorldContract = artifacts. require(“HelloWorldContract.sol”); module.exports = function(deployer) { deployer.deploy(HelloWorldContract); }; Create another deployment file, called 3_deploy_contracts.js, and place the file here: migrations/3_deploy_contracts.js. const MD5SmartContract = artifacts.require(“MD5SmartContract.sol”); module.exports = function(deployer) { deployer.deploy(MD5SmartContract); }; 187 Chapter 5 Ethereum Wallets and Smart Contracts At this point, your project includes two smart contracts and migration files. You can compare your project directory and files with mine; see Figure 5-7. Figure 5-7.  MySmartContract including two smart contracts and migration files Another technique for lazier developers is to use the Truffle create wizard to generate the migration file. > truffle create migration deploy_my_contract This command generates the migration file automatically for you. Compile Your Smart Contract with Truffle In a separate Terminal window, you will run Truffle to compile your smart contract. The compile command turns your Solidity code to bytecode, which can be interpreted by the EVM. For now, Ganache simulates the EVM. > truffle compile 188 Chapter 5 Ethereum Wallets and Smart Contracts You can see your contract’s bytecode in the JSON file found here: build/contracts/HelloWorldContract.json and build/contracts/ MD5SmartContract.json. Look for the bytecode tag shown here: “bytecode”: “0x608060405234801561001057600080fd5b5061031…”, Note  Keep in mind that ideally you should delete the contract’s contracts/∗.json file manually before compiling again. This will ensure the latest code gets compiled because the CLI does not always recognize changes right away. eploy the Smart Contract to Your D Development Network Now that you have bytecode compiled from your smart contract, you can migrate the bytecode into your development environment so you can run the migration command to switch to the network you set in the truffle.js file. > truffle migrate -network development Running this command will return the response shown in Figure 5-8. This shows you that three migration files have been deployed successfully on the network. You have a successful deployment for each contract. 189 Chapter 5 Ethereum Wallets and Smart Contracts Figure 5-8.  Truffle migrate command response Keep in mind that the -reset flag is useful when you change your code, as you need to recompile, and re-deploy. > truffle migrate -reset Truffle Console Now that your contract has been deployed to your development network you can communicate with your smart contract via the Truffle CLI. To do so, you can open a console and connect it to your development network. > truffle console -network development Once you run the console command, your Terminal shows you are in Truffle CLI development mode. truffle(development)> To get out of CLI mode, click Control+C twice or type .exit in the console. 190 Chapter 5 Ethereum Wallets and Smart Contracts Interact with Your Smart Contract via the Truffle CLI You set two variables, hello and sign, for your smart contracts so that you can interact with them. truffle(development)> HelloWorldContract.deployed().then(_app => { hello = _app }) undefined truffle(development)> MD5SmartContract.deployed().then(_app => { doc = _app }) undefined To interact with your HelloWorldContract contract, you can call the main public function you created because you exposed the function greet. truffle(development)> hello.greet() ‘Hello World’ Similarly, you can interact with the MD5SmartContract.sol contract. You will pass the same MD5 hash you generated in Chapter 3 (634ef85e038cea45bd20900fc97e09dc) and call your main function called sign. That function will generate an SHA256 hash, as shown in Figure 5-9. truffle(development)> doc.sign(‘634ef85e038cea45bd20900fc97e09dc’) 191 Chapter 5 Ethereum Wallets and Smart Contracts Figure 5-9.  Creating a doc.sign transaction Now you can confirm that you have an SHA256 hash by calling the signature function; see the output in Figure 5-10. truffle(development)> doc.signature() ‘0x7869cd540ff8c3b2635ec87251f361e21ad3c72fbc2f79897b9816 bec54b0a48’ 192 Chapter 5 Ethereum Wallets and Smart Contracts Figure 5-10.  Interacting with the MD5SmartContract smart contract to produce a signature You can download the entire smart contract project from here: C ompile with Remix So far you used the Truffle tools, Ganache network, and WebStorm IDE to create, compile, deploy, and interact with your contract; however, there is another even easier way. Remix offers an online IDE that can do the same as WebStorm and Truffle. To see this work, go to the Remix site: Paste in the “Hello, World” smart contract code from your example. Ensure that the right-side panel is set to the correct compiler; you will be using “Current version:0.4.22.” Then click “Start to compile (Ctrl-S).” See Figure 5-11. 193 Chapter 5 Ethereum Wallets and Smart Contracts Figure 5-11.  “Hello, World” smart contract Create a new folder in your project and name it remix; then create a file and name it HelloWorldContract.js. Click the Details button in Remix Online IDE and copy and paste the WEB3DEPLOY content into the HelloWorldRemix.js file you created, as shown in Figure 5-12. Figure 5-12.  “Hello, World” smart contract WEB3DEPLOY code 194 Chapter 5 Ethereum Wallets and Smart Contracts Note  web3.js is Ethereum JavaScript API; its libraries allow you to interact with an Ethereum node via an HTTP or IPC connection. The WEB3DEPLOY code can be deployed on a local or remote node. Private Ethereum Blockchain with Geth You have interacted with your smart contract on your local machine. Next, it’s advisable to run a full node and test your smart contract on a testnet blockchain; this tests it in a more realistic environment. Geth offers a full Ethereum node implemented in Go that you can run locally. This private testnet will allow you to develop and test your current smart contract in isolation from the real Ethereum blockchain. To get started, first install Geth using Brew. > brew tap ethereum/ethereum > brew install ethereum To ensure installation went well, run the -version command for the current Geth version (I am using 1.8.27 at the time of writing). > geth version Version: 1.8.27-stable Initialized Geth Private Blockchain Now that you have Geth installed, you will create your first block, or block 0, which is called the genesis block. Create a file called genesis_block.json and place it in the project root. For now just paste the provided JSON, but note that you can generate a custom genesis block with the Python script found here:­steps/. 195 Chapter 5 Ethereum Wallets and Smart Contracts For the scope of this book, you will use this script and set a low difficulty of 1000 and gas limit of 1000000 for easy mining and low gas fees; however, feel free to adjust as needed in your own experiments. See genesis_block.json. { “config”: { “chainId”: 1, “homesteadBlock”: 0, “eip155Block”: 0, “eip158Block”: 0 }, “difficulty”: “0x1000”, “gasLimit”: “0x1000000”, “alloc”: { “0x44dc998cbc1c7504bec0a96af4a9aef6606a768a”: {“balance”: “0x1337000000000000000000”} } } Next you will create your private testnet. In Terminal, run this command: > geth -identity “MyTestNet” -nodiscover -networkid 1999 -datadir testnet-blockchain init genesis_block.json You will need an account for your testnet-blockchain; use the account command. Select a simple password as you are running a local test network, but on mainnet you need to be mindful of security; here I’m choosing password 123. > geth account new -datadir testnet-blockchain Passphrase: 123 Repeat passphrase: 123 Address: { a8eceb3e2dd7af9c6fdb12edd8a7e84290932c2d} 196 Chapter 5 Ethereum Wallets and Smart Contracts As you can see, you received a wallet address after picking a password. You can compare your output with mine, as shown in Figure 5-13. Figure 5-13.  Creating a private testnet and wallet with Geth G eth Console Now that you have your account set and testnet-blockchain chain, you can open a Geth console to interact with the chain. > geth -identity “MyTestNet” -datadir testnet-blockchain -nodiscover -networkid 1999 console 2>> geth.log Notice that I used the 2>> geth.log param to output the logs into a custom file location. Once the Geth console starts, you can run the eth. syncing command to check the current block being synced. In this case, it will return false because there is nothing to sync; you are starting from block 0 on a local network. 197 Chapter 5 Ethereum Wallets and Smart Contracts You will receive a pop-up alert asking you the following: “Do you want the application “geth” to accept incoming network connections? Clicking Deny may limit the application’s behaviour. This setting can be changed in the Firewall pane of Security & Privacy preferences.” Select “Allow”. Next, in the Geth terminal, run the syncing command. geth> eth.syncing false If you run the eth.blockNumber command, it will return a zero as you have not mined any blocks yet. geth> eth.blockNumber 0 Mine Ethereum for Your Private Testnet You can then confirm you have a balance in your account with the getBalance command. geth> eth.getBalance(eth.accounts[0]) 0 With the eth.accounts command, you will get the new account you created. geth> eth.accounts [“0xa2a6d8fe7e39645613e74fe19c79071ee52009ba”] You can either generate or mine ether coins on the private Ethereum chain you created. Regardless, you need to know how to mine coins, because you will need transactions to be included in mined blocks as you test your code. To start mining, just run the miner.start command. 198 Chapter 5 Ethereum Wallets and Smart Contracts geth> miner.start() null Similarly, to stop mining, simply run the miner.stop command. > miner.stop() null If you let the mining run, you will mine some blocks, so when you check the block number, you will now see results as well as funds. geth> eth.blockNumber 1672 geth> eth.getBalance(eth.accounts[0]) 8.36e+21 Deploy Remix to Geth Now that your node is synced and you know how to mine, you can deploy your contracts to the testnet. First, you need to unlock your main Geth account to be able to use it. Ensure your account holds a balance; otherwise, you won’t be able to deploy your contract on the network. On Geth, unlock your account with your password so Geth can use it. geth> personal.unlockAccount(eth.accounts[0], “123”, 24∗3600) true I used the password 123, but you need to change it to your password if you used a different password. Next, load the web3.js script you generated on Remix. > loadScript(“remix/HelloWorldContract.js”) null [object Object] true 199 Chapter 5 Ethereum Wallets and Smart Contracts It takes a few seconds to mine the next block and include this contract; once it’s mined, you will receive the following message: Contract mined! address: 0x9905f1663f1b808d52dca42ce26e0d264 8f8be07 transactionHash: 0x66b80787eb3eae16c9535a1bd86ff1a 623c1914ac9ffc2addde74655aed09157 If you are not seeing this message, make sure you are mining. geth> miner.start() Once the contact is mined, you will get the following message in Terminal, which includes the address and transaction hash: Contract mined! address: 0xe49da16551c5c5735de46e07e8ab9e 713310a13b transactionHash: 0x36d3ec593f63280ca6aae1b079bfb6 f00eea719468e04960643c23f39cbef5b3 Deploy Truffle to Geth Similarly, to deploy the web3.js contract’s script via Truffle, you run the migrate -reset command. The -reset flag tells Truffle to run all the migrations from the beginning. Ensure you use .exit to exit the Truffle console prior to running the migrate command. Truffle will compile your contract automatically. truffle(development)> .exit > truffle migrate -reset Using network ‘development’. Network up to date. 200 Chapter 5 Ethereum Wallets and Smart Contracts Now you can open a development console again. > truffle console -network development truffle(development)> HelloWorldContract.deployed().then(_app => { hello = _app }) undefined truffle(development)> hello.greet() ‘Hello World’ The contract is redeployed, and you can interact with your contract again. You can download this step from here: Apress/the-blockchain-developer/chapter5/step2/. Useful Commands in Geth You can stop the Geth process by pressing Command+C and then exit, or you can stop the process via aux to check whether there are any processes open. Or you can use the killall command to stop the process. > ps aux | grep geth > killall -HUP geth At any time, you can run the help flag to get a list of commands. > geth -help To get a list of the pending transactions, run the following: > geth -identity “MyTestNet” -datadir testnet-blockchain -nodiscover -networkid 1999 console 2>> geth.log geth> eth.pendingTransactions To remove your locally synced blockchain data from the public testnet, use this: geth> geth removedb 201 Chapter 5 Ethereum Wallets and Smart Contracts To remove your private blockchain testnet data, use this: geth> geth removedb -datadir test-net-blockchain To synchronize the blockchain more quickly, use the  -fast flag to perform a fast Ethereum sync. Note that you will not retain the past transaction data with this command. The cache flag sets the cache limit. geth> geth -fast -cache=1024 onnect the Mist Ethereum Wallet to Your C Private Network It would be useful to have a wallet to connect to your private network. That’s where Mist is helpful. You can connect your private blockchain to Mist and perform transactions, conducting realistic transactions as if people were using your contracts. To get started, download Mist from here: ethereum/mist/releases. For Mac, the file to download is called Mist-macosx-0-11-1.dmg at the time of writing. Note that you can also achieve the same results with an Ethereum wallet, which you can download from the same URL. Next, you will be starting Mist and connecting it to your testnet blockchain. At the command line, point to Mist’s location and the geth. ipc database. > /Applications/ -rpc /[project location]/MySmartContract/testnet-blockchain/geth.ipc 202 Chapter 5 Ethereum Wallets and Smart Contracts Mist opens and shows your active account and balance, as shown in Figure 5-14. Figure 5-14.  Mist active account and balance Others to Interact with Your Smart Contract Once the contract is published, anyone can use the address and application binary interface (ABI) to connect and interact with the contract. You can start and interact with your contract as if an actual person is using your contract prior to publishing it to mainnet. Mist is a desktop app that can be used for testing. To watch a contract, in Mist, click the Contracts link at the top right and then click Watch Contract, as shown in Figure 5-15. 203 Chapter 5 Ethereum Wallets and Smart Contracts Figure 5-15.  Mist’s Watch Contract button For others to run your contract, they need two things. • Contract address • Application binary interface Note An ABI describes the contract’s functions. This description is needed in order to know how to call the function. Think of it as a user manual. You can retrieve the contract address, as shown here: truffle(development)>var hello = HelloWorldContract.deployed(). then(_app => { hello = _app }) truffle(development)>hello.address ‘0x0b4f69f88390bc8cec93e730128a5e5c5dffd56c’ Similarly, you can retrieve the contract’s ABI with this command: truffle(development)>JSON.stringify(hello.abi) ‘[{“inputs”:[],”payable”:false,”stateMutability”:”nonpayable”,” type”:”constructor”,”signature” ‘[{“inputs”:[],”payable”:false, “stateMutability”:”nonpayable”,”type”: “constructor”,”signature”:”constructor”},{“constant”:true, “inputs”:[],”name”:”greet”,”outputs”:[{“name”:””,”type”:”string”}], “payable”:false,”stateMutability”:”view”,”type”:”function”, “signature”:”0xcfae3217″}]’ 204 Chapter 5 Ethereum Wallets and Smart Contracts Then pass the contract address and ABI in Mist, as shown in Figure 5-­16. Figure 5-16.  Passing info in Mist Notice that you omit the single quote from the ABI and address before pasting it into Mist. Now click OK, and you can see your contract in the watched contracts list. See Figure 5-17. 205 Chapter 5 Ethereum Wallets and Smart Contracts Figure 5-17.  Mist’s watched contracts You have your contract in Mist, and you can interact with it, send funds, listen to events, and interact with functions, just as users will interact with your contract on mainnet. M etaMask Similar to Mist, another way to interact with your contracts, without even downloading a desktop app, is in your Chrome or Firefox browser with a plugin called MetaMask. Just as with Mist, you can utilize MetaMask to connect your contract to mainnet, a public testnet, and a local blockchain (such as the one you created with Ganache), or you can even connect to Truffle Develop. To get started, download the MetaMask plugin for Chrome or Firefox. 206 • Chrome Web Store: https://chrome. nkbihfbeogaeaoehlefnkodbefgpgknn. Click the Add to Chrome button. See Figure 5-18. • Firefox Add-ons page: en-US/firefox/addon/ether-metamask. Click the Add to Firefox button. Chapter 5 Ethereum Wallets and Smart Contracts Figure 5-18.  MetaMask beta Chrome add-on Click the MetaMask icon and then the Continue button. Next, select a password, accept the terms, save your secret backup phrase, and create your account. Now that the account is created, you have an option in the top drop-­down of which network to connect to, as shown in Figure 5-19. 207 Chapter 5 Ethereum Wallets and Smart Contracts Figure 5-19.  MetaMask beta Chrome network drop-down As you might recall, you programmed the truffle.js values to set a network on localhost port 8584, which matches the default network; however, you can set a custom RPC or connect to testnet or mainnet. For more information regarding connecting Truffle with Metamask, visit the Truffle framework docs; truffle-with-metamask 208 Chapter 5 Ethereum Wallets and Smart Contracts Public Testnet Now that you are able to run your smart contract on a development network, you can take an additional step prior to going to mainnet. You can run your contract on a public testnet network. Syncing Blocks There are three well-known testnets: Ropsten, Kovan, and Rinkeby. You can program Geth to connect to a testnet with the -testnet flag, which will connect to the public testnet network (Ropsten). > geth -testnet -syncmode “fast” -cache=512 console As before, the rpc flag is needed to accept the Geth RPC connections and for Truffle to be able to connect to Geth. You are also setting it to fast sync and limiting the cache size to 512. This command includes starting the Geth console. To check the status of the syncing command, use this: geth> eth.syncing { currentBlock: 1011878, highestBlock: 3569550, knownStates: 2058862, pulledStates: 2056745, startingBlock: 968873 } Once complete, the syncing command will return false. Keep in mind that there are millions of state entries and 3,569,550 blocks at the time of writing, which could take hours depending on your connection speed. The currentBlock value is the current block being retrieved out of a total 209 Chapter 5 Ethereum Wallets and Smart Contracts ­ umber of blocks (the highest block). This can give you an idea of how n long the download will take. As you recall, you can check current block number being sync by running the eth.blockNumber command in a Geth console, as well as check your balance in your account to see whether it has been updated yet. > eth.blockNumber > eth.getBalance(eth.accounts[0]) Public Testnet Faucet In addition to the testnet coins, you can get additional testnet coins via a faucet, just as you did with bitcoin. Go to, as shown in Figure 5-20, and request coins to your wallet address set in Mist. Figure 5-20.  Ropsten Ethereum faucet 210 Chapter 5 Ethereum Wallets and Smart Contracts Ethereum Mainnet From the Ganache console, you were able to publish to a public testnet network (Ropsten). The next step is to publish to the Ethereum mainnet. To do so, you will restart Geth and connect this time to the mainnet. > geth -fast -cache=512 Just as with the public testnet, you will have to wait for Geth to sync. Once syncing is complete, you can call the Truffle migrate command to deploy, and as before, you need your account to have ether coins. > truffle migrate -reset Recommended Tools for Smart Contracts In this chapter, I covered Ganache, Solidity, IntelliJ, Truffle, Geth, Remix, and MetaMask; however, there are other tools worth mentioning. – Solium: Solidity code cleaning solution – Interacting with smart contracts – Populus: Development framework for Ethereum smart contracts – Parity: Light-weight Ethereum node – Drizzle: Front-end dapp solution Summary In this chapter, I covered how to utilize Ganache to simulate a full-node Ethereum client. You installed Ganache, and once you were able to connect to the Ganache CLI, you were able to create a network and listen to a port. You learned how to use the IntelliJ IDEA plugin for Solidity to 211 Chapter 5 Ethereum Wallets and Smart Contracts easily develop smart contracts with autocomplete and highlights. You also learned about the Truffle Suite and how to create your own smart contracts using the command-line wizard. You connected Truffle to the Ganache network and then created a “Hello, World” smart contract as well as “MD5SmartContract” smart contract. Once you created your contracts, you were able to migrate your smart contract utilizing the Truffle deployment process. You compiled and deployed your smart contract code with Truffle to your development network. Then, you used the Truffle console to interact with your smart contract via the Truffle CLI. Next, you created a private Ethereum blockchain with Geth and initialized the blockchain. You utilize the Geth console and mined pretend Ethereum on your Geth private testnet. Next, you deployed your Remix web3.js to the Geth private testnet you created, as well as deployed your Truffle contracts. In addition, you looked at some useful Geth commands that will help you while developing smart contracts. You connected your Mist Ethereum wallet to the private Geth network you created and were able to interact with your smart contract. You were able to use MetaMask in your browser as a replacement for a desktop client. Once you were able to see your contract working, you set a public testnet and synced blocks as well as got coins via a faucet. Lastly, you learned how to migrate your code to the Ethereum mainnet. In next chapters, you will learn how to build front-end code for smart contracts and publish a complete dapp. 212 EOS.IO Wallets and Smart Contracts In Chapter 2, I introduced EOS.IO when I covered bitcoin, altcoins, and different consensus mechanisms. Specifically, I covered how EOS.IO is an example of altcoins that turn into tokens; you created an EOS block producer and were able to create a full node capable of mining EOS tokens. Ethereum was the beginning of your blockchain smart contract development, and you learned to use the Solidity language to write smart contracts and dapps. EOS.IO has created a more robust architecture than Ethereum for smart contract and dapp development. In this chapter, I will expand on the EOS.IO blockchain and show how to build a EOS.IO smart contract that can be used in decentralized applications (dapps). You will set up a local testnet environment and learn how to configure the EOS.IO tools and libraries. You will learn about EOS.IO wallets and how to create, delete, and back up wallets as well as perform operations such as opening, locking, and unlocking a wallet. I will cover the wallet’s key pairs and how to spin up and re-spin up a local testnet block producer. You will learn about permissions and single-signature and multisignature options. To better understand EOS.IO smart contracts, you will create a “HelloWorld” smart contract and smart contract token. You will create accounts, write smart contract C++ code, compile code, and generate WebAssembly and ABI files as well as Ricardian contracts. You then will learn how to deploy your smart contracts and interact with them, as well as issue tokens and transfer tokens to another user. Chapter 6 EOS.IO Wallets and Smart Contracts Lastly, you will connect to a public testnet block producer for testing in a more realistic environment as well as connecting and publishing on a mainnet block producer. Note  EOS is the native cryptocurrency (token) that powers the EOS.IO software. EOS.IO is an industrial-scale, fully customized blockchain architecture protocol that enables decentralized applications by providing access to the parts that make up the blockchain. Think of EOS.IO as a blockchain OS as it emulates a real computer and enables access to resources such as the CPU, GPU, RAM, and hard disk. EOS.IS does not charge transaction fees while performing millions of transactions per second. An EOS token is a utility token, and owning the token (staking) provides bandwidth and storage on the EOS.IO blockchain. You receive resources in proportion to the total stake you own to the total stake (owning 1 percent of EOS tokens gives usage up to 1 percent of total EOS.IO bandwidth). “EOS.IO software introduces a new blockchain architecture designed to enable vertical and horizontal scaling of decentralized applications. This is achieved by creating an operating system-like construct upon which applications can be built. The software provides accounts, authentication, databases, asynchronous communication, and the scheduling of applications across many of CPU cores or clusters. The resulting technology is a blockchain architecture that may ultimately scale to millions of transactions per second, eliminates user fees, and allows for quick and easy deployment and maintenance of decentralized applications, in the context of a governed blockchain.” —EOS.IO white paper 214 Chapter 6 EOS.IO Wallets and Smart Contracts As mentioned in Chapter 2, EOS.IO is built on the delegated proof of stake (DPoS) consensus. EOS.IO is able to handle low latency and tens of millions of active users daily (bypassing Ethereum). This is achieved by the DPoS consensus as well as EOS.IO running as multithreaded (running on multiple computer cores) and acting as an OS. This type of scalability can enable adoption of blockchain technology by large businesses. EOS.IO offers many additional features such as the following: • Free rate-limited transactions • Low-latency transactions (such as 0.25 seconds broadcast time or 0.5 block time) • Recovery of stolen keys • Parallel execution of applications • Atomic transactions with multiple accounts I encourage you to read the EOS.IO white paper and visit the GitHub page for a full list of features. – – Financially speaking, EOS was developed by a private company called and was able to raise an astonishing $4 billion in initial coin offering (ICO) via an ERC-20 tokens sale. At the time of writing, EOS’s price is selling around $2 to $8, and it has a total market capitalization of around $2 billion, which makes EOS the seventh largest cryptocurrency by market cap. EOS offers a few repositories to help with the development of EOS.IO contracts; they are listed at and include the following: eos, eosio.cdt, eosjs, demux-js, and eosio.contracts. You will be installing the EOS and EOSIO.CDT libraries in this chapter. The EOS library is an open source smart contract platform, and the EOSIO.CDT library is a suite of tools for building EOS.IO contracts. 215 Chapter 6 EOS.IO Wallets and Smart Contracts At the time of writing, the EOS.IO platform has a steep learning curve. The code keeps changing, and the documentation and examples of EOS.IO are not being updated in timely manner, so it may feel like chasing a moving target at times. This results in code sometimes not compiling, commands not working, and documentation and examples containing code and commands that have been deprecated. It’s easy to find yourself stumped a few times while developing a contract; however, once you understand EOS.IO, it’s easy to overcome these obstacles. Setting Up a Testnet Environment Before jumping into coding, let’s start by installing EOS.IO and EOSIO. CDT. You will build your EOS.IO version and set up a local testnet block producer. Then you will learn about the EOS.IO tools called cleos, keosd, and nodeos and how to configure them and create and manage a wallet with cleos. These tools and libraries are necessary for development. I nstall EOS.IO The easiest way to install EOS.IO on macOS is with Brew. > brew tap eosio/eosio > brew install eosio The current EOS.IO is version 1.7.3. I recommend checking the repo and issues section on GitHub ( or doing a Google search in case you encounter errors when installing or building EOS.IO. Also see Once the installation is complete, you will see the message in Figure 6-­1 in Terminal. 216 Chapter 6 EOS.IO Wallets and Smart Contracts Figure 6-1.  EOS.IO successfully built Next, add the EOS.IO binaries location to your environment, so you can run nodeos from anywhere. > export PATH=$PATH:/usr/local/eosio/bin This will set the path variable on this Terminal session, but you want to set the path environment variable permanently, so add it to your bash_ profile file by opening the file with vim or your favorite text editor. > vim ~/.bash_profile Next, insert the following lines: # Setting PATH for EOSIO PATH=”/usr/local/eosio/bin:${PATH}” Lastly, run bash_profile to commit the changes. > . ~/.bash_profile EOS.IO comes out of the box with built-in tools and programs; they are here: /usr/local/eosio/. Figure 6-2 shows an architecture diagram of these tools. • nodeos: This is the core EOS.IO daemon that enables you to run a blockchain node component. nodeos can be configured with plugins. Additionally, nodeos can be configured to run a block producer in a local development environment or on dedicated endpoints. It interacts with a blockchain by creating blocks. 217 Chapter 6 • EOS.IO Wallets and Smart Contracts cleos: This is the main command-line tool for EOS.IO. It interfaces with the REST API exposed by nodeos. It can also access wallets as it interacts with keosd. For a list of cleos commands, just run the following: > cleos • keosd: This is the wallet daemon to load and manage the wallet’s keys. It does this by loading wallet-related plugins, such as the HTTP interface and the RPC API. • eosio-launcher: This tool will help you deploy a multinode blockchain network. Figure 6-2.  Basic architecture of EOS. Photo credit: Install EOSIO.CDT You installed EOS.IO. The other important library you need is EOSIO.CDT (CDT stands for “contract development toolkit”). EOSIO.CDT is the suite of tools used to build EOS.IO contracts. To get the library installed, you will be using Brew. 218 Chapter 6 EOS.IO Wallets and Smart Contracts > brew tap eosio/eosio.cdt > brew install eosio.cdt The latest EOSIO.CDT at the time of writing is version 1.6.1. Run brew update if you have an older version. > brew upgrade eosio.cdt To ensure installation went well, run the eosio-cpp command with the help argument. > eosio-cpp -help As you recall, you used Truffle and Remix to generate the Ethereum’s application binary interface (ABI) files. For EOS.IO smart contracts, you use eosio-cpp, which is a compiler that generates a WebAssembly (.wasm) file, which is the ABI that is needed to be uploaded to the blockchain for the smart contract. eosio-cpp also generates helper functions that serialize/deserialize the types defined in the ABI code for the smart contract development. You can find more information about EOSIO.CDT on the GitHub page: In the future, if you need to remove EOSIO and EOSIO.CDT, run the following commands: > brew remove eosio > brew remove eosio.cdt Note  eosio-cpp is the replacement for eosiocpp, which has been deprecated. Originally eosiocpp was part of the EOS.IO installation, but now it’s part of CDT. 219 Chapter 6 EOS.IO Wallets and Smart Contracts B uild EOS.IO A good way to visually understand EOS.IO and the tools associated with EOS.IO is to look at Figure 6-2. keosd and nodeos Configuration Files The default ports for keosd and nodeos utilize the same port: 8888. To configure nodeos, see this config file: > vim “/Users/[user]/Library/Application Support/eosio/nodeos/ config/config.ini” Inside the config.ini file, a notable variable to change is the plugins list that you load. You won’t make changes, but as you advance in your development, you may need to make changes. Like with nodeos, you can configure keosd by editing this config file: > vim ~/eosio-wallet/config.ini Once you open the file, note that there is a variable named httpserver-address that can be used to change from port 8888 in case you need that port for other software. Here let’s set it to any port you like. The variable is commented out. To set it to port 9000, change it from this: # http-server-address = to the following: http-server-address = You could use the default port; however, it’s good to know how to configure EOS.IO. 220 Chapter 6 EOS.IO Wallets and Smart Contracts Create and Manage a Wallet with cleos In the previous section, I introduced some EOS.IO built-in programs and tools. As mentioned, cleos provides a REST API interface that is exposed by nodeos. The cleos reference guide can be found here: https:// To find the cleos -version number, run the -version client command. At the time of writing, you get to build d4ffb4eb. > cleos version client d4ffb4eb As mentioned, to get a list of commands, just type cleos. or cleos -help;. > cleos -help If you don’t remember a specific subcommand, type the command and get the subcommands list in the output; for instance, the get command outputs the subcommands list such as info for your block producer’s info. > cleos get > cleos get info Failed to connect to nodeos at; is nodeos running? Notice that as you don’t have a node running, you get no results and an error message; however, later in this chapter, when you spin up nodeos, you will get information about your block producer. 221 Chapter 6 EOS.IO Wallets and Smart Contracts EOS.IO Wallets The EOS.IO wallets use keys and offer a locked (encrypted) state and an unlocked (decrypted) state to protect the keys. The lock and unlock commands need the high entropy password that is provided to you once you create a wallet. The wallet’s keys can be associated with an account to provide permission to the account’s tokens, but it’s not necessary for the creation of a wallet. The wallet’s software uses cleos as the intermediary layer between keosd key retrieval operations and the nodeos blockchain actions. For instance, you can use cleos to access an account as it requires signatures to be generated from the keys. To create the default wallet, just run the create wallet command. Use the -to-console flag to get the master key (password). > cleos wallet create -to-console Creating wallet: default Save password to use in the future to unlock this wallet. Without password imported keys will not be retrievable. “[ DEFAULT_MASTER_KEY]” Make sure you store the password. Now you can check that the wallet was created and run the wallet list command, and you will be able to see an array that lists the wallets and includes the default wallet you created. > cleos wallet list Wallets: [ “default ∗” ] 222 Chapter 6 EOS.IO Wallets and Smart Contracts Notice that once you create your default wallet, there is an asterisk next to the wallet’s name. The asterisk means that it’s unlocked. You’ll learn more about the lock and unlock states in the next section. Delete and Back Up Wallets To remove the wallet you created, you need to remove the actual wallet’s file; it’s located here: ~/eosio-wallet. > rm -rf ~/eosio-wallet Run the wallet list command, and you can see that the wallet array is empty. > cleos wallet list “/usr/local/eosio/bin/keosd” launched Wallets: [] To back up the wallet, copy the wallet’s files and store them in a safe location. EOS.IO Wallet with Custom Name So far, you created the default wallet. Now let’s say you want to create another wallet and name it mywallet. All you have to do is utilize the -n or -name flag. Choose a name and be careful about the strict name restrictions (a-z and 1-5 are allowed only, with a length of 12). I am choosing mywallet. > cleos wallet create -n mywallet -to-console Creating wallet: mywallet Save password to use in the future to unlock this wallet. Without password imported keys will not be retrievable. “[DEFAULT_MASTER_KEY]” 223 Chapter 6 EOS.IO Wallets and Smart Contracts EOS.IO: Open, Lock, and Unlock a Wallet When you created your wallet, you got a high entropy master key, which is your password. This password is used to encrypt (lock) and decrypt (unlock) your wallet file. To lock and unlock your wallet, use the following commands: > cleos wallet lock -n mywallet > cleos wallet unlock -n mywallet password: [DEFAULT_MASTER_KEY] password: Unlocked: mywallet The lock and unlock commands enable your wallet to set a state of encryption and decryption that is protected by your password. What you are protecting are the wallet’s keys. To unlock the default wallet, just run the following: > cleos wallet unlock Also, to perform operations on your wallets, you need to first open the wallet. When keosd gets restarted, the wallet will be closed. Run the open command to open the wallet as needed. > cleos wallet open Opened: default Generating EOS.IO Keys Just as in other blockchains, EOS.IO stores keys in a wallet. You generate these keys and assign them to an EOS.IO account. There are multiple ways to create keys. You will be using cleos here. First let’s re-create the default wallet, in case you deleted it previously. > cleos wallet create -to-console Creating wallet: default 224 Chapter 6 EOS.IO Wallets and Smart Contracts Save password to use in the future to unlock this wallet. Without password imported keys will not be retrievable. “[DEFAULT_MASTER_KEY]” Running wallet list should show you two wallets. > cleos wallet list Wallets: [ “default”, “mywallet ∗” ] Next, to create two public/private key pairs, run the create key command. > cleos create key -to-console Private key: [PRIVATE_KEY_1] Public key: [PUBLIC_KEY_1] > cleos create key -to-console Private key: [PRIVATE_KEY_2] Public key: [PUBLIC_KEY_2] As you noticed, you ran the create key command twice. This is not a typo; you need to have two keys: one for the active user and one for the owner. You’ll learn more about this concept once you create an account. The command you ran output key pairs of public and private keys. Notice that the public key starts with the EOS keyword. These arbitrary key pairs are meaningless by themselves because they have no authority (they do not belong to any wallet or account). To assign these key pairs to a wallet, you can import these keys into your wallet. > cleos wallet import -private-key [PRIVATE_KEY_1] imported private key for: [PRIVATE_KEY_1] 225 Chapter 6 EOS.IO Wallets and Smart Contracts imported private key for: [key] > cleos wallet import -private-key [PRIVATE_KEY_2] imported private key for: [PRIVATE_KEY_2] In the output of your command, you received a confirmation message from the command line that the key pairs were added. However, you can also confirm that the key pairs were added by calling the wallet keys command. > cleos wallet keys [PUBLIC_KEY_1, PUBLIC_KEY_2] Additionally, you can request to view the key pairs. > cleos wallet private_keys -password [DEFAULT_MASTER_KEY] [[PUBLIC_KEY_1, PRIVATE_KEY_2],[ PUBLIC_KEY_1, PUBLIC_KEY_2]] In the previous command, you passed the -password argument instead of waiting for the command line to ask that you enter your master password. Lastly, you need to import a special EOS.IO parent account. This special parent account is used to bootstrap the EOS.IO nodes. Without this private key, you won’t be able to create your account. EOS.IO accounts need a parent account to create another account; that’s how EOS.IO allocates resources and protects against spam and hackers. > cleos wallet import -private-key 5KQwrPbwdL6PhXujxW37FSSQZ1JiwsST4cqQzDeyXtP79zkvFD3 imported private key for: EOS6MRyAjQq8ud7hVNYcfnVPJqcVpscN5So8BhtHuGYqET5GDW5CV Note  At the time of writing, the parent wallet works; however, this can change, and you may need to find a parent wallet that can be used to bootstrap the EOS.IO wallet. 226 Chapter 6 EOS.IO Wallets and Smart Contracts Take a look at your output in case you would like to compare yours with mine; see Figure 6-3. Figure 6-3.  Setting up EOS.IO wallet keys with a special parent account Spin Up a node with nodeos Transactions are attached to a block, and you need a block producer to be able to pass these transactions to the network. You can skip creating an EOS node (nodeos) if you connect directly to a public testnet or the mainnet; however, it’s better to first run your smart contracts on a local testnet network before committing your code to a public testnet or mainnet. At this point, you should be used to this process as you did the same thing when you developed a smart contract for Ethereum. Feel free to revisit Figure 6-2, where you can see the diagram of nodeos and the EOS. IO blockchain relationship. To start your own single-node local blockchain block producer, in a separate terminal, run nodeos. > nodeos -e -p eosio -plugin eosio::chain_api_plugin -plugin eosio::history_api_plugin -contracts-console 227 Chapter 6 EOS.IO Wallets and Smart Contracts This command starts the block producer and should display the process on the console. info 2019-04-28T19:03:34.776 thread-0 chain_plugin.cpp:333 plugin_initialize ] initializing chain plugin info 2019-04-28T19:03:34.811 thread-0 block_log.cpp:134 open ] Log is nonempty info 2019-04-28T19:03:34.820 thread-0 block_log.cpp:161 open ] Index is nonempty info 2019-04-28T19:03:34.878 thread-0 http_plugin.cpp:422 plugin_initialize ] configured http to listen on … … … As you can see, the console shows that your local network starts producing blocks. Notice the command you used sets the plugins, and also you set the -contracts-console flag. This flag is necessary to be able to see messages you print to the console while in development mode. Note  You can also set the -contracts-console flag inside the config.ini file instead of passing this argument with nodeos every time. As you recall, you previously were running the cleos get info command and getting no results, as you did not have a block producer running; now if you run the same command in a new Terminal, you can observe information about your blocks. 228 Chapter 6 EOS.IO Wallets and Smart Contracts > cleos get info { “server_version”: “d4ffb4eb”, “chain_id”: “cf057bbfb72640471fd910bcb67639c22df9f92470936cd dc1ade0e2f2e7dc4f”, “head_block_num”: 73699, “last_irreversible_block_num”: 73698, “last_irreversible_block_id”: “00011fe2a80bf11315396c85e70860 122dddc24ac083911fba31f7ee2d64eb3e”, “head_block_id”: “00011fe36fab1fc2d4885067e1391c72782895d43f14 cf7970ac282ddef17d67”, “head_block_time”: “2019-04-28T19:04:06.500”, “head_block_producer”: “eosio”, “virtual_block_cpu_limit”: 200000000, “virtual_block_net_limit”: 1048576000, “block_cpu_limit”: 199900, “block_net_limit”: 1048576, “server_version_string”: “v1.5.1-dirty” } Re-spin Up a Testnet Local node (nodeos) If you want to clear the block producer’s history, delete all the blocks, and re-spin up your local testnet, you will use what is called a hard replay by using the following flags: -delete-all-blocks -delete-state-history -hard-replay These arguments will clear the accounts on the local testnet as well as the blocks. The complete command will look as follows: > nodeos -e -p eosio -plugin eosio::chain_api_plugin -plugin eosio::history_api_plugin -delete-all-blocks -delete-statehistory -hard-replay -contracts-­console 229 Chapter 6 EOS.IO Wallets and Smart Contracts E OS.IO Accounts EOS.IO accounts hold a human-readable name that is stored on the EOS. IO blockchain. To create an account on the mainnet, someone with an EOS.IO account needs to create it for you. The reasons behind this regulated process are spam and hacker prevention and resource allocation. By default, the account holds two native names/permissions. – Owner: This is used to recover other permissions, which is useful in the event that the permission has been compromised. – Active: This is used for high-level account changes such as transferring funds or voting for block producers. When you created your testnet account, you imported a special EOS.IO parent account key to bootstrap. Each permission name needs a “parent.” The parent authority is to be able to make changes to any of the permission settings for all of its children. EOS.IO provides a special account’s parent key for the local testnet that you imported in order to create your account. See Figure 6-4. 230 Chapter 6 EOS.IO Wallets and Smart Contracts Figure 6-4.  Account high-level architecture and permission structure. Photo credit: For a transaction to be valid and signed, each named permission needs conditions to be met such as a client with an unlocked wallet, and the wallet has to grant authority permission for the account. If you don’t meet these conditions, the transaction will fail. Now that you understand accounts, you are ready to create your own account. You already created a wallet and imported the parent key. To create an account, you run the following command’s syntax: > cleos create account eosio [ACCOUNT_NAME] [OWNER_PUBLIC_KEY] [ACTIVE_PUBLIC_KEY] The OWNER_KEY value is the public key of the account owner authority, and the ACTIVE_KEY value is the public key of the account’s active authority. 231 Chapter 6 EOS.IO Wallets and Smart Contracts In this example, let’s call the account myaccount and use the two keys you created. The command will look like so (see Figure 6-5 for the expected output): > cleos create account eosio myaccount [PUBLIC_KEY_1] [PUBLIC_KEY_2] Figure 6-5.  Creating your first EOS.IO account called myaccount You generated two keys, so it doesn’t matter which key you decide to use as your active and which one as an owner; just remember which key you used for which. To see the list of the account, use this: > cleos get accounts [PUBLIC_KEY_1] { “account_names”: [ “myaccount” ] } Note  You may get an error message while trying to create the account if you missed any of the steps provided in this chapter. The error is “Error 3090003: provided keys, permissions, and delays do not satisfy declared authorizations.” 232 Chapter 6 EOS.IO Wallets and Smart Contracts allets, Keys, and Accounts: Complete W Commands To ensure you fully understand the process, here is a summary of how to create an account: 1. Ensure nodeos is running in a separate Terminal window. > nodeos -e -p eosio -plugin eosio::chain_api_plugin -plugin eosio::history_api_plugin -delete-all-blocks -delete-state-history -hard-replay -contracts-­ console 2. Ensure your wallet is unlocked. Run > cleos wallet list (check that there is an asterisk next to the wallet’s name). 3. The EOS.IO special account’s parent key (5KQwrPbwd L6PhXujxW37FSSQZ1JiwsST4cqQzDeyXtP79zkvFD3) was imported to bootstrap the EOS.IO. cleos wallet import -private-key 5KQwrPbwdL 6PhXujxW37FSSQZ1JiwsST4cqQzDeyXtP79zkvFD3 4. Check the key’s list using > cleos wallet keys. It should output an array with the keys you imported. To summarize what you have done so far or to redo the entire process of creating an account, here are the complete steps: > > > > > > > rm -rf ~/eosio-wallet cleos wallet create -to-console cleos wallet open cleos wallet unlock -password [DEFAULT_MASTER_KEY] cleos create key -to-console cleos create key -to-console cleos wallet import -private-key [PRIVATE_KEY_1] 233 Chapter 6 EOS.IO Wallets and Smart Contracts > cleos wallet import -private-key [PRIVATE_KEY_2] > cleos wallet import -private-key 5KQwrPbwdL6PhXujxW37FSSQZ1JiwsST4cqQzDeyXtP79zkvFD3 > cleos wallet keys > cleos create account eosio myaccount [EOS∗ OWNER_KEY] [EOS∗ ACTIVE_KEY] ustom, Single Signature (Single-Sig), C and Multisignature (Multisig) By default, you configured your account with a single signature (aka singlesig) because it’s authorized for actions with the default (active and owner) permissions. However, it’s possible to configure your accounts with a multisignature (aka multisig) or with custom permissions. For instance, you can configure your account with multiple keys to authorize specific owner actions and active actions. You could use this feature, for instance, to create a permission called “publish” and give this permission to an account to allow only published smart contracts without the ability to withdraw tokens. “HelloWorld” Smart Contract You will be writing a smart contract with the minimal code. You will call your smart contract “HelloWorld.” “HelloWorld” Smart Contract Accounts To get started, you will create two accounts for your smart contract, one to publish your smart contract and one for interacting with a user. See the output in Figure 6-6. > cleos create account eosio helloworld [PUBLIC_KEY] > cleos create account eosio john [PUBLIC_KEY] 234 Chapter 6 EOS.IO Wallets and Smart Contracts Figure 6-6.  Creating your accounts for the “HelloWorld” smart contract “HelloWorld” C++ Code EOS selected C++, which resulted in mixed reviews from the blockchain development community. C++ is a low-level language, and it allows better management of resources such as memory pointers and operator overloading. This can result in better performance; however, it comes with a cost of increased code effort, especially if you are not familiar with C++. The EOS.IO infrastructure is written in C++, so it should not be a surprise that C++ was selected by EOS.IO’s team. EOS.IO smart contracts are written in C++ saved as the CPP file format; then you compile the C++ code to WebAssembly that is then used for deployment. Note  EOS.IO smart contract source files can be broken into three: CPP, HPP, and Ricardian. The HPP file defines the smart contract class, actions, and tables. The CPP file is the C++ code, which implements the action logic. The Ricardian file is the digital document (more about this in the next section). Start by creating the helloworld contract directory by navigating into the directory. > mkdir ~/Desktop/helloworld && cd $_ Notice that you used your desktop but can use any directory you like. Next, paste the helloworld.cpp code with vim or your favorite text editor. 235 Chapter 6 EOS.IO Wallets and Smart Contracts > vim helloworld.cpp #include using namespace eosio; class helloworld : public contract { public: using contract::contract; [[eosio::action]] void hello( name user ) { print( “World: User: “, user); } }; EOSIO_DISPATCH(helloworld, (hello)) The code imports EOS.IO libraries. The class HelloWorld is of type contract, and you create a method called hello. The method is your action; you pass the user and print the word world and the username. Once a user interacts with your contract and calls the hello action, they will get world with the user’s name. Notice that in this example you included the eosio.hpp file. To debug the EOS.IO smart contract, you need to use old-fashioned caveman debugging. Note  Caveman debugging, aka printf() debugging, is nothing more than adding print statements around your code. The EOS.IO Print API supports the char array, 64-bit and 128-­bit unsigned integer, and others. The print is done by wrapping the C++ code printi, prints_l, printi128, and others in print.hpp, which includes the import eosio.hpp library statement. 236 Chapter 6 EOS.IO Wallets and Smart Contracts Smart Contract IDE Using Terminal is perfectly acceptable, but as the code becomes more complex, using a professional IDE can be helpful for code completion, highlights, and readability. You can use the IDE of your liking. As you already used WebStorm, you can continue and import the project to WebStorm. WebStorm already includes a C++ plugin, so there’s no need to install any special plugin. Figure 6-7 shows HelloWorld project open in WebStorm. To import your project, select File ➤ Open and navigate to the project’s location: ~/Desktop/helloworld. Figure 6-7.  HelloWorld project imported into WebStorm version 2018.2.4 237 Chapter 6 EOS.IO Wallets and Smart Contracts Compile a Contract and Generate an ABI As mentioned, the eosio-cpp tool takes C++ code and outputs WebAssembly and ABI. This is done by running the following command: > eosio-cpp -o helloworld.wasm helloworld.cpp -abigen Notice that in the command you specify the output file’s name, which is helloworld.wasm. After running this command, the compiler generates the following files: helloworld.wasm and helloworld.abi. To ensure the compiler worked as expected, you should be able to see these two files; see Figure 6-7. R icardian Contracts Once you generate your WASM and ABI files, notice that you are getting more than 20 warnings. Among these warnings, you should find the following warnings in the output: Warning, empty ricardian clause file Warning, empty ricardian clause file Warning, action does not have a ricardian contract Note  Ricardian contracts were invented by Ian Grigg in 1996 to help bridge the gap between software application and court of law. The Ricardian contracts file in EOS is a digital document in Markdown Language format (.md, .markdown) and defines the terms and conditions of the interaction between the parties. It is set as parameters but written as readable text. EOS uses cryptographically to sign and verify the Ricardian contracts. 238 Chapter 6 EOS.IO Wallets and Smart Contracts To help generate the Ricardian contracts, you can copy a Python script and template from a contributor that generates the files automatically: As it’s just three files, instead of using clone, you can use wget to download these files. Check that you have wget installed on your machine. > wget -help In case it’s not installed, install wget on macOS via Ruby and Brew. > ruby -e “$(curl -fsSL Homebrew/install/master/install)” < /dev/null 2> /dev/null > brew install wget > brew upgrade wget Next, inside your helloworld project, create the directory and download the files you need. > cd ~/desktop/helloworld > mkdir rc && cd $_ > wget governance/master/scripts/abi_to_rc/ > wget governance/master/scripts/abi_to_rc/ > wget governance/master/scripts/abi_to_rc/ Next, run the Python script. > cd ../ > python rc/ helloworld.abi 239 Chapter 6 EOS.IO Wallets and Smart Contracts The script generates for you automatically and already formatted in the Markdown language. If you view these files, you will notice that the Python script used the templates you downloaded to generate your files, and you can fill in the terms and conditions about your smart contract. You can lay out the guidelines of what exactly your users are purchasing/exchanging and allow better trust between parties; it can include terms and conditions such as intent, warranty, remedies, force majeure, dispute resolution, governing law, and many others. Pay close attention to the terms you set as these can be enforced in a court of law. These terms allow skipping middlemen such as attorneys to have the smart contract set the terms and conditions that both parties agree to. D eploy a Contract To deploy your smart contract to your local testnet network, the set contract command is used to upload the contract. See Figure 6-8 for the expected output. > cleos set contract helloworld ~/Desktop/helloworld -p [email protected] Figure 6-8.  Terminal output of deploying your smart contract 240 Chapter 6 EOS.IO Wallets and Smart Contracts Interact with a Smart Contract Action Now that you have your smart contract deployed on your local blockchain, you can interact with the hello action you created. You will call the hello action and pass your username to the user’s active key. See the output in Figure 6-9. > cleos push action helloworld hello ‘[“john”]’ -p [email protected] Figure 6-9.  Terminal output of push action on a smart contract You can download the entire smart contract project from here: helloworld/. Smart Contact Tokens The EOS.IO GitHub project has a library of smart contracts as examples that can be used. One of these libraries is a smart contract called eosio. token. This contract enables developers to create other tokens as well as transfer a token. You will be using these libraries to create your own tokens. To get started, you will create a new smart contract project and call it eosio.token. > mkdir ~/Desktop/eosio.token && cd $_ C reate Accounts Token gets issued by an “issuer” account. You will start off by creating the “issuer” account and an account called jane that you can use to transfer some tokens. > cleos create account eosio eosio.token [public key] > cleos create account eosio jane [public key] 241 Chapter 6 EOS.IO Wallets and Smart Contracts Compile wasm with the Latest eosio.token Code To issue eosio.token, you will be using the eosio.token.hpp file that defines the contract’s class, actions, and tables, as well as eosio.token. cpp that holds the logic and coding. You can find these files and the entire SmartContract project here: Next, ensure you change the include statement in the CPP code to point to the HPP file you downloaded from GitHub using vim or your favorite text editor. > vim eosio.token.cpp Change the eosio.token.cpp file on line 6 to point to the location of eosio.token.hpp file; in this case, it’s here: include “~/Desktop/eosio.token/eosio.token.hpp” D eploy eosio.token Equipped with eosio.token.hpp and eosio.token.cpp, you have all the files needed. You can compile the latest HPP and CPP files to generate the .wasm code with the eosio-cpp command, just as you did in the HelloWorld smart contract example. > eosio-cpp -o eosio.token.wasm eosio.token.cpp -abigen Next, deploy the eosio.token contract using the set contract command. > cleos wallet unlock -password [DEFAULT_MASTER_KEY] > cleos set contract eosio.token ~/Desktop/eosio.token -abi eosio.token.abi -p [email protected] 242 Chapter 6 EOS.IO Wallets and Smart Contracts Create the EOS.IO Token To create your new token, you utilize the create action. You will be passing the symbol_name type, which includes two parameters. – Maximum supply float: In this example, you’ll set this to 20 million as your max tokens: 20000000.0000. – Symbol: For symbol_name, you need to pick a name. The name must be capital alpha characters only; in this example, select the name TOKEN. The “issuer” account has the authority to make a call issue action or any other actions such as recalling, freezing, and whitelisting owners. To create a new token action, run the following command. See Figure 6-10 for the expected output. > cleos wallet unlock -password [DEFAULT_MASTER_KEY] > cleos push action eosio.token create ‘[ “eosio”, “20000000.0000 TOKEN”]’ -p [email protected] Figure 6-10.  Expected output for creating an eosio.token action You can confirm the tokens were issued by calling the currency stats command. > cleos get currency stats eosio.token TOKEN { “TOKEN”: { “supply”: “0.0000 TOKEN”, 243 Chapter 6 EOS.IO Wallets and Smart Contracts “max_supply”: “20000000.0000 TOKEN”, “issuer”: “eosio” } } Issue Tokens Let’s create another account that you can use to send some of the tokens you issued. We’ll call this account jane. > cleos create account eosio jane [public key] Next, call the “issue” action to issue tokens. In this example, you will issue jane 500 tokens. > cleos push action eosio.token issue ‘[ “jane”, “500.0000 TOKEN”, “move tokens to Jane” ]’ -p [email protected] To see the TOKEN balance in the jane account, you can use the get currency command. > cleos get currency balance eosio.token jane TOKEN 500.0000 TOKEN Transfer Tokens To transfer tokens, you run the transfer action. As an example, let’s transfer tokens from Jane’s account to John’s account. > cleos push action eosio.token transfer ‘[ “jane”, “john”, “100.0000 TOKEN”, “transfer tokens” ]’ -p [email protected] You can confirm John’s account received the tokens by running the currency balance command on both accounts to ensure the math adds up. 244 Chapter 6 EOS.IO Wallets and Smart Contracts > cleos get currency balance eosio.token jane TOKEN 400.0000 TOKEN > cleos get currency balance eosio.token john TOKEN 100.0000 TOKEN Figure 6-11 shows the expected output. Figure 6-11.  Expected output for creating, transferring, and balancing eosio.token actions onnecting to a Public Testnet Block C Producer At the time of writing, EOS.IO provides two public testnets so you can test in a more realistic environment before committing your code to mainnet. – Jungle2.0: – Kylin: I chose Jungle2.0 for the public testnet in this example, but feel free to test both; it’s the same process just with different endpoints. To get started, visit the Jungle project’s GitHub page here: https:// The EOS Jungle testnet is almost identical to your local testnet. You just need to set up the Jungle API endpoint and generate EOS faucet tokens to pay for the account’s creation and RAM usage. 245 Chapter 6 EOS.IO Wallets and Smart Contracts The testnet API endpoint is; just add the endpoint so your previous commands will work. Note  Always test on testnet before publishing your code to mainnet. In September 2018 alone, $240,000 worth of EOS tokens were stolen from EOSBet’s smart contract accounts, and it was because of a smart contracts programming bug that was exploited by hackers and not bugs in the EOS.IO platform itself. You’ll learn more about security in Chapter 10. To create an account, you will generate the two default permissions: owner and active. You can do this at or by running the same command line you used before twice. > cleos create key -to-console Private key: [key] Public key: [key] Next, you need to create an account. You can create an account by visiting the Jungle page and using the public keys you generated: https:// I picked a random name of liontestaa11, but feel free to use any name you want. Just be careful of the strict name restrictions (a-z and 1-5 are allowed only, with a length of 12). If you don’t comply with this strict name restriction, your account won’t get created. See Figure 6-12. 246 Chapter 6 EOS.IO Wallets and Smart Contracts Figure 6-12.  Jungle2.0’s liontestaa11 account was created Notice that you get the same warning as you got on your local testnet regarding the transaction being executed, but it’s not confirmed. To get information about the testnet, you can run the same get info command you ran for your local testnet. Just add the Jungle endpoint URL argument. > cleos -url get info All the cleos commands need the URL endpoint argument; you can edit your bash file to point cleos to the URL you want. Edit the bash profile and point to the public testnet for the block producer, while still pointing to your local machine for the wallet. > vim ~/.bash_profile 247 Chapter 6 EOS.IO Wallets and Smart Contracts Add the following line: alias cleos-testnet=’cleos -url -wallet-url http://localhost:8888′ You did not set the config.ini file here with a custom port, but you are changing the port to 8888. Remember, to run the bash profile to commit the changes, run this: > . ~/.bash_profile Now you can run the all the commands with cleos-testnet. > cleos-testnet get info uy Resource Allocation on the Public Testnet B Block Producer Now you will be publishing your “HelloWorld” smart contract you created in the previous section. If you were publishing your contract on mainnet, you would need to buy RAM and pay to create your account so you could publish your smart contract. EOS tokens are used to purchase resources. In the public testnet, you don’t need to spend actual money for your resources. You get fake faucet tokens that can be used for the Jungle block producer to purchase your resources. To get these tokens, all you need is your account name. Type your account name to get tokens from the Jungle faucet: http://monitor. See Figure 6-13. I’ll explain resource allocation in more detail in the next section when you ready to publish to mainnet. 248 Chapter 6 EOS.IO Wallets and Smart Contracts Figure 6-13.  Jungle2.0 gets tokens through the Jungle faucet You can check the account balance with the get account command; see the output in Figure 6-14. > cleos -url get account liontestaa11 249 Chapter 6 EOS.IO Wallets and Smart Contracts Figure 6-14.  Jungle faucet account balance Now that you have EOS tokens, you can run the cleos system buyram command to purchase RAM so you can publish your smart contract. > cleos -url system buyram liontestaa11 liontestaa11 “10 EOS” ublish Your HelloWorld Contract on the Public P Testnet Now that you have tokens, you can publish your HelloWorld smart contract on the public testnet. Run the set contract command. > cleos -url set contract liontestaa11 ~/Desktop/helloworld You can confirm the code was published using the get code command. You can see the entire expected output in Figure 6-15. > cleos -url get code liontestaa11 250 Chapter 6 EOS.IO Wallets and Smart Contracts Figure 6-15.  Expected output when publishing contract on public testnet Connecting to Mainnet The EOS.IO mainnet is almost the same as the testnet; you just need to use a different API endpoint and actually pay for the accounts and RAM with real EOS tokens. There are three main ways to get EOS tokens: • Mine: This creates a block producer and mines EOS. • Purchase EOS tokens: They can be purchased on crypto exchanges. • Gift: This gets an EOS as a gift from someone. As you saw in previous chapters, creating a block producer and getting selected by the EOS.IO network is not an easy process or guaranteed, and as you just need coins to buy RAM for opening an account and getting resources, you don’t need too many coins. At this point, it’s easy to just purchase these tokens. 251 Chapter 6 EOS.IO Wallets and Smart Contracts You would need to first purchase bitcoin, Ethereum, or other coins on a fiat exchange such as Coinbase,, or Coinmama. Then use exchanges such as Binance or Changelly to change your coins to EOS tokens. The reason is that there is no known exchange available at the time of writing that can directly change your fiat to EOS. Next, you need an endpoint. The 21 selected block producers are able to provide you with an endpoint. You can find all the available block producers and other data regarding the blocks being mined here: – – Once you find a block producer you would like to use, you append /bp.json to the end of the URL to find the endpoint. Here’s an example: The JASON output gives you the block producer’s information and ensures it’s ready for usage. To set the URL, just adjust the -url flag to the block producer you would like to connect to; the rest of the commands are all the same as the public testnet. > cleos -url get info As before, you can edit the bash profile file as you did with the public testnet. alias cleos-mainnet=’cleos -url -wallet-url http://localhost:8888′ Your bash profile should look like this: PATH=”/usr/local/eosio/bin:${PATH}” alias cleos-testnet=’cleos -url -wallet-url http://localhost:8888′ alias cleos-mainnet=’cleos -url -wallet-url http://localhost:8888′ 252 Chapter 6 EOS.IO Wallets and Smart Contracts Confirm it works by running the get info command. > cleos-mainnet get info I’ll spare you from repeating the same steps as in the public testnet section and spending actual tokens on the “HelloWorld” sample smart contract. However, I will cover resource allocation, as you need a good understanding of it to publish smart contracts on mainnet. Resource Allocation Explained I spoke a bit about resource allocation when I covered testnets, as you needed to get EOS tokens to publish your smart contract on a public testnet. For mainnet, you need actual EOS tokens to buy RAM and create your account. There are three types of resources consumed by EOS.IO accounts. – Disk: Bandwidth and log storage (disk) – CPU: Staking computation and computational backlog (CPU) – Ram: Staking state storage Buy RAM on Mainnet To free up RAM, you need to delete data from the account state mechanism, and then the RAM can be sold on the RAM marketplace at the current RAM price. The RAM marketplace price can be found here: 253 Chapter 6 EOS.IO Wallets and Smart Contracts Create an EOS.IO Account on Mainnet EOS.IO accounts are necessary, as they are needed to interact with the EOS.IO network and create an account. As I explained previously, someone who already has an account needs to vouch for creating new accounts. If you don’t have someone with an EOS account who can create your account, you can get an account created with third-party providers. The third-party providers normally charge you a fee. For instance, you can download EOS Lynx on your phone and pay $2 to create an EOS.IO account. Change Your Account’s Public and Private Keys Once you get a mainnet account, you are not done. You need to make sure you change your private key before funding your account, as the service that creates your account could just store your private keys and take your funds. You are already familiar with all these steps; the only new command here is remove_key, which removes the old key from your wallet. You create a new key, unlock your wallet, reset the permissions with the new key, and remove the old public key as well as import the new private key. Follow these steps: > cleos create key > cleos wallet unlock > cleos set account permission [ACCOUNT NAME] active [PUBLIC KEY] owner -p [ACCOUNT NAME]@owner > cleos set account permission MYACCOUNT owner [PUBLIC KEY] -p [ACCOUNT NAME]@owner > cleos wallet remove_key [OLD PUBLIC KEY] > cleos wallet import [PRIVATE KEY] 254 Chapter 6 EOS.IO Wallets and Smart Contracts CPU and Bandwidth Allocations To get bandwidth and CPU, you need to allocate EOS tokens, and the resource will be available automatically for you proportional to the amount held in the staking contract period. For instance, during the staking window, say you would like to consume 1 CPU unit. To do so, you would need to compete with other accounts so you have 0.1 percent of all CPU-staked tokens under your account or have someone else delegate these tokens to your account. After the staking period, the consumed resources free up, and you can reuse the same staked tokens, so there’s no need to keep purchasing more EOS tokens each time. The EOS tokens can be undelegated after you are done. W here to Go from Here EOS.IO offers an online resource with links; see The developer resource provides valuable documentation as well as information about other tools I did not cover such as these: – State handler: demux-js – JavaScript library: eosjs I also recommend exploring the EOS GitHub smart contracts examples, which can help you learn about all the functionally and what’s possible with EOS.IO. S ummary In this chapter, I covered the EOS.IO blockchain in more detail. You set up a local testnet environment by installing the EOS.IO and EOSIO.CDT libraries and learned how to configure keosd and nodeos. You learned 255 Chapter 6 EOS.IO Wallets and Smart Contracts about EOS.IO wallets, including how to create, delete, and back up wallets as well as how to create a wallet with custom names and perform operations such as opening, locking, and unlocking a wallet. Next, I covered a wallet’s key pairs and how to spin and re-spin up a local node (nodeos) to run a local block producer. You learned about active and owner permissions as well as single-signature (single-sig) and multisignature (multisig) are accounts. To understand EOS.IO smart contracts, you created a “HelloWorld” smart contract and tokens by first creating accounts and then writing C++ code. You then compiled and generated WebAssembly and ABI files as well as Ricardian contracts. You then learned how to deploy the contracts you created and interact with them. Once your tokens were generated, you were able to issue and transfer tokens between accounts. You continued by connecting to a public testnet block producer to test your smart contracts in a more realistic environment, and lastly you learned how to connect and publish on mainnet and learned about resource allocations on an EOS.IO network. In the next chapter, I will cover NEO blockchain wallets and NEO smart contracts. 256 NEO Blockchain and Smart Contracts In Chapter 1, I covered the NEO proof of stake (PoS) blockchain consensus mechanism. In Chapter 2, you created a NEO bookkeeping node on AWS Ubuntu and learned how to request a consensus authority certificate and get elected as a bookkeeper. In this chapter, I will expand on the NEO blockchain, and you will learn how to set up a local environment, do operations in NEO wallets, create smart contracts (NeoContracts), and publish. In this chapter, I will cover NEO’s blockchain high-level architecture and how to set up your local environment, create a local testnet chain, create “Hello, World” projects in both C# and Python, publish these smart contracts, and learn the criteria to compare Ethereum versus EOS versus NEO. As you can see, understanding smart contracts, blockchain, and the process of publishing is similar between projects, and covering three projects is sufficient to gain an understanding of how to work with the rest of the 40 (at the time of writing) projects available for writing smart contracts that are out there. Chapter 7 NEO Blockchain and Smart Contracts NEO’s High-Level Blockchain Architecture NEO was founded in 2014 with the name of AntShares by Da Hongfei and Erik Zhang and then was open sourced on GitHub in June 2015 with the name of NEO. The NEO consensus mechanism is called Byzantine Fault Tolerant (dBFT), which is a modified PoS. This type of mechanism makes NEO a scalable blockchain. Bookkeeping nodes are randomly selected to validate transactions and can support up to 10,000 transactions per second. “NEO is a non-profit community-driven blockchain project. It utilizes blockchain technology and digital identity to digitize assets and automate the management of digital assets using smart contracts. Using a distributed network, it aims to create a ‘Smart Economy’. ” — NEO transactions are charges with NEO gas tokens. The NEO genesis block includes 100 million NEO. Half were sold to early investors, and half were locked in NEO smart contract tokens. Each year 15 million NEO tokens are unlocked to be used for the NEO development team to fund development goals. NEO charges fees for transactions as well as a smart contract’s related transactions. The NEO fee structure related to smart contracts is listed in the NEO white paper: In term of programming languages, NEO smart contracts support the NeoVM (NEO’s Universal Lightweight Virtual Machine) compiler,, Java, Kotlin, Go, and Python. Here are some notable NEO development features: – NEO can create smart contract tokens built with the Communications Standard (NEP5). These tokens are able to communicate with other NEO tokens. – Smart contracts can communicate with other blockchains (this feature is called NeoX). 258 Chapter 7 NEO Blockchain and Smart Contracts – NEO can pass information via a file sharing protocol (called NeoFS). – It uses a lattice-based cryptographic mechanism called quantum-safe (NeoQS). NEO’s “smart economy” infrastructure (I will explain this concept in the next section) enables smart contracts to support front-end applications and integrate with other smart contracts and other blockchains through an open API. NEO’s open API allows you to integrate data from external sources. Figure 7-1 shows a high-level architecture diagram of the NeoVM. The NeoVM core is the deployment box (the dashed box). As you can see, the external data with the execution engine (green box) enables smart contracts to interact and perform operations. Then data can be stored on the NEO distributed ledger. “We hope the platform can be used for different front end ­scenarios, such as the Digital asset wallet, Forum, Voting, Profile management and Mobile applications. The platform also features an open API that can be used for integration with other systems.” —Da Hongfei, Zhao Chen founder of NEO 259 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-1.  NEO’s virtual machine architecture diagram. Image credit: What Is NEO’s Smart Economy? NEO coined the term smart economy, which explains NEO’s vision. This vision consists of changing your existing market from a traditional economy to the smart economy with the power of a decentralized blockchain. To achieve this goal, NEO integrates digital assets, digital identities, and smart contracts into its platform. 260 Chapter 7 NEO Blockchain and Smart Contracts Note  NEO’s smart economy vision is aimed to change the way existing markets work, from a traditional economy to a “smart economy,” with the power of a decentralized blockchain. This is achieved by integrating digital assets, digital identities, and smart contracts. NEO’s smart economy concept consists of integrating the following three components: – NEO digital assets: These assets contain electronic data and can be programmed. Placing the digital assets on a blockchain provides the benefit of PoS blockchains, such as decentralization, trust, traceability, and transparency. The NEO blockchain enables users to register, trade, and transfer different types of assets. Physical assets get digitization through digital identity; then these digital assets can be protected by law through validation. For an ICO, it costs 5,000 gas to register a digital asset. Then there is a renewal fee of 5,000 gas per year. – NEO digital identity: This is the digitization of the identity of individuals, organizations, or any other entities. A NEO digital identity is based on the public key infrastructure (PKI) X.509 standard implementation that also supports web of trust pointto-point certificates. – NEO smart contract: Smart contracts on NEO are called NeoContracts, and they support the C#, VB.NET, F#, Java, Kotlin, and Python languages. Supporting these languages gives the benefits of having sophisticated development, debugging, and compilation in the Visual Studio, Eclipse, and WebStorm IDEs. NeoVM is built for scalability. 261 Chapter 7 NEO Blockchain and Smart Contracts Setting Up Your Local Environment As mentioned, NEO supports enterprise-level programming languages such as C#, VB.NET, F# Java, Kotlin, and Python. This selection of programming languages gives NEO an advantage in building NeoContracts because you can utilize the Visual Studio 2017 IDE, which offers enterprise tools for development. In this chapter, I will be using the following .NET tools: – Visual Studio 2017 IDE: To follow along, install the Visual Studio (VS) Community Edition for Mac. – .NET Core: To follow along, install .NET Core to be able to publish DLL library files. In addition to .NET, you need the following tools: – Xcode 10.1: You need Xcode 10.2 for the tools and libraries you will be installing. – Docker: Docker is a popular tool for creating containers and integrating software. You will be using Docker for your private net to run a whole NEO blockchain to simulate four consensus nodes in a single, lightweight Docker container. – neo-compiler: The NEO compiler is needed to turn your code to an .avm file that can be deployed on the NEO blockchain. – neo-cli: You will install and use the NEO command-line tools for wallets, operations, and RPC calls to the NEO API. Now that you know what needed, let’s get started. 262 Chapter 7 NEO Blockchain and Smart Contracts X code 10.2 At the time of writing, you need Xcode with at least version 10.1 for the tools and libraries needed for NEO. The latest Xcode at the time of writing is Xcode 10.2.1. You can check whether you already have Xcode installed via the command line. > xcodebuild -version Xcode 10.1 Build version 10B61 This command will output the version if Xcode is installed. If you need to upgrade or install, visit the Apple developer portal: https://developer. Install Visual Studio 2017 IDE Next, download and install the latest version of Visual Studio (VS) Community Edition for Mac. The community edition is free and can be downloaded from the following URL: com/vs/community/. For future reference, to uninstall a portion or all of VS, follow the instructions here: mac/uninstall#net-core-script. The complete VS 2017 consumes a lot of disk space; however, you don’t need all the packages downloaded. You need only Xamarin Workbooks in order to develop NeoContracts, so only download what’s needed. During the installation process, the wizard gives you an option of what platforms and tools to install. Select Xamarin Workbooks by clicking the checkbox and click the Install button. See Figure 7-2. 263 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-2.  Visual Studio Community Edition for Mac install wizard Install .NET Core You will be installing .NET Core so you will be able to publish DLL libraries files via the command line. This will be done via the dotnet publish command. To download it, go to the dotnet Microsoft site; see Figure 7-3. 264 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-3.  Downloading Microsoft dotnet core You will be downloading both: Build apps – SDK v2.2.101 and Run apps – Runtime v2.2.0. To confirm the installation went well, run the dotnet -version command. > dotnet -version 2.2.101 This command will output the dotnet version, which at the time of writing is 2.2.101. If the SDK is not installed, you will get the following error message: Did you mean to run dotnet SDK commands? Please install dotnet SDK from: 0x409 You can also output your machine info via the info command. > dotnet -info 265 Chapter 7 NEO Blockchain and Smart Contracts I nstall Docker Next, you will install Docker. Docker is needed to create a container that you will be using to create your local blockchain. – Download Docker from here: beta/Docker.dmg – Installation instructions: install-docker-on-macos Once Docker is downloaded and installed, double-click Docker from the Applications menu to get Docker running. You will see the Docker icon in the top menu on your computer. You can verify it’s installed correctly by typing docker at the command line; it lists the Docker commands. > docker Run docker ps to view containers running to ensure you do not get any error messages. > docker ps If Docker is not running, you will get the following message: Cannot connect to the Docker daemon at unix:///var/run/docker. sock. Is the docker daemon running? Just open Docker in case you get this message. Additionally, if your container is not running but it was already created, you can use the -a (all) flag and find the container ID. > docker ps -a List containers Then when you have the container ID, you can start that container. > docker start [CONTAINER ID] 266 Chapter 7 NEO Blockchain and Smart Contracts For now, you won’t see any list of containers as you have not created your containers yet. Download NeoCompiler and Generate neon.dll To create your NeoContract, you need to generate an .avm file. To do so, you need to create a neon.dll file to be able to generate the smart contract. To get started, you will clone the neo-compiler to your desktop and then generate the neon.dll file. > cd ~/Desktop > git clone > cd ~/Desktop/neo-compiler/neon/ To publish your self-contained .avm file, you need to set a runtime identifier. You can set the neon.csproj runtime identifier to the correct OS. As I am using a Mac and not a PC here, I need to change the neon.csproj file. To follow along, first make a copy of the original. > cp neon.csproj neon.csproj.backup I am using vim, but feel free to use your favorite editor. > vim neon.csproj Once the file is open, replace the following configuration, which sets a target framework. Note  You can compare your output and settings with my project here: chapter7/NEO/neo-compiler/neon/. Also, you can find neon.csproj there. 267 Chapter 7 NEO Blockchain and Smart Contracts 2016-2017 The Neo Project Neo.Compiler.MSIL The Neo Project netcoreapp2.0 anycpu neon Exe Neo.Compiler.MSIL osx.10.12-x64 Neo.Compiler The Neo Project Neo.Compiler.MSIL Neo.Compiler.MSIL RELEASE;NETCOREAPP1_0 none False true true 268 Chapter 7 NEO Blockchain and Smart Contracts Now publish pointing to the runtime identifier osx.10.11-x64 by passing the RuntimeIdentifier setting param. > dotnet publish -r osx.10.11-x64 The compiler created your neon.dll file here: bin/Debug/netcoreapp2.0/osx.10.11-x64/publish/neon.dll See Figure 7-4 for the output. Figure 7-4.  Compiling neon.dll for the target osx.10.11-x64 neo-cli to Generate a NEO Node Next, you want to create a fill NEO node. To generate a full NEO node, there are two full-node options. – neo-gui: This can be used by both developers and NEO users. It can be used to do basic user-client operations such as managing wallets but also publishing smart contracts. It has a visual user interface. However, it works only on Windows at the time of writing. 269 Chapter 7 NEO Blockchain and Smart Contracts – neo-cli: This provides an external API for basic wallet operations. It also helps other nodes keep a consensus with the network and generate new blocks. In this case, I am installing on a Mac, so you will be using neo-cli to manage your wallet via the command line. However, it’s good for you to know that you can install neo-gui and create a virtual PC that way. n eo-cli For neo-cli, you need to install the LevelDB package as it’s a dependency. As you recall, you already installed LevelDB in Chapter 3 via Homebrew. If you did not install LevelDB previously, here is the command again: > brew install leveldb Alternatively, you can check if you have it and upgrade. > brew upgrade leveldb Next, clone neo-cli to your desktop. > cd ~/Desktop > git clone Now, you can use dotnet to publish neo-cli from the source code you downloaded. > cd neo-cli > dotnet restore > dotnet publish -c Release The .dll file should be created in the Release folder; see Figure 7-5 for the output. 270 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-5.  Building the neo-cli DLL Note  You can compare your output and settings with my project here: chapter7/NEO/neo-cli. To run the .dll file, you use dotnet and the location of the DLL file, which starts a NEO command-line terminal. > cd bin/Release/netcoreapp2.1/ > dotnet neo-cli.dll. neo-cli also supports plugins. For instance, you can enable logs in neo-cli with application logs, or you can improve security in RPC nodes via RPC Security. A list of plugins can be found here: https://github. com/neo-project/neo-plugins. Create a Local NEO Private Testnet You can run your NeoContracts on public testnets just as you have done with other blockchains; however, it’s much better to run your own private testnet so you have full control of it. A private testnet can be on the cloud, but you will have to pay for the service provider, so it’s better if you set up your testnet on your local box. 271 Chapter 7 NEO Blockchain and Smart Contracts As evident by the documentation, the tools for NEO were primarily developed for PC users. However, because of the tools developed by the City of Zion community (CoZ,, running a private chain is possible on any platform with Docker and Python. The steps you need to take to run a local NEO private testnet are as follows: 1. Install neo-python: This allows you to run a full NEO node and to interact with the blockchain. 2. Create neo-privatenet-docker: This allows you to run a whole NEO blockchain with four consensus nodes in a single, lightweight Docker container. 3. Create a NEO wallet: This connects to the private net and creates a wallet. 4. Claim: This is initially 100,000,000 NEO. 5. Bootstrap the testnet: This synchronizes the network. P ython 3.6 neo-python needs Python 3.6 or later. Mac comes out of the box with Python, and you can verify you have python3 installed via the -version command. > python3 -version Python 3.6.x If you are running a previous version of Python and need to install/re-­ install Python, follow these steps: > brew unlink python 272 Chapter 7 NEO Blockchain and Smart Contracts Next, install Python with Brew. > brew install -ignore-dependencies f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.rb Now switch the Python versions. > brew switch python 3.7.0 > brew switch python 3.6.5_1 In case you don’t have pip installed, run this: > curl -O > sudo python > pip Install neo-python Next, clone neo-python from the City of Zion and check out the development branch. > > > > cd ~/Desktop git clone cd neo-python git checkout development You can create a virtual environment using Python 3.6 and then run the activate script. > python3.6 -m venv venv > source venv/bin/activate Ensure you have the latest pip version by running this command: (venv)> pip install -upgrade pip 273 Chapter 7 NEO Blockchain and Smart Contracts Now you can install the package in an editable form. (venv)> pip install -e. You can compare your output with mine; for the steps you took so far, see Figure 7-6. Figure 7-6.  neo-python installation output To confirm the installation went well, run the -version command. At the time of writing, it outputs version 0.8.3. > np-prompt -version neo-python v0.8.3-dev Now you can open a NEO bash with the np-prompt command. To exit bash, run the exit command. > np-prompt neo>exit 274 Chapter 7 NEO Blockchain and Smart Contracts I nstall neo-privatenet-docker You already installed Docker, so now you can create a Docker container that will create four NEO nodes to create a private testnet. Go ahead and install the Docker container on your desktop and build the files, as shown here: > cd ~/Desktop > git clone­ docker.git > cd neo-privatenet-docker >./ After the image is built, you can start a private network like this: >./ Successfully built #build number Note If Docker needs to be restarted or is not running, run the following command:  > ./ Start a Network and Claim Initial NEO and Gas Next, you will start your private network, create your wallet, and claim the initial NEO and 40 gas. This is done by running the docker_run_and_ script. You can see the output in Figure 7-7. > ./ 275 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-7.  docker_run_and_create_wallet script output Once the process is completed, you can get a confirmation of the two files that were created (see Figure 7-7). – neo-privnet.wallet: This file is a wallet that you can use with neo-python. – neo-privnet.wif: This file is a WIF private key you can import into other clients, such as neo-gui. These files give you access to the wallet containing the NEO and gas for your private network. The script automatically claimed the NEO and gas for you. You can check Docker and see the neo-privnet container running, as shown in Figure 7-8. > docker ps Figure 7-8.  neo-privnet Docker container running 276 Chapter 7 NEO Blockchain and Smart Contracts B ootstrapping the Testnet Now that you have a private testnet running, you need to bootstrap the testnet blockchain database. This synchronizes the network and is done by running np-bootstrap. This can take a while; once completed, you will get confirmation. > np-bootstrap -n confirm Successfully downloaded bootstrap chain! Notice that you use the -n flag to get database notifications. Start NEO Bash Now that you have your private testnet container running with four nodes and you bootstrap your testnet database, you can start a neo-cli bash by calling the command. > cd ~/Desktop/neo-python/neo/bin > python3.6 -p Once you run this command, the NEO bash opens, and you can use the state command to view information about the blockchain, as shown in Figure 7-9. neo> state 277 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-9.  Information about your blockchain via the state command neo-cli offers access to many RPC calls via the NEO API; however, the wallet needs to be open to run these commands. You can open your wallet with the wallet command and the file location. This command will ask for the wallet’s password. For the password, use coz. neo> wallet open ~/Desktop/neo-privatenet-docker/neo-privnet. wallet password: coz Next, rebuild the wallet and call the wallet command. You will see the NEO and NeoGas fake testnet coins available (see Figure 7-10). neo> wallet rebuild neo> wallet 278 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-10.  neo-privnet wallet showing claimed coins To close the wallet and exit bash, use the wallet close command and exit. neo> wallet close neo> exit You have succeeded in creating a private NEO blockchain running on a testnet with 100 million NEO and 40.0 NeoGas claimed coins that you can use for development. Potential Problems During Installation NEO feels like chasing a moving target at times. In fact, it’s likely that by the time you are utilizing the instructions in this book, the code won’t work as expected because of changes in NEO. Moreover, during installation, there 279 Chapter 7 NEO Blockchain and Smart Contracts are some potential problems that you can encounter. I suggest you check the latest information here: C lean Database If you need to clean the neo-python database to bootstrap and sync again, run the following command: > rm -rf ~/.neopython/Chains/privnet* b ’Corruption Message If you are getting a “b’Corruption: corrupted compressed block contents” message, you need to re-install LevelDB. > brew reinstall leveldb R estart Docker It’s good to know how to restart Docker in case you need to restart your computer, upgrade the Docker version, or upgrade the container files. To restart Docker, select Docker from the top menu and click Restart (see Figure 7-11). The state is deleted (the whole “old” blockchain will be gone), and you should also remove Chains/privnet from neo-python and any privnet wallets you created. > > > > rm ~/Desktop/neo-privatenet-docker/*.wallet rm ~/Desktop/neo-privatenet-docker/*.wif rm -rf ~/.neopython/Chains/privnet* docker ps 280 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-11.  Docker top menu icon restart button NEO “Hello, World” You have your local private testnet environment and NEO tools set up on your machine, so now you are ready for the development of your NeoContract project. You can develop in different languages, and the process is similar. I will show you the code in C# as well as Python. I have kept the code to a simple working “Hello, World” example, but once you are able to get to this point, you can experiment with the different features NEO has to offer. Follow these steps to create and publish your code: 1. Building the NeoContract framework: Generate a Neo.SmartContract.Framework.dll file. 2. Create a NEO “Hello, World” Project: Create your #C contract project. 3. Code a NEO “Hello, World” smart contract in C#: Code your minimalistic example in C#. 4. Code a NEO “Hello, World” smart contract in Python: Code your minimalistic example in Python. 5. Publish: Publish your contract to your private testnet chain. 281 Chapter 7 NEO Blockchain and Smart Contracts uilding the NeoContract Framework: Neo. B SmartContract.Framework.dll The first step is to create a file that holds the NeoContract framework code that you need to include in your NeoContract in order to access the NEO features. To build your NeoContract, you will be downloading and installing the NEO Development Pack. You will place these tools on your desktop for easy access. Note that you can always move the files to a better location later. Navigate to the desktop and clone the neo-devpack-dotnet project. > cd ~/Desktop > git clone Next, run the neo-devpack-dotnet.sln file by double-clicking it or run the Terminal open command. > open neo-devpack-dotnet.sln VS opens, and you should expect to get three error messages. Click OK to dismiss these messages, as these errors will not affect building your project. In the left window, you can see the Solution tab, as shown in Figure 7-­12. Expand “neo-devpack-dotnet (master)” if it’s not expanded. Next, right-click Neo.Smartcontract.Framework and choose Build Neo. Smartcontract.Framework. See Figure 7-12. 282 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-12.  Building the Neo.SmartContract.Framework project Once the build is completed, you will get a “Build successful” message in the VS output’s top middle window. You can also find the Neo. Smartcontract.Framework.dll file here: > cat ~/Desktop/neo-devpack-dotnet/Neo.SmartContract.Framework/ bin/Debug/netstandard1.6/Neo.SmartContract.Framework.dll The .dll file is a .NET Intermediate Language (IL) language file that you will include in your library to have access to the NeoContract framework code. Neo.SmartContract.Framework does not support the full set of C# features because of the differences between the NeoVM and the C# IL file. 283 Chapter 7 NEO Blockchain and Smart Contracts Create a NEO “Hello, World” Project Now that the Neo.Smartcontract.Framework.dll file is ready to be used, you can create your project and include the NEO framework as a dependency. To get started, open Visual Studio. Select File ➤ New Solution… ➤ New Project wizard opens up. In the left menu, select Library ➤ .NET Standard Library. Next, select .NET Standard 2.0 for the .NET Core version and then click Next. See Figure 7-13. Figure 7-13.  New Project template wizard The configure wizard opens with a new project window. Call the project hello_contract, leave the default settings and click the Create button. See Figure 7-14. 284 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-14.  VS create new project wizard Once the project is created, you need to attach the file Neo. Smartcontract.Framework.dll as a dependency. To do that, right-­ click the Dependencies folder in the Solution menu and then click Edit References. See Figure 7-15. 285 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-15.  “Hello, World” project dependencies edit reference In the Edit References window, go to the .NET assembly tab. Choose Browse and add the Neo.Smartcontract.Framework.dll file located here: ~/Desktop/neo-devpack-dotnet/Neo.SmartContract.Framework/bin/ Debug/netstandard1.6/Neo.SmartContract.Framework.dll Next, click Open, as shown in Figure 7-16. Select the Neo. SmartContract.Framework.dll checkbox and click Ok. 286 Chapter 7 NEO Blockchain and Smart Contracts Figure 7-16.  VC edit references .NET assembly oding the NEO “Hello, World” Smart Contract C in C# In this section, you will be using C# to develop your NEO “Hello, World” smart contract in .NET. The NeoVM is more compact; you can compile only limited C#/dotnet features into your AVM file. You can view the list of features available for development here: sc/quickstart/limitation.html. The examples will use the “Hello, World” example provided in the NEO examples. using Neo.SmartContract.Framework; using Neo.SmartContract.Framework.Services.Neo; public class Class1: SmartContract { public static void Main() { Storage.Put(Storage.CurrentContext, “Hello”, “World”); } } 287 Chapter 7 NEO Blockchain and Smart Contracts After writing the code, select Build from the top menu and then Build All (or Command+B) to compile the Class1.cs code. The .dll library file was created in the bin/Debug/netstandard2.0/ folder. You will use this .dll file with the neo-compiler and convert the .dll file to an AVM file. After compiling the DLL file, the hello_contract. dll file is created here: ~/Projects/hello_contract/hello_contract/obj/Debug/ netstandard2.0/hello_contract.dll Note The NeoContract framework generates the NeoVM bytecode. The code is saved in the AVM file format. The *.avm file can then be deployed on the NEO blockchain. oding the NEO “Hello, World” Smart Contract C in Python Like in #C, you can generate some minimalistic Python code to print “Hello, World.” You can use the Eclipse IDE ( ide/) or any editor of your choosing. These instructions will be using vim. Create a file named > vim ~/Desktop/smartContracts/ Type the following code to print “Hello World.” def Main(): print(“Hello World”) return True To close and save the file, type :wq in vim. 288 Chapter 7 NEO Blockchain and Smart Contracts Compiling Your Smart Contracts to .avm Now that you have two files named and hello_contract.dll, the next step is to compile these files into NEO virtual machine files (.avm) that you will deploy on the NEO blockchain. Let’s start by compiling the hello_contract.dll file. Change the directory to the DLL file. > cd ~/Desktop/neo-compiler/neon/bin/Debug/netcoreapp2.0/ osx.10.11-x64/publish Copy Neo.SmartContract.Framework.dll. > cp ~/Projects/hello_contract/hello_contract/bin/Debug/ netstandard2.0/Neo.SmartContract.Framework.dll ~/Projects/ hello_contract/hello_contract/obj/Debug/netstandard2.0 Now, you can use the dotnet core tool to publish your DLL into an AVM file, as shown in Figure 7-17. > dotnet neon.dll ~/Projects/hello_contract/hello_contract/obj/ Debug/netstandard2.0/hello_contract.dll You can see the output, as shown in Figure 7-17. Figure 7-17.  Converting a DLL into AVM bytecode You can see the AVM bytecode file using the ls command. > ls ~/Projects/hello_contract/hello_contract/obj/Debug/ netstandard2.0/∗.avm hello_contract.avm 289 Chapter 7 NEO Blockchain and Smart Contracts Similarly, you can compile the Python file into AVM. In NEO bash, use the sc build command. > cd ~/Desktop/neo-python/neo/bin > python3.6 -p neo> sc build ~/Desktop/smartContracts/ Saved output to ~/Desktop/smartContracts/sample1.avm ublish a Smart Contract on a Private P Testnet The next step is to deploy your AVM files to the NEO private testnet chain. You don’t need to remember all the options. You can call the command with the help flag to see the options. neo> sc deploy help Deploy a smart contract (.avm) file to the blockchain Usage: sc deploy {path} {storage} {dynamic_invoke} {payable} {params} (returntype) path – path to the desired Python (.py) file storage – boolean input to determine if smart contract requires storage dynamic_invoke – boolean input to determine if smart contract requires dynamic invoke payable – boolean input to determine if smart contract is payable params – input parameter types of the smart contract returntype – (Optional) the return type of the smart contract output For more information about parameter types see data-types.html#contractparametertypes 290 Chapter 7 NEO Blockchain and Smart Contracts Next set storage, dynamic_invoke, and payable as false, and set params and returntype as 01, as shown in Figure 7-18. neo> sc deploy ~/Desktop/smartContracts/sample1.avm False False False 01 01 Figure 7-18.  Publishing an AVM file on a private testnet chain NEO asks for a contract name; let’s call the contract helloWorld. Leave the version, author, email, and description fields blank and enter your wallet password to pay for the contract. 291 Chapter 7 NEO Blockchain and Smart Contracts P ublishing to Mainnet To publish on mainnet, you can use the same process as you did with the testnet; just bootstrap to the mainnet. B ootstrapping to Mainnet To bootstrap to the mainnet blockchain, just run np-bootstrap with the -m flag (it’s close to 10 GB). You can also use the notifications database on mainnet. > np-prompt -m -n Installing the neo-gui Client An easier approach is to set and publish a NeoContract through neo-gui. You need to set up a virtual machine for PC, but deploying AVM files is a breeze. Follow these instructions: E thereum vs. EOS vs. NEO : Smart Contracts Developer Perspective Showdown At this point, I have covered three major blockchains for developing smart contracts, and it’s hard not to compare them. However, there are so many factors to take into account when comparing these three blockchains. Additionally, at the time of writing, there are more than 40 blockchain projects that you can choose from for the deployment of smart contracts. Each project has pros and cons, and it’s beyond the scope of this book to cover all of them. Instead, I will be focusing on specific criteria to try to 292 Chapter 7 NEO Blockchain and Smart Contracts help you understand what factors to consider when selecting a platform out of the three I have covered so far. There is an organization that tries to rate these different blockchains; it’s called the China Center for Information Industry Development (CCID). CCID utilizes contributions from professors and researchers at China’s most prestigious educational institutions including Tsinghua and Beijing University to take into account features, adoption rates, and many other indicators to rank each blockchain. However, these ratings change often, and you should check the latest blockchain ratings on the web site: Note that at the time of writing, EOS and Ethereum have been maintaining their dominance for the fourth consecutive time on the CCID list. Further, determining what blockchain to utilize to publish smart contracts should take into account more factors, such as your team’s ability, funding, the number of needed transactions, the number of accounts needed, wallets, exchanges, and much more. Another major indicator to consider in determining the health of a blockchain is the user and developer adoption. You can find the current number of dapps for different smart contract platforms by checking these sites: – EOS: – Ethereum: – NEO: Looking through the list of dapps, keep in mind that although there are 6,050 dapps listed on at the time of writing, there are only 106,938 users, which indicates that few dapps are being used and mass adaptation is not here yet. Additionally, note that this comparison holds true at the time of writing and is based on my opinion. You should do your own research and due diligence before selecting the ideal blockchain to fit your smart contract needs. Table 7-1 provides the comparison. 293 Chapter 7 NEO Blockchain and Smart Contracts Table 7-1.  Etherum vs. EOS vs. NEO Smart Contracts Comparison Category Ethereum EOS NEO Adoption Currently holds the crown Steady increase in adoption Least adopted out of the three CCID ranking Rank #2 Rank #1 Rank #5 Consensus mechanism PoW DPoS dBFT Transactions per second 15 Millions 10,000 transactions per second Dapp deployment cost Minimum fee of ~120 EOS 32,000 gas, plus 200 gas per byte of the source code Fixed cost of 100 to 1,000 gas ICO costs 5,000 gas to register digital asset; renew fee of 5,000 gas per year Transaction cost $0.05 to $3.5 $0 (however, creating a new account costs $1 to $4 per account paid by application developers) Initial 10 gas execution free, fees for system calls and instruction (see white paper) Scalability No; await hard fork Yes Yes Dev tools Mature development tools from project and community, including tools for development frameworks, IDEs, communicating, and test tools Dev tools could use an Mature development upgrade; debugging tools still done utilizing caveman debugging (continued) 294 Chapter 7 NEO Blockchain and Smart Contracts Table 7-1.  (continued) Category Ethereum EOS NEO Docs Well documented by both project and community Developers. EOS.IO docs and community tutorials are not keeping up with EOS.IO GitHub changes; many GitHub issues regarding installation Projects docs (http://docs. and community tutorials Community support The Ethereum Community Fund (ECF) with organization support: Microsoft, Intel, Amazon, J.P. Morgan, and even government involvement Committed $1 billion in funds focused on the growth of the EOS ecosystem Has run and supported more than 100 community events Development languages Solidity, Bamboo, Vyper, LLL, Flint C, C++ C#, VB.NET, F# Java, Kotlin, and Python; future plans to support more languages Market cap $14,068,553,166 USD $2,341,702,969 USD $488,507,580 USD Number of dapps 1,324 226 Less than 100 (continued) 295 Chapter 7 NEO Blockchain and Smart Contracts Table 7-1.  (continued) Category Ethereum EOS NEO Wallet Desktop and hardware wallets, more options than EOS and NEO Desktop and hardware wallets Desktop and hardware wallets Large exchange support Available on all major Not supported yet exchanges on many major exchanges such as Coinbase Not supported yet on many major exchanges such as Coinbase Turing complete Yes No No This list summarizes the Ethereum, EOS.IO, and NEO Blockchain platforms’ pros and cons: – Ethereum’s biggest pro is that it was the first and most popular smart contract platform and has the most developers, third-party tools, support, documentation, and support community. The biggest downside is the Ethereum scalability issue of using PoW; there is a hard fork in the works at the time of writing to remedy this downside and move Ethereum to PoS. Another downside is the cost of 200 gas per byte for source code; this is pricey if your code is not optimized, especially as you need to constantly republish your code. Lastly, the support for less popular programming languages such as Solidity is less than ideal. – EOS’s advantage is its scalability and ability to run millions of transactions per second with no change, 296 Chapter 7 NEO Blockchain and Smart Contracts as well as faster code execution using WASM. EOS supports C and C++, and the actual blockchain coded in C++ gives it an advantage as C has a larger developer base than Solidity. However, EOS has a long way to go in terms of adoption, providing $1 billion funding can be useful for companies and individuals with the right idea. Its high ratings and great features are not enough to replace Ethereum in dominance it claims to be. Only time will tell. – NEO supports major programming languages (C#, VB.NET, Java, and Python), giving it a big advantage as a large number of developers can code with a smaller learning curve. Additionally, the efficient and inexpensive computationally execution of contracts is an advantage; however, NEO has the smallest community support out of the three platforms, and the stiff 5,000 NeoGas to register digital assets yearly may be a buzz killer for many potential projects. W here to Go from Here Try these resources: • Read the NEO docs here: The site includes tutorials for sample NeoContracts, creating NEO nodes, NEO utilities, white papers, and more. • Visit to find NEO wallets from third parties. 297 Chapter 7 NEO Blockchain and Smart Contracts • For debugging, check Neunity.Adapter or Neo-­Debugger to write test cases and run source code in the IDE:­ tools/releases. • Create additional NeoContracts and include SmartContractEvent, which gets dispatched through neo.EventHub; subscribe and test your contracts. S ummary In this chapter, I covered the NEO blockchain and NEOContracts. You looked at NEO’s high-level blockchain architecture and learned about NEO’s smart economy. You set your local environment and upgraded Xcode, installed Visual Studio 2017 IDE, and installed .NET Core. You installed Docker, so you can now create containers, and you downloaded neo-compiler and generated neon.dll. Lastly, you built the neo-cli so you can manage your wallet and run other RPC operations. Next, you created a local NEO private testnet by installing neo-python and neo-privatenet-docker. You bootstrapped the testnet and started NEO bash and were then able to start your network and claim NEO and gas. Additionally, I covered potential problems during the installation of your NEO tools. Next, you created two “Hello, World” projects, one in C# and one in Python, and were able to compile these projects into the NEO virtual machine’s bytecode (AVM) files. You took these files and learned how to publish them on the NEO testnet blockchain as well as on the NEO mainnet. Lastly, I compared Ethereum versus EOS versus NEO to help you better understand the differences between these platforms as well what criteria to look at when selecting a platform for your smart contracts. 298 Hyperledger In previous chapters, I covered blockchain technologies that are focused on cryptocurrency, and in fact, each project I have covered so far has included its own currency. Hyperledger is different; it does not have a currency attached, although you can create a coin if needed. Instead, Hyperledger was created with the aim of being an open source platform targeted at utilizing blockchain to fit business needs. Hyperledger started in 2015 as an open source blockchain contributed by Digital Asset and IBM as a result of a hackathon (now the blockchain is called Hyperledger Fabric), and it extended to consists of multiple pluggable modules and the entire project is called Hyperledger aimed at improving a blockchain’s performance and reliability so you can assemble modules to create your own unique platform to fit your business needs. Note  The Hyperledger project is an umbrella strategy modular architecture consisting of a collection of pluggable components that are used to create custom blockchain solutions for businesses. The Hyperledger architecture aims to provide scalability, performance, confidentiality, resiliency, and flexibility. Note that if you visit Hyperledger’s documentation, you’ll often see the term distributed ledger technology (DLT); this term is synonymous with blockchain. Chapter 8 Hyperledger Hyperledger Overview The modular architecture allows you to adjust things like the blockchain’s consensus mechanism, as well as manage storage, set services for identities, set permissions for the identities you set, and create smart contracts (in Hyperledger Fabric, smart contracts are called chaincode). In terms of programming languages, Hyperledger’s chaincode is written in Go (Golang); however, you can utilize JavaScript with the Hyperledger Composer tool. Chaincode can then be used to implement and automate the business logic. The Hyperledger project’s managing team consists of ten members, and the executive director at the time of writing is Brian Behlendorf. In addition, 159 engineers from 27 organizations contributed to Hyperledger Fabric v1.0, according to “Hyperledger is an open source development project to benefit an ecosystem of Hyperledger based solution providers and users. It is focused on blockchain related use cases that will work under a variety of industrial sectors.” —Brian Behlendorf (executive director, Hyperledger) Hyperledger is hosted by the Linux Foundation, and in terms of adoption, it’s supported by large enterprise companies such as IBM, Intel, and SAP, as well as implemented by Oracle, Accenture, The National Association of Realtors, Deutsche Borse Group, Sony Global Education, and many others. The Hyperledger consensus mechanism allows the network of nodes to choose between a no-op (no consensus) mechanism and an agreement protocol called Practical Byzantine Fault Tolerance (PBFT). The PBFT consensus enables two or more nodes to agree by giving the nodes full control. This precludes other nodes on the network from forcing a block, which can prevent potential double spending attacks, as you saw with PoW’s 51 percent potential for mining attacks. Hyperledger gives 300 Chapter 8 Hyperledger control over the consensus mechanism, and you can restrict access to transactions. This results in improved performance and scalability as there are fewer nodes that need to agree on a block. Additionally, PBFT provides privacy for the network, which fits businesses better instead of providing full transparency as you have seen in other blockchains. To give you an idea about Hyperledger’s flexibility, you can use a dynamic consensus and enable what is called hot swapping, where you replace the consensus algorithms while the network is running (done with Hyperledger Sawtooth). Blockchains focused on cryptocurrency usually provide transparency of transactions and network data, because they are dealing with funds and mostly untrusted members. However, this also limits the flexibility and how much you can modify the network and how much you can control as you are limited by the set of rules. Hyperledger is not backed by its own currency and provides more granular control. Hyperledger project was built with basic functionality, vanilla flavor, with the intention of enabling developers to customize as much as possible, from the blockchain’s consensus mechanism to the web interface identity’s permissions, which provides limited data to members. This modular architecture approach allows developers to create specific customized personalized blockchains to fit exact business needs. Hyperledger contains the following main open source frameworks and tools. – Hyperledger frameworks: • Hyperledger Fabric (contributed by IBM): This is a permission blockchain infrastructure with SDKs for Node.js, Java, and GoLang. Hyperledger Fabric is the heart of Hyperledger and supports chaincode in GoLang and JavaScript (utilizing Hyperledger Composer or natively). Blockchain is based on the endorser/orderer architecture. You’ll learn more about this later this chapter. 301 Chapter 8 Hyperledger • Hyperledger Burrow: This is an Ethereum VM built to specification. • Hyperledger Indy: Think independent. This is a tool and library for running independent identities on distributed ledgers. • Hyperledger Iroha: This is focused on mobile applications; the code is based on Hyperledger Fabric. • Hyperledger Grid: This is a solution for a supply chain on a distributed ledger. The framework encapsulates Hyperledger implementations of data types, models, and smart contracts as well as showcases practical ways to create a supply chain business solution. • Hyperledger Sawtooth (contributed by Intel): This framework includes dynamic consensus and enables hot swapping of consensus algorithms on a running network. This is a more traditional blockchain architecture. – Hyperledger tools: 302 • Hyperledger Caliper: This is a blockchain benchmark tool. • Hyperledger Cello: This is an on-demand blockchain module toolkit for creating, managing, and terminating blockchains. • Hyperledger Composer: This tool has collaboration features used with Hyperledger Fabric for building blockchains aimed at businesses for chaincode and blockchain applications. Chapter 8 Hyperledger • Hyperledger Explorer: This is a module to view, invoke, deploy, and query blocks, transactions, and network data. • Hyperledger URSA: This is a shared cryptographic library; it includes shared projects such as the implementation of several different signature schemes (base crypto libraries) and Z-mix, zero-knowledge proofs ( hyperledger-labs/z-­mix). • Hyperledger Quilt/Interledger.js: This is an Interledger Protocol (ILP), meaning an atomic swapping between ledgers. The payments protocol enables transferring an asset (value) across distributed and nondistributed ledgers. There are two implementations: the Java one is called Quilt, and the JavaScript one is called Interledger.js. A Hyperledger project can be built to allows transactions to be transparent as well as confidential when needed. For instance, think of the following business need: an airline wants to sell seats to another business, let’s say Expedia. The airline business need is to create its own blockchain to keep track of its inventory, create transactions, set the price, and keep data confidential. The airline can benefit from blockchain, but it has no need for cryptocurrency nor does it want to share all the data publicly. The airline can utilize Hyperledger and set a private permission network, without exposing the data to the whole world, as you would on a public ledger. The airline can then set special permissions to identities by issuing encryption keys with limited access and then give these encryption keys to specific parties only. For instance, only one organization, let’s say Expedia, is able to view Expedia-related transactions, seat pricing, and 303 Chapter 8 Hyperledger flight information, while other identities such as the actual customer can view only the reservation’s information related to their account and flight information. The finance team can hold the encryption key that can provide more data such as profits and loss, cost of fuel, and other data needed for internal usage. This can be beneficial to businesses because they can run their data on a ledger instead of a centralized database, which is more prone to hacker attacks. As you see, Hyperledger is a large project that covers six frameworks as well as five tools. It is impractical to cover all these in one chapter; in fact, it could easily take a whole book. In this chapter, I will give you a good foundation that can help you understand Hyperledger basics, and you can continue to experiment on your own with the other platforms and tools. In this chapter, you will be focusing on Hyperledger Fabric, as it’s the most popular Hyperledger platform. Understanding Hyperledger Fabric As I pointed out, Hyperledger Fabric is an open source framework implementation, and it’s intended for a private and permission-based business network. In this chapter, you will create private network permission identities, and then you will create a chaincode to implement specific business logic. Hyperledger Fabric is designed as the foundation for Hyperledger, and you can then use the Hyperledger’s modular architecture to add specific modules depending on your business needs. A Hyperledger Fabric network consists of the following components: – Assets: Assets are key-value pairs that represent a value. A value can be anything such as a document, stock, or cryptocurrency token. Each asset holds a state and ownership. 304 Chapter 8 Hyperledger – Shared ledger: A shared ledger holds its own copy of the ledger with the state of the asset. This ledger is called the world state. The shared ledger also holds a copy of the blockchain, which stores the ownership of the asset by recording the transaction’s history. – Smart contracts (chaincode): Hyperledger Fabric calls smart contracts chaincodes that can be programmed in Go (GoLang) or JavaScript (Node.js). Chaincode can interact with the shared ledger, assets, and transactions. There’s nothing new here; you saw this in other blockchains. Chaincode contains the business logic and can set an endorsement policy. Note  In Hyperledger Fabric, users can define an asset endorsement policy for the execution of a chaincode. The endorsement policies set the node peers that are needed in order to agree on an accepted transaction to be valid and added to the shared ledger. – Membership services provider (MSP): The MSP is the certificate authority that manages the digital certificate; it manages user IDs and authenticates all participants on the network. All members must be known identities in order to transact on Fabric. That’s because the network is private and based on permissions. The MSP is used to authenticate and validate these members’ identities and permissions. The MSP uses a certificate generation tool called cryptogen. To understand MSP better, visit the documentation here: https://hyperledger-fabric. 305 Chapter 8 Hyperledger – Peer nodes: The Hyperledger Fabric network is built on peer nodes that are owned and contributed by members of the network. A node can be an organization or an individual. Nodes hold shared ledgers and can execute chaincode. Nodes can access ledger data; they can endorse transactions and interface with applications. Nodes can have ­permission to endorse peers or role for endorsers. Peer nodes receive ordered ledger state updates as part of the blocks they receive in order to maintain the ledger, or what Hyperledger calls world state. – Channel: Channels can be created by a collection of peer nodes. A group of nodes can create a separate ledger of transactions. A channel is similar to the P2P channel you created when you formed your own blockchain in Chapter 3. – Organizations: Each peer node contributes resources, and together they form the collective network. The owning organization can assign peer nodes using a digital certificate through the MSP. Additionally, peer nodes from different organizations can join a channel. Organizations with separate peer nodes are able to share the same MSPs. Best practice is to have one MSP for each organization. – Ordering service: This service packages transactions into blocks. Blocks can then be broadcast to peer nodes and clients on the shared P2P channel. The channel outputs the same messages with the same logical order to all peer nodes. A consistent logical order is called atomic delivery. Take a look at Figure 8-1, which is a graphical representation of the components that make up Hyperledger Fabric. 306 Chapter 8 Hyperledger Figure 8-1.  Hyperledger Fabric graphical explanation. Photo credit: Let’s walk through the Fabric network using the 10,000-foot graphical overview in Figure 8-1. The Hyperledger Fabric network acts as the back-­ end layer for client applications. A client application can be anything such as a dapp, portal, business activity, or web site; these types of applications are the front-end layer, and they can access chaincodes, transactions, and events through coding the Hyperledger Fabric SDK or a REST web service. The client calls a chaincode node, which uses the SDK to interact with the network. Unlike the traditional blockchains covered so far, Fabric is different because not all peer nodes have the same permissions. Also unlike traditional blockchains, Hyperledger Fabric does not allow unknown identities to transact on the network. Organizations, which are called members, build the Hyperledger Fabric network, and each member can set up their node peers through the MSP. You can see in Figure 8-1 that the example has ORG1 MSP and ORG 2 MSP. Peer nodes can be set up with different rules in the network: endorser peer, anchor peer, and orderer peer. – Endorser peer: This receives a request to validate the transaction and execute chaincode. The endorser can approve or disapprove the transaction. Only the endorsing peer executes chaincode, so there’s no need to install chaincode on all peer nodes. 307 Chapter 8 Hyperledger – Anchor peer: These peers receive messages and send messages to other peers in the organization. The P2P network is made up of the different channels that can be set up with permissions so they are not visible to everyone on the network. – Orderer peer: This peer handles the shared ledger and is responsible for keeping state across the network. The orderer peer generates blocks and broadcasts to all peers. The orderer peer can be set as Solo or Kafka. Solo: This is used for development with a single point of failure. That’s what you’ll set for your development environment in this chapter. Kafka: This is used for production. Kafka is built with fault-tolerant features. You’ll create chaincode and deploy it to the Fabric network on a Solo peer, and then you will be able to access and run functions. To send a transaction, your client application can connect to the SDK and create a transaction. The transaction is then sent to the endorsing Solo peer, which verifies the signature and sends an endorsement signature. The endorsement signature is sent out to the ordering service. In production, the ordering service will then send the transactions to all network-­ connected peers, which update their world state on their ledger. I encourage you to visit the Hyperledger page to learn more and read the white papers: Installing Hyperledger Fabric and Composer A good place to start with a Hyperledger network is to install Hyperledger Fabric and Composer. You will be setting up the environment by installing all the tools and libraries as well as Hyperledger Fabric and 308 Chapter 8 Hyperledger Composer; then you will verify installation went well by starting and stopping Hyperledger Fabric and checking that Composer’s libraries installed correctly. P rerequisites Hyperledger Fabric and Hyperledger Composer rely on many tools and libraries, and because each user uses a different machine, it is possible that this process won’t be quick and easy and will probably limit the adaptation of the Hyperledger. I have broken the process down to these steps: 1) Verify the already installed prerequisites. 2) Update Git. 3) Install Node Version Manager. 4) Update Node.js. 5) Install VSCode. 6) Install Hyperledger Composer Extension. 7) Install the Hyperledger Composer Essential CLI tools. 8) Install Hyperledger Fabric. It’s recommended that you visit the Hyperledger Fabric prerequisites page as the versions and requirements may have changed: https://­ prereqs.html. Before getting started, it’s recommended that you update and upgrade Brew if you haven’t done so for a while. > brew update && brew upgrade 309 Chapter 8 Hyperledger Verifying the Already Installed Prerequisites There is a long list of prerequisites for installing Hyperledger Fabric; however, if you have been following along with this book’s chapters, most of the prerequisites should already be installed on your computer. For the operating system (OS), Fabric needs at least macOS 10.12. You can check your version via the top-left menu on your computer. Click the Apple icon, and click About This Mac. The Overview tab opens and shows the macOS version. If you are running an older version, then get the 10.12 update by clicking the software Update button. At the time of writing, macOS is called Mojave at version 10.14.4. You also need Xcode and Docker. These were already installed in previous chapters, but you need to confirm they are installed and are the correct versions. Just run the xcode-select -version command to ensure Xcode is running. You can compare your results with mine, shown here: > xcode-select -v xcode-select version 2354. > docker -version Docker version 19.03.0-beta3, build c55e026 You need Docker-Compose version 1.8 or higher. > docker-compose -version docker-compose version 1.24.0, build 0aa59064 You need npm version v5.x or higher. > npm -version 6.8.0 You need Python 2.7.x or higher. > python -version Python 2.7.10 310 Chapter 8 Hyperledger Updating Git The installation is requesting Git 2.2.x or higher. However, Mac comes with an older version of Git; you can check your version with this: > git -version git version 2.20.1 (Apple Git-117) To upgrade Git, you will be installing Git via Brew and set your machine to use the Git version in Brew instead of the one that comes with Mac. First, install Git via Brew. > brew install git Next, you will set your path to point to the new Git location; use vim or your favorite text editor. > vim ~/.bash_profile Add the following to the PATH: #git point to brew PATH=/usr/local/bin:$PATH Don’t forget to run bash_profile after you save and quit the bash profile file to ensure the changes take effect. > . ~/.bash_profile Lastly, you can verify the version of Git. > git -version You are now pointing to the location of Git you installed with Brew, and for a future upgrade of Git, you can just run the following: > brew upgrade git git version 2.21.0 311 Chapter 8 Hyperledger Installing Node Version Manager (nvm) Node Version Manager (nvm) is needed. To download or update nvm, check the GitHub page at and run this command: > curl -o- v0.33.0/ | bash Once the installation is completed, you can confirm it’s installed correctly. Open a new terminal, and type the following. I have version 0.34.0 installed. > nvm -version 0.34.0 U pdating Node.js Node needs to be version 8. To check what you are running, run this command: > node -version At the time of writing, the prerequisites page stated that you should install the latest (long-term support) version of Node; however, it has been generating fatal errors and has a recorded bug on GitHub. Node.js version 9 is not supported either at the time of writing. To get Hyperledger Composer to work, you will be installing node 8 and pointing nvm to use node 8. > nvm install 8 > npm config delete prefix > nvm use 8 You can confirm node 8 is installed and set correctly. > node -version v8.15.0 312 Chapter 8 Hyperledger Installing VSCode with Hyperledger Composer Extension It’s recommended that you install Visual Studio Code (VSCode) with the Hyperledger Composer extension and use it as your code editor. The extension will provide code highlighting and is a professional free IDE. To get started, download VSCode from here: https://code.visualstudio. com. Click Download for Mac, as shown in Figure 8-2. Figure 8-2.  Visual Studio Code installation page Once installation is complete, launch VSCode. To install the Hyperledger Composer extension, click VSCode’s left menu, select Extensions (two square icons) from the left menu bar, and type Hyperledger Composer in the search box. Select: Hyperledger Composer. Then click Install. Lastly, Reload to activate it. See Figure 8-3. 313 Chapter 8 Hyperledger Figure 8-3.  VSCode Hyperledger Composer extension Hyperledger Composer Essential CLI Tools You will be installing the Hyperledger Composer Essential CLI tools including composer-rest-server, Composer Playground, and the Yeoman generator. To install the Composer CLI, run the following command. > npm install -g composer-cli @0.19 Note  I am using version 0.19. There are some open bugs with Hyperledger’s latest version, 0.20.6, in connection with all the tools and libraries, so I am using a previous version of Hyperledger Composer and Hyperledger Fabric. This may change, so you may want to check the documentation and install another version. Also, I assembled many potential bugs you may run into during installing and running Hyperledger Composer and Fabric; see the “Error Troubleshooting” section later in this chapter. 314 Chapter 8 Hyperledger Next, install the Yeoman tool for generating Hyperledger Composer applications, which utilizes generator-hyperledger-composer. Execute the following command: > npm install -g [email protected] You can now install Composer Playground globally with npm. > npm install -g [email protected] Part of Composer is a tool called composer-rest-server that generates a loopback-based REST interface to be able to access the network you will create. To install the tool, execute this command: > npm install -g [email protected] > npm install -g Yeoman You can verify that the installation went well by running the -version flag. > composer -version v0.19.20 > composer-rest-server -version v0.15.2 > composer-playground -version 0.20.6 To ensure the generator tool was installed, if you run the Yeoman command, it should list Hyperledger Composer generator. > Yeoman It will output the following: ? ‘Allo! What would you like to do? (Use arrow keys) Run a generator ◻ Hyperledger Composer Press Control+C to get out of the Yeoman command. 315 Chapter 8 Hyperledger Installing Composer Playground with Docker In addition to installing Composer tools globally with npm, you can run Hyperledger Composer Playground with Docker; just run the container and assign composer-playground as the name. You will be running it on port 8080. > docker run -name composer-playground -publish 8080:8080 hyperledger/composer-playground The Docker command downloads the image, and you can see the output in Figure 8-4. Figure 8-4.  Composer-playground docker container output To cancel the container, press Control+C. Now to run Playground in the browser on port 8080, open a new Terminal window by pressing Command+T and run the open command. > open http://localhost:8080 You can see the Hyperledger Composer playground welcome page, as shown in Figure 8-5. 316 Chapter 8 Hyperledger Figure 8-5.  Playground welcome screen Keep in mind that to stop Docker, you can run the stop command. > docker stop composer-playground To remove the composer-playground name so you can use it again, you will need to run the following command: > docker rm -force composer-playground Installing Hyperledger Fabric Dev Servers At the time of writing, Hyperledger Fabric’s latest version is v1.4.1; you should visit the GitHub page to find out the latest version and documentation as this may change; see hyperledger/fabric. 317 Chapter 8 Hyperledger The Hyperledger Fabric dev servers have different versions to choose from. You will be setting up a Hyperledger Fabric v1.2 network for your development. You then can deploy your blockchain business networks built with Hyperledger Composer and test your applications. Create a directory to download Fabric; I picked ~/fabric-dev-­ servers, but you can choose any directory. > mkdir ~/fabric-dev-servers && cd ~/fabric-dev-servers You’ll use curl to get the .tar.gz file you need to install Hyperledger Fabric, as shown here: > curl -O composer-tools/master/packages/fabric-dev-servers/fabric-dev-­ servers.tar.gz Use tar to extract the files you downloaded. > tar xzf fabric-dev-servers.tar.gz Once these are extracted, you have script files to help you quickly spin up a Hyperledger Fabric instance. Run the ls command, and you can see the .sh files among other useful files. > ls 318 Chapter 8 Hyperledger When you run the Composer -v command, you can check the version you are running. You saw that you indeed installed Hyperledger Composer v0.19, so you will need to use Hyperledger Fabric v1.1 according to the documentation, and you can also set the starting Fabric timeout to 30 seconds; that’s the wait time once you run the script to ensure the network is running. > export FABRIC_VERSION=hlfv11 > export FABRIC_START_TIMEOUT=30 Tip  If you are running a different version of Hyperledger Composer, check the GitHub page to see which version of Fabric you need to set: master/packages/fabric-dev-servers. To spin up your Hyperledger Fabric network, you need to first execute the download Fabric script; this can take some time, depending on your Internet connection. >./ That’s it; you should see the output shown in Figure 8-6. 319 Chapter 8 Hyperledger Figure 8-6.  Downloading the Hyperledger Fabric output Once the download is complete, you can confirm you have Docker containers. > docker image ls hyperledger/* hyperledger/fabric-ca hyperledger/fabric-orderer hyperledger/fabric-peer hyperledger/fabric-ccenv hyperledger/fabric-couchdb Network Connection Profile There is a network connection profile JSON file called DevServer_ connection.json. 320 Chapter 8 Hyperledger In this section, you will modify the file to fit with the Docker localhost container you will create. Before you modify the file, it’s a good idea to make a copy first. > cd ~/fabric-tools/ > cp DevServer_connection.json DevServer_connection-backup.json Change the original file’s orderers, peers, and certificate authorities to point to localhost as you will be running Composer Rest Server as the Docker container in the network and will access these hostnames on the network. Edit the DevServer_connection file with vm or your favorite editor. > vim DevServer_connection.json See Figure 8-7. Figure 8-7.  Changing devServer.json to point to localhost You also need to edit the hosts to point to on the local server. > sudo vim /etc/hosts # fabric 321 Chapter 8 Hyperledger pinning Off a Local Hyperledger Fabric S Business Network The first time you run Hyperledger Fabric, you need to execute commands to start a local Hyperledger Fabric instance and issue an ID card for the admin. The default admin is called PeerAdmin. To get started, run the start fabric command. > ./ The expected output is confirming your variables. Development only script for Hyperledger Fabric control Running ‘’ FABRIC_VERSION is set to [version number] … Creating network “composer_default” with the default driver Creating Creating As part of the start script, you can see the output lines that confirm that the composer_default Docker network was created and running the containers in the created network. The containers are able to communicate using the custom hostnames: and Creating an Admin ID Card Now that you have a network running, the last setup step is to create credentials. You can use Hyperledger Composer to create what Hyperledger Fabric calls a .card file. 322 Chapter 8 Hyperledger You can generate the admin ID card by executing the following command: > ./ You can compare your output with mine, which is shown in Figure 8-8. Figure 8-8.  Hyperledger Composer generate card To confirm the card was created correctly, execute the following command with : > composer card list -card [email protected] This command outputs information about the ID card. See Figure 8-9. 323 Chapter 8 Hyperledger Figure 8-9.  Hyperledger Composer card list Stopping Hyperledger Fabric Leave Fabric running for now, but once you complete your exercises, you can shut down the Hyperledger Fabric runtime by executing the stop command. > ./ Also, you should execute the teardown script at the completion of your development cycle to ensure the memory is freed. > ./ Note  If you run the teardown script, the next time you start the runtime, you’ll need to create a new PeerAdmin card just like you did with the first-time startup steps. See the following steps. Re-creating the PeerAdmin ID Card After you stop and tear down with these commands: > ./ > ./ 324 Chapter 8 Hyperledger you need to re-create the admin ID card, so just follow the same commands. > ./ > ./ > composer card list -card [email protected] It’s a good idea to follow the process in Figure 8-10, which shows what you need to do in order to start a card, stop a card, create a card, and tear down. Figure 8-10.  Fabric-dev-servers start-stop flow. Photo credit: github. com/hyperledger/composer-tools. H yperledger Composer Now that you have the Hyperledger Fabric network installed and running, the next step is to write chaincode. You can write chaincode in Hyperledger Fabric natively with Go; however, you can also utilize Hyperledger Composer to help create chaincode and blockchain applications via coding in JavaScript instead of Go. Hyperledger Composer takes definition files and generates Business Network Archive (.bna) files that you can then deploy to the Hyperledger network to run. Composer is easy to use and aimed not just at developers but at business owners. 325 Chapter 8 Hyperledger There are three components that make up Hyperledger Composer (see Figure 8-11). • Business network archive (.bna): This consists of four files packaged together. • Hyperledger Composer Playground: This is used to configure and deploy network as well as test code without rolling out a blockchain. • REST API support: This exposes functions to be used by front-end clients such as dapps. Figure 8-11.  Hyperledger Composer graphical explanation. Photo credit: “Hello, World” with Playground You will be creating a “Hello, World” application and deploying it on the network using Playground. To get started, open Playground via the command line and execute this command: > composer-playground 326 Chapter 8 Hyperledger Alternatively, you can use Docker. Once it’s open, dismiss the welcome screen by clicking “Let’s Blockchain!” Deploying a Business Network Next, select “Deploy a new business network.” In the deploy wizard, insert the basic information, such as typing hello-network in the “Give your new Business Network a name” input box. Select the middle “empty-business-network” network definition and click Deploy, as shown in Figure 8-12. Figure 8-12.  Hyperledger Composer Playground, deploying new business network wizard The ID card for an admin is created for your network. To connect to the network, click the “Connect now” link, as shown in Figure 8-13. 327 Chapter 8 Hyperledger Figure 8-13.  Connecting to the hello-network business network definition You are now connected to the business network definition network, and you can define and work with the model. Business Network Archive (.bna) The business network model includes assets and the transactions related to these assets. Hyperledger Composer needs the following to be packaged together: a network model file, a JavaScript file (.js), an access control file (.acl), and a query file (.qry). These files are definition files that generate your network. – Network model (.cto): This is the file that defines the assets, transactions, and participants who can interact with these assets. The file is created with a modeling language called CTO (named after the original project name, Concerto). 328 Chapter 8 Hyperledger – JavaScript file (.js): This is the file that defines the transaction processor functions. It is the chaincode. – Access control (ACL) (.acl): This is the file that contains the access control rules that define the rights of the different participants. – Query (.qry): This is the file that defines the queries that can run in a network. Hyperledger Composer takes these four files and creates a business network definition that is packaged as an archive (.bna) file. The .bna files can be deployed on the Hyperledger Fabric network. You can than write a client application such as a dapp that can use Hyperledger Composer APIs to access the smart contract (.bna functions) that you write through the Hyperledger Fabric network. Adding the Model File To create the model file, you can add the files that make up the .bna archive. For instance, to add a model file. Click “Add a file,” select Model File (.cto), and click Add, as shown in Figure 8-14. 329 Chapter 8 Hyperledger Figure 8-14.  Adding a file to the business network model For the .cto file, you will define the processing function and transaction. For the namespace, you will use a fictional company called Skynet, with an identified ID of type String. You will also create a msg string and a transaction Hello and pass the Myfunction asset that will include the message. namespace org.skynet.mymodel asset Myfunction identified by id { o String id o String msg } transaction Hello { -> Myfunction check } 330 Chapter 8 Hyperledger A dding Chaincode Next, you will add a JS file by clicking “Add a file.” Write chaincode as the logic of the transaction to print the message to the console, as shown here: /** @param {org.skynet.mymodel.Hello} hello @transaction */ function hello(hello) { console.log(“Hello ” + hello.check.msg); } Transactions represent the chaincode, which is the business logic of your application. Notice that the comments state that the code is a function for a transaction and the namespace. Click “Deploy changes” to update your definition model. C reating an Asset Next, to test the model, you will create a new asset, extend it, and store it. To do that, click + Create New Asset at the top-right corner. The create new asset wizard opens, as shown in Figure 8-15. The model already has an ID; however, for this example, you will change it to 001 (but the string can be any string). For the message, you will pass world. 331 Chapter 8 Hyperledger Figure 8-15.  Create New Asset Wizard A ccess Control Notice that there is an Access Control option with the permissions.acl file as part of the Define tab at the bottom left of the screen, as shown in Figure 8-16. As you can see, the rules grant wide-open “allow all” access, which can be changed. 332 Chapter 8 Hyperledger Figure 8-16.  ACL permission file on your hello-network T esting the Model Now that the model instance is saved, you can submit the transaction to invoke the transaction. On the left side, click the “Submit transaction” button. The Submit Transaction Wizard opens. Set the ID to 001, as shown in Figure 8-17. Figure 8-17.  Hyperledger Playground, Submit Transaction Wizard 333 Chapter 8 Hyperledger Before you test, open the developer console so you can see the JavaScript messages. For Safari, follow these instructions. In the top menu, select Safari ➤ Preferences. Click the Advanced tab and then select the “Show Develop menu in menu bar” box. After following these steps, you will see in the top menu Developer as an item. Select “Show JavaScript console” (or press Command+Option+C). Next, click Submit; you will see the message “Hello world” in the JavaScript console, as shown in Figure 8-18. Figure 8-18.  “Hello world” message showing in the JavaScript console I mporting/Exporting the Model To export the model, you can generate the business network archive (.bna) file. The .bna file can then be deployed in production. All you have to do is click the Export link, as shown in Figure 8-19. 334 Chapter 8 Hyperledger Figure 8-19.  Exporting the .bna file Playground generates the hello-network.bna file, which will be downloaded to your computer. Similarly, you can import a .bna file, click the “Add a file” link, and under “Upload a file from your computer…,” you can browse or drag and drop the .bna file. The import/export is not just for publishing; it can be used to share models with others for testing, development, or other reasons. I included the hello-network.bna file with this book’s code, so feel free to import it; see hello-network. The .bna file is nothing more than a zip folder named bna. In fact, you can copy the .bna file as .zip and unzip the files. > cp hello-network.bna > unzip VSCode can be used as your IDE for your entire Hyperledger project. For instance, now that you have unzipped your files, you can open VSCode and drag and drop the model file models/org.example.model.cto into VSCode. You can see that the code is highlighted, as shown in Figure 8-20. 335 Chapter 8 Hyperledger Figure 8-20.  Model CTO file in VSCode You wrote your files in Composer Playground using the web interface. This suite is a less developer savvy approach; however, a larger project can include complex business logic, events, many transactions, and testing, so it is advisable to create your project and manage files with VSCode and then upload those files into Playground for deployment. P layground Online Hyperledger Composer Playground has an online version available at You can use the same steps you used before to create your network and files. See Figure 8-21. 336 Chapter 8 Hyperledger Figure 8-21.  Composer Playground To test Playground Online, you can import the hello-network.bna file you created previously. To do so, first click “Let’s Blockchain!” and under “2. MODEL NETWORK STARTER TEMPLATE” select “Drop here to upload or browse” and upload the hello-network.bna file. Click the Deploy button at the bottom-right corner. You can see the network created. Click the “Connect now” link to connect to the new network. See Figure 8-22. 337 Chapter 8 Hyperledger Figure 8-22.  hello-network connect link You can repeat the same steps to create an asset and test, just as you have done on the local playground. Creating a Business Network with Yeoman You used Hyperledger Playground to generate your business network. Hyperledger Playground is aimed not just for developers but also at business owners because of its simplicity; however, you can also create a network in Terminal. Yeoman provides a wizard you can use. If you are unfamiliar with Yeoman, it provides a wizard generator through the command line. You can either run Yeoman and select Hyperledger Composer and the Business Network generator or run the following: > Yeoman hyperledger-composer:businessnetwork Keep in mind that Hyperledger Composer can be used for more than just generating the business network; it can be used for Angular, LoopBack, and Model as well. See Figure 8-23. 338 Chapter 8 Hyperledger Figure 8-23.  Generating hello-network with the Yeoman wizard The hello-network folder is generated and includes permissions.acl, models, features, test, and lib. Next, to create the .bna file, you can use Hyperledger Composer. See Figure 8-24. > cd hello-network > composer archive create -t dir -n . 339 Chapter 8 Hyperledger Figure 8-24.  Generating the hello-network BNA file with Hyperledger Composer Run the ls command and confirm that the [email protected] file is generated. > ls *.bna [email protected] eploying on a Local Hyperledger Fabric D Network To deploy the .bna file to a local Hyperledger Fabric network, run the composer network install command and point to the .bna file while specifying the identity card. > cd ~/fabric-dev-servers/ > composer network install -archiveFile ~/Desktop/hello-­ network.bna -card [email protected] This will result in the successful output shown in Figure 8-25. 340 Chapter 8 Hyperledger Figure 8-25.  Installing local Hyperledger Fabric command output Running the “hello-network” Network Hyperledger Composer is the application development framework for building blockchain applications based on Hyperledger Fabric. Hyperledger Composer generates REST APIs based on the business network definition you created. This is done using what is called a LoopBack connector. You can take these REST APIs to be used by a) a client such as a dapp b) integrate with non-blockchain clients such as a web site. That allows you to use the blockchain ledger just as you would use any other database with a middleware. That is powerful. Hyperledger Composer can generate a REST interface. You can run Hyperledger Fabric on your computer and generate a GUI that you can then use to interact with the network running on your computer just like it would be on a real production server. tarting the “hello-network” Business Network S and Admin Card To run your “hello-network” network, run the following command, and see the output in Figure 8-26: > composer network start -networkName hello-network -networkVersion 0.0.2-deploy.3 -A admin -S adminpw -c [email protected] -file networkadmin.card 341 Chapter 8 Hyperledger Figure 8-26.  Starting the business network To confirm this worked, you can run the docker ps command. You should see the­ deploy.3-0 image created, as shown in Figure 8-27. > docker ps Figure 8-27.  Docker container hello-network Importing a Business Card Next, import a new network admin card so you can use [email protected]­ network in the business network you started. > composer card import -file networkadmin.card This command imports the network admin card, which will include [email protected] > composer network ping -card [email protected] 342 Chapter 8 Hyperledger You can compare your output with mine, which is shown in Figure 8-­28. Figure 8-28.  Importing the business network card W here to Go from Here From here you can choose from many passport strategies for your users. For example, you can use Google OAUTH2.0, SAML, Passport-JWT, or LDAP, depending on what your organization is using. Then you will be able to run a REST server in multiuser mode and test the interaction with a client application such as the one you created. Here are couple of articles that can help you with the process of setting up your app for authenticating multiple users: • Passport-JWT: composer/latest/tutorials/google_oauth2_rest • Google OAUTH2.0: hyperledger/fabric-ca docker hyperledger/fabric-orderer hyperledger/fabric-­ peer hyperledger/fabric-ccenv hyperledger/ fabric-couchdb Hyperledger is a large project, and it consists of five major platforms as well as five major tools. This chapter focused only on Hyperledger Fabric. However, you are encouraged to continue experimenting with other Hyperledger platforms and tools such as Hyperledger Sawtooth, including setting up an environment, creating an account, writing a more complex chaincode, and deploying as well as connecting your chaincode to a dapp. 343 Chapter 8 Hyperledger To get more information on getting started, visit the official web site here: latest/getting_started.html. In fact, you can find more information about all the platforms and tools here: Lastly, bookmark the Hyperledger dev center here: https:// E rror Troubleshooting Hyperledger was built to be plain and allows you to stitch together modules on many different machines, but not without problems. Hyperledger is set up for more advanced users and may request system admin privileges to set up servers. You may have encountered a few errors, so here I have compiled them into this section. omposer Runtime Install Error or Card Not C Found If you get errors such as these: – “composer runtime install error card not found peerAdmin” – “Error: Card not found: [email protected]” it’s because the admin ID card was not created successfully or the correct process wasn’t followed; all you need to do is remove the ID card and re-create it. You need to remove the composer folder, create a new folder, and run the command again. > rm -rf ~/.composer > mkdir ~/.composer > ./ 344 Chapter 8 Hyperledger ocker Unauthorized Authentication Required D Error You may get the following error while downloading Hyperledger Fabric: • “unauthorized: authentication required” There are issues with authenticating or proxying to Docker Hub and not Hyperledger Fabric. To try to fix this, set your computer time to match UTC time zone: Create an account with Docker at, and then log in. > docker login Alternatively, try again after you logged out. > docker logout Docker Container Conflicting Errors When you are using the Docker container for a project, you might need to re-create a container or stop a container; otherwise, you may get conflicting errors. All you need to do is stop and remove the container. > docker stop [container id] > docker rm [container id] 345 Chapter 8 Hyperledger Tip  If you already created a Mongo-Docker container or any other Docker container that creates a conflict, you will get the following conflict error when you try to create a new one: “The container name is already in use by container [container id].” All you need to do is stop the container and remove it. > docker stop [container id] > docker rm [container id] Mismatch and Cleanup If you have a mismatch between Hyperledger Composer and Hyperledger Fabric versions, you may get the following error: • “Starting business network definition. This may take a minute… Error: Error trying to start business network. Error: Failed to connect to any peer event hubs. It is required that at least 1 event hub has been connected to receive the commit event Command failed.” This error is also generated on Hyperledger Fabric 1.2 with Hyperledger Composer 0.20.6 because there is an open bug. To fix this, you need to check your Hyperledger Composer and uninstall through npm, as well as re-install Hyperledger Fabric. Additionally, if you need to completely clean up, you need to stop and tear down Fabric. To remove the Docker images, remove fabric-dev-­ servers, and lastly remove Composer, follow this process: > cd ~/fabric-tools > ./ > ./ 346 Chapter 8 Hyperledger Next, stop the Docker containers, remove them, and also remove all the Docker images by running these commands: > docker kill $(docker ps -q) > docker rm $(docker ps -a -q) -f > docker rmi $(docker images -q) -f You can now completely remove fabric-dev-servers. > rm -rf ~/fabric-dev-servers To remove Composer and admin ID card, run these commands: > sudo rm -rf ~/.composer > npm uninstall -g composer-cli The npm uninstall command will output a confirmation that the library was uninstalled. Summary In this chapter, I introduced Hyperledger to help you get started and understand the power of it. I covered the Hyperledger ecosystem and terminology and gave you a good understanding of the pieces that make up the network as well as the major Hyperledger platforms and tools available. You installed Hyperledger Fabric and Hyperledger Composer, ensuring the prerequisite libraries are installed. You created “Hello, World” application with Playground as well as create a .bna file you deployed on a local network. I mentioned Hyperledger Playground Online as well as explained how to generate a network with Yeoman generator. I covered the different pieces that make up the .bna archive file including handling ID cards. I also covered potential errors and troubleshooting to ensure your installation went well. Lastly, I covered a few recommendations on where to go from here to continue with Hyperledger. 347 Chapter 8 Hyperledger In the next chapter, you will learn how to build a dapp with Angular. Dapps can interact with the smart contracts you have developed in the past three chapters and are an important ingredient in the blockchain ecosystem. 348 Build Dapps with Angular: Part I In previous chapters, I covered different blockchains, and you learned how to create smart contracts that can interact with a blockchain. You created smart contracts in Ethereum, NEO, EOS, and Hyperledger. In Chapter 1, I broke down the process into five layers: consensus layer, miner or booking layer, propagation layer, semantic layer, and application layer. Smart contracts are part of the application layer in the development cycle; however, the application layer is incomplete without having a front-end interface that enables an end user to interact with the blockchain. Tip  Many times you will hear decentralized applications (dapps) referred to as smart contracts. Smart contracts are self-executing contracts. Dapps use smart contracts but run on a P2P network and not on a single system. Developers and more savvy users can interact with the smart contracts you created via the command-line interface and tools mentioned in previous chapters, but developing a front-end application that is able to interact with a blockchain is essential for all other users. You do this by creating a decentralized application (dapp). In this chapter and the next, Chapter 9 Build Dapps with Angular: Part I you will be creating a decentralized application with the help of Angular so that users can interact with a smart contract using a friendly and intuitive user interface (UI). I broke down the process into two parts. Part I, covered in this chapter, contains the following topics: • Developing the dapp, including its benefits and classification • Using Angular, including its architecture, benefits, prerequisites, and creating an Angular skeleton app • Creating and styling Angular custom components Part II, covered in Chapter 10, contains the following topics: • Creating the dapp’s smart contract with Truffle • Integrating the smart contract with the dapp • Linking and connecting your dapp to the Ethereum network Let’s get started. What Is a Dapp? A decentralized application (shortened as ÐApp, dapp, Dapp, dApp, or DApp and pronounced as “dee-app”) is a web application that is able to interact with a smart contract. Dapps run on the blockchain and utilize the distributed ledger. The Ethereum blockchain is currently the most popular platform to run dapps; however, other distributed ledger technologies (DLTs) you have seen also provide the ability to create dapps. I covered NEO, EOS, and Hyperledger in previous chapters; others include ICON, Cardano, and Hashgraph (Hedera). 350 Chapter 9 Build Dapps with Angular: Part I “Everything that can be decentralized will be decentralized.” —David Johnston, CEO of the DApp Fund DecentralizedApplications If you have ever developed a standard desktop, web, or mobile application, you will find that dapps are similar but also very different. A dapp is built using the same tools and languages you use to build any other app, but for an app to be categorized as a dapp, it needs to meet the following criteria: – Open source: Its code is published as open source and should not be governed by one entity (centralized). Keep in mind that the application may adapt its own protocol in response to proposed improvements and market feedback; however, the consensus of its users drives all changes. – Decentralized: Dapps utilize a blockchain or a P2P network. – Incentive: Dapps use digital assets for funding. – Algorithm/protocol: Dapps often generate tokens and include a consensus mechanism such as PoW, PoS, or even their own. These criteria ensure dapps don’t have downtime like other apps you download from marketplaces such as iTunes or Google Play; dapps also give control to a community instead of one entity. These criteria can be significant. For instance, Apple and Google often reject apps for not meeting their arbitrary or monetary-based policies. These policies do not always make sense and are not always in the best interest of the end user; they often are there to block usage of a competitor or for monetary gain. 351 Chapter 9 Build Dapps with Angular: Part I Dapps that are based on open source code implemented on decentralized blockchains and funded by tokens generated using a specific consensus mechanism are believed by many to be the future of all businesses. Only time will tell. Additionally, open source software is an advantage because it allows users to view the source code and potentially contribute. Decentralizing using a blockchain harnesses the advantages of blockchain as DLT and serves as a replacement to the traditional one-server database. Finally, adding records/transactions to ledgers is usually done utilizing tokens, and the consensus mechanism of a token is also an agreement between all the users of the dapp. Dapp Classification In addition to the previous criteria, dapps can be categorized. The classification is based on the infrastructure the dapp is utilizing and can be broken down to these three categories: – Dedicated blockchain dapps: These are dapps that use a dedicated blockchain directly; examples are bitcoin, Ethereum, EOS, and NEO. – Dapps relying on another blockchain: For instance, the Omni Layer Protocol (formerly called Mastercoin) is a digital currency and communications protocol that is built on top of the bitcoin blockchain. – Dapps relying on another protocol that built on top of another blockchain: These dapps use a protocol that is built on top of another blockchain. An example is the safe network using the Omni Layer Protocol. 352 Chapter 9 Build Dapps with Angular: Part I A good example to help understand the classification concept is the USDT (Tether) token. This token was issued twice based on two blockchains: bitcoin and Ethereum. In this case, there are two types of USDT. The original, which is based on bitcoin, is done by using the Omni Layer Protocol to generate the token, and the Ethereum-based USDT is compatible with the Ethereum’s ERC20 standard. Take a look at Figure 9-1. Figure 9-1.  Representation of clasisification for USDT D app Projects Most dapps are built directly on top of the Ethereum blockchain or use a blockchain for their tokens. However, there are some dapps that even build their own dedicated blockchain. Take a look at Table 9-1 for a sample of different dapps and their classifications. 353 Chapter 9 Build Dapps with Angular: Part I Table 9-1.  Example of Dapps and Classifications Dapp Description Ethlance Marketplace for Uses Ethereum directly job postings and hiring freelancers. 0 percent fees. Golem Global market for Token based on Ethereum GNT idle computer power. The SAFE Data storage and Network communications network. Classification Token Blockchain No token Ethereum blockchain Implementation relying SFE on another protocol (Omni protocol) that is built on top of another blockchain (bitcoin) Ethereum blockchain Bitcoin In addition to the information in Table 9-1, there are many resources to find more dapps; these two web sites provide a list of dapps that you can check: and How Do You Create Your Own Dapp? The success of bitcoin and blockchain have brought an explosion of dapps. Developers and business owners have created a basic process to follow for developing dapps. You don’t need to follow this exactly, and it may change by the time of writing; however, many of the published dapps out there have followed this process. The process consists of these five steps: 1. Write a white paper. 2. Launch an initial coin offering (ICO). 3. Develop the dapp. 354 Chapter 9 Build Dapps with Angular: Part I 4. Launch your dapp. 5. Market your dapp. Let’s review these steps. Write a White Paper The white paper is similar to a company’s business plan aimed at investors. However, it targets more than just investors; it’s the technical blueprint. The white paper is the technical document as well as the business plan and should explain the problem being solved and the concept, features, and technical aspects of the dapp. Just like in a business plan, it’s a good idea to include your unique selling proposition (USP), road map, members’ résumés, capabilities, and history to help establish credibility. Note The unique selling proposition (USP) is the problem your dapp is aiming to solve. Once the white paper is published, it is good to get feedback from peers and the community in the early stages and prior to development. Social media, forms, and publications are often used to promote dapps and help create credibility. Launch an Initial Coin Offering Once the white paper is published, the next step is to launch an ICO and sell coins or tokens to fund and support your dapp. The coin should have a reason for existence, rather than be the same as another coin/token out there, so you should explain how and why your dapp needs its own token or coin. 355 Chapter 9 Build Dapps with Angular: Part I You also need to decide on the type of classification for your dapp, which will determine whether you will need any or all of the following: 1) issue token 2) set usage fees. 3) have a dedicated blockchain. 4) have a mining mechanism 5) set the allocation of fees 6) rewards investors 7) allocate fees to pay for different departments of your business: support, development, marketing, and business. D evelop the Dapp Development should be open source, and GitHub is usually used for repos for the development effort. On every release, it’s a good idea to let investors and others know of a release to build users and a developer community around your project. Many dapps have tried to get funds and delivered no usable products; set yourself apart and avoid potential problems with regulators. (I will cover regulators in Chapter 11.) Launch Your Dapp Launch your dapp and include your release notes, documentation, road map, and maintenance plan. It’s crucial to meet the promised launch date. Market Your Dapp The last step is marketing. In addition to traditional marketing, dapps often hire or work with prompters during early phases or after release to get the word out. Another unique marketing aspect for a dapp is to get the coin/ token listed on exchanges. This is the final stamp of recognition. Some exchanges have a voting system put in place to select the next coin/token to be listed. Some exchanges have been abusing this process and charging hefty fees to list a token or coin. For instance, a utility token listing on Binance exchange can cost from $0.5 million to $3 million. Many early investors including dapp owners have been able to “cash out” if a token is listed on major exchanges as its price often goes up high 356 Chapter 9 Build Dapps with Angular: Part I because of the listing; however, it has become more and more difficult for a dapp to be listed, and it needs to provide real value. Fraudsters are often exposed, and coins/tokens get de-listed as quickly as they are listed. Why Angular? With dapps, just like with any traditional app, you can write your application natively to the device you publish your app to (in the supported language of your device such as Xcode for iOS); however, it has been proven that using a framework can speed up development. For instance, if you want to utilize the same code and deploy your application on multiple devices with different screen sizes, that can become a challenge for a small team. Angular helps you build cross-platform modern applications for web, mobile, and desktop at the same time. The Angular CLI and Component Dev Kit (CDK) can help accelerate the development of apps. Using Angular can be beneficial because of the following factors: – Large community support – Enterprise architecture and scaling – Cross-platform support – Documentation Angular is a structural framework and enables you to create front-end client-side applications. The pieces are loosely coupled and structured in a modular fashion, resulting in less code to write, added flexibility, easier-to-­ read code, and quicker development time. Angular allows the developer to put together a toolset for building a framework that will fit your exact application’s needs. You can use HTML as your template language and extend HTML’s syntax so the application’s components can be read easily. Other than HTML, the coding is done with TypeScript, which turns JavaScript into an object-oriented programming language and gives you an enterprise-level environment. 357 Chapter 9 Build Dapps with Angular: Part I Additionally, Angular is well structured and built to be fully accessible, in accordance with accessible rich Internet applications (ARIAs), so your app or site can be built correctly for people with disabilities. Angular also gets along well with other JavaScript libraries so you can install libraries such as the Ethereum JavaScript API web3.js with npm manager. Lastly, Angular’s features can be easily modified or replaced to fit your exact needs. Note The word angular means having multiple angles or measured by an angle. Angular is a structural framework and enables you to create front-end client-side applications for the Web, mobile, and desktop. It is an open source, front-end framework for dynamic app development. Angular’s most significant features are data binding and dependency injection. These can help decrease code. Also, Angular has been around for years; it’s on its seventh release. Note  Dependency injection is a design pattern technique. As the name suggests, it means using one object as a dependency to another object by injecting the code. Angular 2 was a complete rewrite of AngularJS and offered a major change; however, there are no major differences between Angular 2 up to version 8. The latest release version of Angular at the time of writing is 7.3.1, and in this version, a few features were added such as the following: – Dependencies: The dependencies were upgraded, and support for Typescript 3.1, RxJS 6.3, and Node 10 was added. 358 Chapter 9 Build Dapps with Angular: Part I – Bundle budget: You can set a warning for the size of the application to ensure you don’t exceed the limit (the default is 2 MB). – Angular CLI: By running the CLI wizard, you can add components such as routing and decide on the format of the CSS. – Component Dev Kit (CDK) of Angular Material: Add new features such as out-of-the-box virtual scrolling, drag and drop, and “mat-form-field” support for native select fields. (I’ll cover Material later in this chapter.) Angular 8 is at release candidate 2 (rc.2), and the features expected are mostly to improve performance. It will include an improved view engine called Angular Ivy, improved upload of JavaScript for modern browsers that support ES2015+, support for web workers to use hardware for heavy lifting, support for TypeScript, a benchmarks tool, and more. Tip I selected Angular, but Angular is not the only framework that can help expedite development. You can use other frameworks such as React ( and achieve similar benefits. This decision is really a matter of personal taste and your team’s skill set. You could easily convert this project to a React project mostly by copying your project’s files over to the React project. Creating an Angular Dapp In this section, you will be creating an actual dapp that will connect to the Ethereum network and transfer funds from one account to another. This is often the core feature of any dapp out there. For instance, you can build a dapp that sells products, provides services, or pays users to take quizzes, 359 Chapter 9 Build Dapps with Angular: Part I and all these types would need to have a mechanism in place to transfer coins/tokens. In this section of this chapter, you will be creating a dapp utilizing Angular. In terms of environment and deployment, you will be using the Truffle web framework you used in Chapter 5, as it offers benefits for quickly creating a smart contract. Truffle is able to do more than just help compile your smart contract; it does everything you need to inject your smart contract into a web app and can run the test suite. You are also going to utilize MetaMask again to get a secure blockchain account in the browser. Lastly, you will use and run Ganache to create a local blockchain RPC server to test and develop against. P rerequisites Most of what you need is already installed. Angular needs Node and npm manager, which you have installed previously. Confirm the correct version is installed by running the libraries with the v flag, just as you have done in previous chapters. > node -v > npm -v In case you do not have npm and node, just run the following command: > brew install node Give npm ownership for your user so you won’t need to use sudo to install libraries. > sudo chown -R $USER:$GROUP ~/.npm > sudo chown -R $USER:$GROUP ~/.config It’s recommended that you upgrade npm to ensure you are using the latest version; at the time of writing, it’s 6.9.0. > [sudo] npm install -g npm [email protected] 360 Chapter 9 Build Dapps with Angular: Part I A ngular CLI Next, you need to install the Angular command-line interface (CLI). For Angular CLI, it’s recommended (but not required) to install Angular CLI with sudo and allow-root and ensure Angular CLI will have the correct privileges. You will be installing version 7.3.9, which is the latest stable release version of Angular. > sudo npm install -g @angular/[email protected] -unsafe-perm=true -allow-root + @angular/[email protected] added 363 packages from 197 contributors in 13.691s You could also install the latest version of Angular but your example code may break, with newer versions of Angular. > sudo npm install -g @angular/cli -unsafe-perm=true -allow-­root To verify installation went well, run the version flag, and you should see version 7.3.9; Figure 9-2 shows the expected output. > ng version 361 Chapter 9 Build Dapps with Angular: Part I Figure 9-2.  Angular CLI installation verification Create an Angular Project Now that you have the main tools and libraries installed, you can proceed and create your project from scratch by downloading other needed libraries, test libraries, and build scripts, as well as make your own folder structure; however, to expedite this process, you can use the Angular seed project that includes a skeleton project to quickly bootstrap your project. Using the Angular seed project can help you start development quickly and efficiently, following Angular’s best practices. There are pros and cons of using boilerplate skeleton code. You can decide on your own if you want to use this skeleton for future projects, but for this demo app, it is ideal. 362 Chapter 9 Build Dapps with Angular: Part I There are many ways you can create your project using the Angular seed skeleton. I will be showing you two options here: using the Angular CLI and using WebStorm. The ng new command will run a script that will create your app. You can run the CLI new command and give the name ethdapp as your app name. > cd ~/desktop > ng new ethdapp Would you like to add Angular routing? (y/N) y Which stylesheet format would you like to use? CSS Notice that I added routing here and decided to use CSS for styles. I will get more into these later in the chapter. Once installation is complete, it will output all the files that are created. CREATE ethdapp/ (1024 bytes) CREATE ethdapp/angular.json (3557 bytes) CREATE ethdapp/package.json (1313 bytes) … Change directories to the newly created folder and confirm you have the initial files and directories. > cd ethdapp Running the following command will analyze your package.json config file with recommendations: > ng update You can run the following command to follow the recommendations: > ng update -all 363 Chapter 9 Build Dapps with Angular: Part I Next, install Bower globally. Bower is a package manager that is used often with Angular. At the time of writing, it’s at version 1.8.8. > npm install -g bower > bower -v 1.8.8 Let’s do a walk-through of what was created in a workspace and the starter project files (see Figure 9-3). Figure 9-3.  Ethdapp files created by Angular CLI – A new workspace: This is the root folder named ethdapp. – e2e folder: This contains an end-to-end test project, located here: ethdapp/e2e. The testing folder includes the Jasmin library’s JSON configuration file. – src folder: This is your project folder, which includes all the files of your project. 364 • An initial skeleton app project, located here: ethdapp/src/app • The assets folder with the entry file index.html • Other configuration files Chapter 9 Build Dapps with Angular: Part I – .gitignore: Here you list any files and folders that you would like to ignore when you upload your project to Git. – angular.json: This is your project configuration file and includes information about your project. – package.json: This is the npm manager configuration file and includes all the libraries you will be using in your project. – README.MD: This is documentation about your project; this will be the “home page” document of your project and the first file developers will read to get instructions on how to get the project running. – tsconfig.json: This is the TypeScript config file. – tslint.json: This is the Lint config file used to set your best-practice formatting, spacing, and the like. Serve the Application To see your actual dapps, you will be using the ng serve command, which builds the app, starts the development server, watches the source files, and rebuilds the app as you make changes to those files. The -open flag opens the app in a browser on port 4200 here: http://localhost:4200/. Run the ng serve command with the open flag. > ng serve -open You should see the dapp running in your browser, as shown in Figure 9-4. 365 Chapter 9 Build Dapps with Angular: Part I Figure 9-4.  Angular seed app running in the browser The skeleton app includes links to a tour, documentation, and an Angular blog. By going through the “Tour of Heroes” and the CLI documentation, you can get a good understanding of how Angular works, and bookmarking the Angular blog can give you updates on future releases and announcements. To stop the application from serving, press Command+C in Terminal. 366 Chapter 9 Build Dapps with Angular: Part I Angular Project with WebStorm Another option for firing up the Angular seed project is utilizing the WebStorm IDE, which you have been using in previous chapters. WebStorm allows you to either import the seed project you created or create a new seed project. To import the ethdapp project you created with the Angular CLI ng new command, open WebStorm, select File ➤ Open, and navigate to the ethdapp directory. That’s it; WebStorm will automatically import the project. Alternatively, to start a new Angular seed project in WebStorm, select File ➤ New ➤ Project from the top menu. Next, select Angular CLI and name your project ethdapp. Use the drop-down menu to select the version of the Angular CLI, as shown in Figure 9-5. Figure 9-5.  Generating the Angular seed project in WebStorm 367 Chapter 9 Build Dapps with Angular: Part I Now that the project is created, you can run the same command, utilizing the Terminal tab in the bottom menu of WebStorm, as shown in Figure 9-6. > ng serve -open Figure 9-6.  Serving ethdapp in WebStorm’s Terminal You can download the skeleton application from the book repository: When you download your steps, make sure you run npm install because I stripped out the node module to decrease the size of the project. > npm install 368 Chapter 9 Build Dapps with Angular: Part I Note  I excluded node_modules, which holds all the project’s dependencies, from the project. It’s common not to include it with a project because of its size; you can install it with the npm install command. Ensure No Mismatch with Angular CLI Version You can create your Angular seed project either with WebStorm or through the ng command, and you need to check that there is no mismatch of the global Angular CLI with the local project Angular CLI. This can happen when setting files pointing to a previous version, or you may have used Angular in the past with an older version. What happens is that your local project Angular shows an older version than the global Angular installed on your computer. To ensure this is not the case, run any ng command, and if this issue exists, you will see the following error message: > ng Your global Angular CLI version (7.3.9) is greater than your local version (6.2.9). The local Angular CLI version is used. If you continue with these settings, you will be running version 6.x instead of 7.x. To fix this, what you need to do is uninstall the Angular CLI from your dev environment and then install version 7.x. > npm uninstall -save-dev angular-cli > npm install -save-dev @angular/[email protected] Notice that you use the -save-dev flag so the new version will be saved in your package.json project file. Now if you run the version command again, you should see the correct version with no warning messages. > ng -version Angular CLI: 7.3.2 369 Chapter 9 Build Dapps with Angular: Part I Now that you have ensured you are running the correct version of Angular CLI, you are ready to continue development and make changes to the seed starter app. Angular Components An Angular best practice is to use a Model View Controller (MVC)-style architecture. Angular supports coding with a separation of concerns just like any other mature framework. The Angular MVC includes the following three elements: – Model: This contains the application’s data and Angular data binding, which allows reflection of data. Note  reflection in relation to data binding, elements bound to a data and any data change is automatically reflected. For instance, you bind price change to multiple view elements and once the price change data is updated all the view elements are updated automatically. – View: This contains the HTML or a template and directives. – Controller: This is the glue holding the model and the view together. The controller takes the data, applies business logic, and sends the results to the view. As you probably recall, Angular’s welcome page opened when you were running the serve command. The welcome component is the application shell. The shell is controlled by an Angular component named AppComponent. Components are the fundamental building blocks of an Angular application. They display data on the screen, listen for user input, and take action based on that input. 370 Chapter 9 Build Dapps with Angular: Part I You will be creating a component called transfer that you will be using to transfer coins to another address. To create the transfer component, run the ng generate component command. > ng g c components/transfer Notice that you used the shortcuts g and c that stand for “generate” and “component,” respectively, but you can also use the full name instead of the abbreviation. The ng command generated the four following files for you: – transfer.component.css: Component’s specific CSS styles – transfer.component.html: Component template, written in HTML – transfer.component.spec.ts: Testing file – transfer.component.ts: Component class code, written in TypeScript These four files together act as the implementation of the transfer component. You can see the folder structure in Figure 9-7. Figure 9-7.  Transfer component file structure 371 Chapter 9 Build Dapps with Angular: Part I An application’s structure is usually created with a header, a footer, and a navigation menu so you can navigate to different partial views. Using this architecture of header and footer components can help you create different views and split the page view into separate files. Think of each piece as a stand-alone reusable UI module. Angular Seed promotes this type of architecture and comes with the welcome component already created. Let’s create a start component, a header, and footer components. > ng g c components/start > ng g c components/header > ng g c components/footer You can see in the output that each component generated the following files: CREATE src/app/components/[component-name]/[component-name]. component.css CREATE src/app/components/[component-name]/[component-name]. component.html CREATE ­src/app/components/[component-name]/[component-name]. component.spec.ts CREATE src/app/components/[component-name]/[component-name]. component.ts In addition to these files, you can open ethdapp/src/app/app.module. ts and notice that the app.module.ts file was modified every time you created a component. The app.module.ts file is one of the most important files in Angular; it’s the app controller written in TypeScript. The controller is a global file that will tie your components together, so every component you want to use in your app needs to be defined in that file. If you did not use the ng script, you will need to modify app.module.ts yourself to link to the new component. 372 Chapter 9 Build Dapps with Angular: Part I Since you used the CLI, these imports are included automatically for you: import { TransferComponent } from ‘./components/transfer/ transfer.component’; import { StartComponent } from ­’./components/start/start. component’; import { HeaderComponent } from ‘./components/header/header. component’; import { FooterComponent } from ‘./components/footer/footer. component’; R outing Module Another important file and a good practice to create is an app-routing module. This file acts as a controller to instruct Angular how to navigate to different views in your app. Normally to generate a route for your app, you do not need to manually do so, since during the creation of your app, you decided to create the routing file called app-routing. If you need to create the app-routing file, you can run the following the module command: > ng generate module app-routing -flat -module=app CREATE src/app/app-routing.module.ts UPDATE src/app/app.module.ts Notice that this time in your command you are using the full name generate module instead of just the first letters of g and m. Both options work the same way. The generate module command creates the initial code shown in Listing 9-1 for src/app/app-routing.module.ts. 373 Chapter 9 Build Dapps with Angular: Part I Listing 9-1. app-routing Initial Startup Code import { NgModule } from ‘@angular/core’; import { Routes, RouterModule } from ‘@angular/router’; const routes: Routes = []; @NgModule({ imports: [RouterModule.forRoot(routes)], exports: [RouterModule] }) export class AppRoutingModule { } The initial code includes an import statement to Angular code and module tag. Next, replace the pre-populated code of app-routing. module.ts file with the code in Listing 9-2. Listing 9-2. app-routing Code to Route Views import { NgModule } from ‘@angular/core’; import { CommonModule } from ‘@angular/common’; import { RouterModule, Routes } from ‘@angular/router’; import { StartComponent } from ‘./components/start/start. component’; import { TransferComponent } from ‘./components/transfer/ transfer.component’; const routes: Routes = [ { path: ”, redirectTo: ‘/start’, pathMatch: ‘full’ }, { path: ‘start’, component: StartComponent }, { path: ‘transfer’, component: TransferComponent } ]; @NgModule({ declarations: [], imports: [ RouterModule.forRoot(routes), CommonModule ], 374 Chapter 9 Build Dapps with Angular: Part I exports: [ RouterModule ] }) export class AppRoutingModule { } In Listing 9-2, you imported the view components you will be using; these are start and transfer. They will act as web pages on a web site or partial views on a mobile app. The route tells your app what view to match with what keyword, and lastly you set import statements to tell Angular who can access this module. Now that the routing is set, you can get the footer, header, and body of the page to display. All you have to do is open src/app/app.component. html and update from the welcome page’s HTML code to the following three lines: To test the changes you made to your application, you don’t need to publish your app again or run any scripts; just save the files and run the same serve command you ran before in Terminal. > ng serve ⌈wdm⌋: Compiled successfully. The serve script includes scripts to watch for changes in files and update your app automatically, so all you have to do when you make a change to your files is go back to the browser. Most of the time you won’t even need to refresh your web page; the changes will be there automatically. Navigate to http://localhost:4200 to see the changes. If you would like to go directly to the transfer page, all you have to do is add the keyword you selected at the end of the URL as you set up the routing mechanism: http://localhost:4200/transfer. See Figure 9-8. 375 Chapter 9 Build Dapps with Angular: Part I Figure 9-8.  Ethdapp header, footer, and transfer page You can download this step here: Styling an Angular App Your app at this point is not styled and only shows text with a header, the page, and a footer; however, before you start styling, it’s helpful to understand the Angular style architecture to ensure you don’t end up with a Cascading Style Sheets (CSS) file that is too big to manage. You can style your app on a global level with styles that you need across your entire app as well as a specific style unique to only one component. Additionally, it would be neat to sprint from zero to a styled app quickly. This can be done with Angular Material. Angular Material gives you a shortcut to get a consistent “look” to your app without all the hassle of thinking about cross-browser, cross-device programming. Let’s take a look. A ngular-Style Architecture Angular is set up to have a global CSS file. That CSS file is called style. css, and you can find it in the root of the project. src/style.css holds the styles that you want to use for your entire app, such as fonts, themes, styles for all the components, and so on. 376 Chapter 9 Build Dapps with Angular: Part I As you have seen, each component also includes a private CSS file. The specific component CSS file is where you put styles that are unique and used only for that component. For instance, /src/app/components/footer/footer.component.css holds the styles specific for the footer component. A ngular Material Right now, your starter application is fast because it includes minimal code; however, there is a potential performance issue as you add more and more components, assets, and style to your app. You can get your app bloated easily, and every millisecond dealy counts. The other potential issue is testing. All the different browsers, versions of browsers, screen sizes, and devices need to be tested, and creating your pages from scratch will require rigid testing and a quality assurance (QA) team to ensure it works consistency across devices. Angular Material solves all these issues plus provides accessibility and internationalization. That is because Angular Material is optimized for Angular and built by the Angular team, so it integrates seamlessly with Angular. It has already passed all these compatibility tests. For more information, check the Angular Material getting started page: Install Angular Material There are a few ways to install Material. Because you have installed the Angular DevKit, you are able to just run the ng add command to get the Angular Material library. You need to first install cdk because it’s a dependency. > ng add @angular/cdk 377 Chapter 9 Build Dapps with Angular: Part I Next, install Material. > ng add @angular/material Notice that the output asks you which theme color you would like with links. I will cover themes in the next section of this chapter, but for now, select the first or any color you prefer. ? Choose a prebuilt theme name, or “custom” for a custom theme: (Use arrow keys) □ Indigo/Pink [ Preview: https://material.angular. io?theme=indigo-pink ] Deep Purple/Amber [ Preview: https://material.angular. io?theme=deeppurple-amber ] Pink/Blue Grey [ Preview: https://material.angular. io?theme=pink-bluegrey ] Purple/Green [ Preview: https://material.angular. io?theme=purple-green ] You can also set up gesture recognitions and animations. ? Set up HammerJS for gesture recognition? Yes ? Set up browser animations for Angular Material? Yes The expected output should be showing the files that were updated: UPDATE UPDATE UPDATE UPDATE UPDATE package.json angular.json src/app/app.module.ts src/index.html src/styles.css Import Angular Material Modules Next, you want to modify your app to have Angular Material include animations, Material icons, gesture support, and component modules. 378 Chapter 9 Build Dapps with Angular: Part I In your project, you will only be using component modules and not all the features that Angular Material has to offer; what you need to do is import NgModule for each component you want to use. Open src/ app/app.module.ts and add the import statements. import { MatButtonModule, MatCheckboxModule, MatInputModule, MatSelectModule, MatDatepickerModule, MatNativeDateModule } from ‘@angular/material’; Next, update the import statements of @NgModule to include the Material modules you imported. imports: [ BrowserModule, AppRoutingModule, BrowserAnimationsModule, MatButtonModule, MatInputModule, MatDatepickerModule, MatNativeDateModule, MatCheckboxModule, MatSelectModule ] That’s it. You can now have access to the Angular Material components you included. 379 Chapter 9 Build Dapps with Angular: Part I Theme Your Angular Material App Now that you have access to the Angular Material components, you can use themes to style them. A theme is a set of colors that will be used on your Angular Material components. In Angular Material, a theme is created by creating multiple palettes. – Primary palette: These are the colors most used across all screens and components. – Accent palette: These are the colors used for the button and interactive elements. – Warn palette: These are the colors for errors. – Foreground palette: These are the colors for text and icons. – Background palette: These are the colors for an element’s backgrounds. In Angular Material, all theme styles are generated statically at build time to avoid slowing the app on startup. Angular Material comes prepackaged with several prebuilt theme CSS files. As you probably recall, you had an option of selecting a theme to use when you installed Material. These theme files also include all of the styles for the core (styles common to all components), so you have to include only a single CSS file for Angular Material in your app. You can include a theme file directly into your application from @angular/material/prebuilt-themes. These are the available prebuilt themes: – deeppurple-amber.css – indigo-pink.css – pink-bluegrey.css – purple-green.css 380 Chapter 9 Build Dapps with Angular: Part I You are using Angular CLI here, so you can simply include the style you want in the global src/styles.css file. Originally it has this initial precode: html, body { height: 100%; } body { margin: 0; font-family: ‘Roboto’, sans-serif; } Add the following import statement at the top of the document: @import “[email protected]/material/prebuilt-themes/indigo-pink.css”; While you have the src/style.css file open, you can also create a style for a container, a paragraph, and a button that you can use across your app for your pages. p { padding-left: 20px; font-size: 12px; } .container { margin-right: auto; margin-left: auto; padding: 20px 15px 30px; width: 750px; } button { color: #ffffff; background-color: #611BBD; border-color: #130269; display: inline-block; margin-bottom: 0; font-weight: normal; text-align: center; vertical-align: middle; 381 Chapter 9 Build Dapps with Angular: Part I touch-action: manipulation; cursor: pointer; white-space: nowrap; padding: 6px 12px; font-size: 12px; line-height: 1.42857143; border-radius: 4px; -webkit-user-select: none; -moz-user-select: none; -ms-user-select: none; user-select: none; } You can compare your files with mine: the-blockchain-developer/chapter9/ C reating Content At this point, you have a skeleton app with a header, body, and footer. The body can be switched between your start page and transfer page by changing the URL in the browser. You also imported and injected Material modules and set up global styles for your app. The next step is to create actual content to replace the temporary text message you placed in your header, footer, and start components. F ooter Component For the footer component, you will just replace the message for your company copyright. To do so, all you need to do is open src/app/components/ footer/footer.component.html and replace the default code.

footer works!

382 Chapter 9 Build Dapps with Angular: Part I Replace the code by creating a div container with the style you added to the global CSS file.

Copyright (c) 2019 Company Name. All Rights Reserved.

You are also going to create a specific style for the footer component, so every time you use the p tag, your font will be size 12px with no padding on the left. Open src/app/components/footer/footer.component.css and insert the following: p { padding-left: 0; font-size: 11px; } Notice that you defined the

tag twice, once in the global CSS file and one at the component level. What’s going to happen is that the global

tag will be overwritten by the component

, so you can use the

tag for your footer and a different

tag for other components such as the start and transfer pages while keeping your HTML code free of CSS code. Header Component For the header component, you will create a navigation menu to be able to switch between the start page and the transfer page. For styles specific to the header component, open src/app/components/header/header. component.css and add the nav list styles. 383 Chapter 9 Build Dapps with Angular: Part I .nav { margin-bottom: 0; padding-left: 0; list-style: none; } li { display: block; float: left; width: 100px; height: 25px; padding: 5px; } .nav>li>a { margin-bottom: 0; padding-left: 0; font-weight: 500; font-size: 12px; text-transform: uppercase; position: relative; } For src/app/components/header/header.component.html, you create a container and a list of the two links to the pages start and transfer. To do so replace the initial code:

header works!

with the following;

  • 384 Chapter 9 Build Dapps with Angular: Part I
  • home
  • transfer

The working dapp now includes basic styling and functional navigation, as shown in Figure 9-9. Figure 9-9.  Ethdapp with basic styling and working navigation You can download this step here: 385 Chapter 9 Build Dapps with Angular: Part I T ransfer Component The transfer component will hold a form that you will submit to transfer Ethereum coins from one account address to another. You will be using the forms module to expedite creating your form. To do so, you need to include the Material FormsModule and ReactiveFormsModule form modules in app.module.ts just as you did with other Material modules. Open src/app/app.module.ts and add the following import statement: import { FormsModule, ReactiveFormsModule } from ‘@angular/forms’; You also want to update the import statement. imports: [ FormsModule, ReactiveFormsModule, .. ] You will be using the tag, which represents a component that wraps several Angular Material components together and applies common text field styles such as the underline, floating label, and hint messages. This will expedite development as you won’t need to implement all of these and test them on multiple devices/browsers. The form field is the wrapper component named . You can use any of the form field controls (such as input, textarea, list, etc.). You can find information about mat-forms here: https://material. For src/app/components/transfer/transfer.component.ts, you will update the initial code. First you need to import the components you will be using; in this case, you need to initialize the class and use form, form control, and validators. import {FormBuilder, FormControl, FormGroup, Validators} from ‘@angular/forms’; 386 Chapter 9 Build Dapps with Angular: Part I Then you need to update the component definition to implement the OnInit method. export class TransferComponent implements OnInit { You will be using a flag to indicate whether the form was submitted and to create an instance of a form group, as well as an object called user, to hold the user’s information. formSubmitted: Boolean = false; userForm: FormGroup; user: any; To validate your form, you will define the messages in case the form is not filled in correctly. Each form control needs to be defined with the required fields and messages. account_validation_messages = { ‘transferAddress’: [ { type: ‘required’, message: ‘Transfer Address is required’ }, { type: ‘minLength’, message: ‘Transfer Address must be 42 characters long’ }, { type: ‘maxLength’, message: ‘Transfer Address must be 42 characters long’ } ], ‘amount’: [ { type: ‘required’, message: ‘Amount is required’ }, { type: ‘pattern’, message: ‘Amount must be a positive number’ } ], ‘remarks’: [ { type: ‘required’, message: ‘Remarks are required’ } ] }; 387 Chapter 9 Build Dapps with Angular: Part I When you create the constructor, you need to include the FormBuilder component to be able to generate the form. constructor(private fb: FormBuilder) { } When your component gets init, you will set the formSubmitted flag to false and set default values for the user’s information. You then will call a method to go fetch the user’s account and balance, which you will implement later. Lastly, you will call the createForms method that will generate the form. ngOnInit() { this.formSubmitted = false; this.user = {address: ”, transferAddress: ”, balance: ”, amount: ”, remarks: ”}; this.getAccountAndBalance(); this.createForms(); } The createForms method will generate the form controls by passing the validators and data. createForms() { this.userForm ={ transferAddress: new FormControl(this.user.transferAddress, Validators.compose([ Validators.required, Validators.minLength(42), Validators.maxLength(42) ])), amount: new FormControl(this.user.amount, Validators. compose([ Validators.required, Validators.pattern(‘^[+]?([.]d+|d+[.]?d*)$’) 388 Chapter 9 Build Dapps with Angular: Part I ])), remarks: new FormControl(this.user.remarks, Validators. compose([ Validators.required ])) }); } The getAccountAndBalance method will set the user account’s address and balance; for now you are using dummy data, but you will implement the actual service later in this chapter. getAccountAndBalance = () => { const that = this; that.user.address = ‘0xd8d0101f83e79fb4e8d21134f5325e64816b d6a0’; that.user.balance = 0; // TODO: fetch data } Lastly, once you submit your form, you need a method to handle the data and call the service. submitForm will be used by checking whether the form is valid, and then later you will call the service component you will create. submitForm() { if (this.userForm.invalid) { alert(‘transfer.components :: submitForm :: Form invalid’); return; } else { console.log(‘transfer.components :: submitForm :: this. userForm.value’); console.log(this.userForm.value); 389 Chapter 9 Build Dapps with Angular: Part I // TODO: service call } } } For transfer.component.html, you will set the form tag to call the submitForm method once the form is submitted. Next, you will create the wrapping divs and use data binding to display the user’s account address and balance. Address: {{user.address}} Balance: {{user.balance}} Eth Notice that you have used the transfer-container style, which you have not yet defined; you will define it in your CSS file, and it will be used to format your form. For form controls, you need input boxes for the account you are transferring the funds to, the amount, and a message. You also need to set up your validations. 390 Chapter 9 Build Dapps with Angular: Part I {{validation. message}} {{validation.message}} {{validation.message}} 391 Chapter 9 Build Dapps with Angular: Part I Lastly, remember to close the divs and form, as well as include a submit button. Transfer Ether For transfer.component.css, you will be using the transfer-­ container div to format your form horizontally. .transfer-container { display: flex; flex-direction: column; } .transfer-container > * { width: 100%; } That’s it. Now you can check your dapp in the browser, and you should be able to see the user’s default data, test the form, validate it, and submit the form. See Figure 9-10. 392 Chapter 9 Build Dapps with Angular: Part I Figure 9-10.  Ethdapp transfer page including user’s info, validators, and submit button You can download this step here: A ngular Directives Creating directives in Angular gives you the ability to create your own custom HTML tags with just a few lines of code, just as you saw in the Material form. You were able to include custom tags that wrap many components. At a high level, directives are markers on a DOM element. These markers can point to any DOM component, from an attribute to an element name or even a comment or CSS class. These markers then tell the AngularJS’s HTML compiler to attach a specified behavior or to transform the entire DOM element and its children based on specific logic. Angular comes with many of these directives built-in. However, during development, it’s a good chance you will be creating your own directives. Your dapp is simple now, so you don’t need to create any directive, and it’s beyond the scope of this chapter to explain this. When you do need to 393 Chapter 9 Build Dapps with Angular: Part I generate a skeleton directive, use the Angular CLI just as you generated other components. > ng generate directive {directive-name} Although you are not creating a directive in your app, I wanted to introduce you to the concept as it’s an integral part of creating an Angular project. Summary In this chapter, you took a deep dive into what a dapp is and looked at dapp classifications and projects. You learned how to start your own dapp project by breaking the process into five steps: writing a white paper, launching an ICO, developing the dapp, launching it, and marketing your dapp. You then looked at why to use Angular. Next, you created an Angular dapp, first ensuring the prerequisites were installed and installing the Angular CLI. Then you created an Angular project and served the application. Next, you learned how to import your Angular project to WebStorm or create a new project. You looked at the pieces that make Angular such as components, modules, and directives. You also learned how to style the dapp by understanding Angular-style architecture and working with Angular Material. You started building components and created content; you split your app into a footer, header, and body and created a custom component called transfer that includes a form to be able to later transfer tokens. In the next chapter, you will create a transfer smart contract and a Truffle development project as well as connect to the Ganache development network. You will learn how to work with the Ethereum network via Truffle and test your smart contract. You also will link your dapp with the Ethereum Network’s web3 library and connect via MetaMask. 394 Build Dapps with Angular: Part II In the previous chapter, you started developing your dapp. Specifically, you learned about dapp classifications and projects and that you can break your own dapp project into five steps. You then looked at why to use Angular and its benefits. Next, you created an Angular project, first ensuring the prerequisites were installed and then installing the Angular CLI. You looked at the pieces that make up Angular such as components, modules, and directives. You also learned how to style a dapp by understanding Angular-style architecture and working with Angular Material. You started building your own custom components and creating content; you split your app into a footer, header, and body and created a custom transfer component that you will be using in this chapter. In this chapter, I will cover the following: • Creating the dapp’s smart contract with Truffle • Integrating a smart contract in your dapp’s Angular project • Linking and connecting your dapp to the Ethereum network Chapter 10 Build Dapps with Angular: Part II You will be utilizing the tools I have been covering so far: the Angular CLI, Truffle, ganache-cli, and MetaMask. You will create a smart contract that you will use for your dapp with Truffle, and then you’ll use the web3 library to connect to the Ethereum local network and call the smart contract’s functions and events. MetaMask will be used to manage and connect to your account. Tip  It’s recommended that you complete the previous chapter and Chapter 5 prior to going through this chapter in order to fully understand the examples here, which build on the concepts, tools, and installed libraries from Chapters 9 and 5. Transfer a Smart Contract You already have the front-end logic to transfer tokens in your app from the previous chapter; however, you don’t have a smart contract to interact with the blockchain. Smart contracts can be created before the front-end portion, after, or in parallel (if you work with a team of developers). You already created an Ethereum smart contract in Chapter 5, so the steps in this section should be familiar to you. Feel free to revisit Chapter 5 to refresh your memory, as I won’t go into much detail regarding the tools and commands used in this chapter. To get started, you will create a new folder in your ethdapp project to hold the Truffle project. You can download the latest step, where you left off from, here: chapter9/ In real-life projects with multiple developers, the smart contract could be a separate project. For simplicity, you will be including it in your project so you can utilize the WebStorm Terminal window’s bottom tab to run commands. 396 Chapter 10 Build Dapps with Angular: Part II Start by creating a folder called truffle inside your project and initialize Truffle to create the project. You can see the expected output in Figure 10-1. > mkdir ethdapp/truffle > cd truffle > truffle init Figure 10-1.  Output of creating a Truffle project Tip  If you get errors such as “Error: Truffle Box,” uninstall Truffle, and then re-install it and try again. To re-install truffle in case of error messages, remove truffle globally and install it again. > npm uninstall -g truffle If you do not have Truffle installed or need to re-install Truffle globally, run the install command. > npm install -g truffle 397 Chapter 10 Build Dapps with Angular: Part II After re-installing or performing a fresh install, run the truffle init command again and make sure you run the test in a new Terminal window to ensure the changes were applied. > truffle compile > truffle migrate > truffle test You can compare your results with mine, shown in Figure 10-2. Figure 10-2.  Truffle compiling, migrating, and testing your project Create a Smart Contract You’ll create a smart contract and call it Transfer.sol; put it here: truffle/contracts/Transfer.sol. The contract will allow you to transfer funds from one account to another. First navigate to the location of the contracts in Truffle and use an editor to create a new file. > cd ethapp/truffle/contracts > vim Transfer.sol 398 Chapter 10 Build Dapps with Angular: Part II The complete Transfer.sol code is listed here: pragma solidity ^0.5.0; contract Transfer { address payable from; address payable to; constructor() public { from = msg.sender; } event Pay(address _to, address _from, uint amt); function pay( address payable _to ) public payable returns (bool) { to = _to; to.transfer(msg.value); emit Pay(to, from, msg.value); return true; } } Let’s walk through the code. First you need to define the solidity version you will be using and the contract name. pragma solidity ^0.5.0; contract Transfer { Next, define the from and to addresses and the constructor. address payable from; address payable to; constructor() public { from = msg.sender; } 399 Chapter 10 Build Dapps with Angular: Part II You will be using a Pay event that will be dispatched once the pay function is used. event Pay(address _to, address _from, uint amt); The pay function uses the Pay event to interact with the network and do the actual transfer. function pay( address payable _to ) public payable returns (bool) { to = _to; to.transfer(msg.value); emit Pay(to, from, msg.value); return true; } } That’s it. You kept it basic and simple with only one event and one function. You can download this step from here: the-blockchain-developer/chapter10/ Create the Truffle Development Network The next step is to replace the truffle/truffle-config.js file with the following configuration: module.exports = { networks: { development: { host: “”, port: 8545, network_id: “*”, gas: 5000000, 400 Chapter 10 Build Dapps with Angular: Part II gasPrice: 100000000000 } } }; Notice that you point to port 8545, which will help you when you run MetaMask later in this chapter. Deploy the Smart Contract The other configuration file you need is the deploy contract file. Create a deployment file and call it truffle/migrations/2_deploy_contracts.js. In this config file all you do is point to the Transfer smart contract SOL code you created. var Transfer = artifacts.require(“./Transfer.sol”); module.exports = function(deployer) { deployer.deploy(Transfer); }; Now you are ready to create your network on port 8545 with Ganache, so navigate to the Truffle project, and run this command: > cd ethdapp/truffle > ganache-cli -p 8545 Tip  If you get any errors such as “NODE_MODULE_VERSION mismatch,” uninstall and re-install ganache-cli. Then open a new Terminal window and ensure it’s running correctly. 401 Chapter 10 Build Dapps with Angular: Part II To re-install ganache-cli if needed, run this: > npm uninstall -g ganache-cli > npm install -g ganache-cli To ensure it’s running correctly, run this: > ganache-cli help Next, in a new Terminal window, let’s compile and deploy your contract while ganache is still running. > truffle compile The compile output should provide success, creating your contract in the Contract folder. Compiling ./contracts/Transfer.sol… Writing artifacts to ./build/contracts The file that was created is Transfer.json, which you will be using in your dapp to interact with the network. Next, you will deploy your contract with the migrate command. > truffle migrate -network development The output should confirm the contract was migrated to the network, as shown in Figure 10-3. 402 Chapter 10 Build Dapps with Angular: Part II Figure 10-3.  Truffle migrate project The output summary should also show that the deployment went well and a charge. Summary ======= > Total deployments: 2 > Final cost: 0.0525573 ETH Truffle Console Now that you have the contract compiled and deployed, to interact with the network, start a console, as shown here: > truffle console -network development A good resource for the commands you can run against the Truffle CLI is at the Ethereum JavaScript API wiki page here: ethereum/wiki/wiki/JavaScript-API. 403 Chapter 10 Build Dapps with Angular: Part II Accounts If you run getAccounts, you’ll get a list of accounts associated with your wallet. truffle(development)> web3.eth.getAccounts() [ ‘0x1eFf25A40C82EA65BC88E45d02368897EC922FEf’, ‘0xC135058b33d5df78636Cf14b74F281f95c4a407c’, ‘0xe682300Ef633F7d4f0d8Cb07c1bAD5d9B4eaE974’ ….] You can then define address1 and address2 as the first and second accounts. truffle(development)> web3.eth.getAccounts().then( function(a) {address1=a[0]}) undefined truffle(development)> web3.eth.getAccounts().then( function(a) {address2=a[1]}) undefined Now that they are defined, you can call them and get the first and second accounts in the output. truffle(development)> address1 ‘0x1eFf25A40C82EA65BC88E45d02368897EC922FEf’ truffle(development)> address2 ‘0xC135058b33d5df78636Cf14b74F281f95c4a407c’ You can also use getBalance to get the balance you have in these addresses. truffle(development)> web3.eth.getBalance(address1) ‘99942134400000000000’ truffle(development)> web3.eth.getBalance(address2) ‘100000000000000000000’ 404 Chapter 10 Build Dapps with Angular: Part II Test the Transfer of a Smart Contract Now that you have defined two addresses and you know the balance in these accounts, you can define your contract and pass some funds between the accounts. To do so, first define the contract and call it transferSmartContract. truffle(development)> Transfer.deployed(). then(function(instance){transferSmartContract = instance;}) undefined Next, run the transferSmartContract variable you defined to ensure it worked and show the object value. > transferSmartContract Now you can transfer funds with your smart contract between the two accounts. Account 2 holds a nice round number, so you will transfer 5 eth. >, {from: address1, value: 5}); The command output shows information about the transaction and mining. Now you are able to see the balance updated. > web3.eth.getBalance(address1); ‘99942134399999999995’ > web3.eth.getBalance(address2); ‘100000000000000000005’ As you can see, the balance changed, and you were able to transfer tokens between two addresses. 405 Chapter 10 Build Dapps with Angular: Part II Link with the Ethereum Network You got your contract working in Terminal; the next step is for your dapp to interact with the contract. This is done via web3.js, which is a collection of libraries allowing you to interact with a local or remote Ethereum node using an HTTP or IPC connection. First navigate back into your Angular project folder and then install web3.js with the flag -save to save the library you are installing. > cd ethdapp/ > npm install web3 -save + [email protected] If installation went well, you will see in the output that the version did install. At the time of writing, web3 is at version 1.0.0-beta55. You also need to install truffle-contract, which provides wrapper code that makes interaction with your contract easier. At the time of writing, the latest is version 4.0.7 but will probably change by the time you are reading this book. > npm install truffle-contract -save + [email protected] Tip  web3 version 1.0.0 beta and truffle-contract version 4.0.15 are the latest versions and compatible with Angular 7.3.x. However, this can change, so watch the version you are installing to ensure it’s compatible and to avoid errors. Re-install with exact @[version], for instance @4.0.15, if you run into compatibility issues. 406 Chapter 10 Build Dapps with Angular: Part II Transfer Service Now that you have your libraries installed, you can continue. In this section, you will create and write a service class. A service class is going to be your front-end middle layer to interact with web3. To get started, you can utilize the ng s flag, which stands for “service.” > ng g s services/transfer -module=app.module CREATE src/app/services/transfer.service.spec.ts CREATE src/app/services/ transfer.service.ts You will replace the service class’s initial code with logic to interact with web3. First you will define the libraries you will be using, which are the Angular core and the truffle-contract and web3 libraries you installed. import { Injectable } from ‘@angular/core’; const Web3 = require(‘web3’); import * as TruffleContract from ‘truffle-contract’; Next, you will define three variables you will be using later: require, window, and tokenAbi. Notice that tokenAbi points to the ABI file you compiled from the contract SOL file. declare let require: any; declare let window: any; const tokenAbi = require(‘../../../truffle/build/contracts/ Transfer.json’); You need access to root to interact with web3, so you need to inject it into your project. @Injectable({ providedIn: ‘root’ }) 407 Chapter 10 Build Dapps with Angular: Part II Next, define the class definition, the account and web3 variables, and init web3. export class TransferService { private _account: any = null; private readonly _web3: any; constructor() { if (typeof window.web3 !== ‘undefined’) { this._web3 = window.web3.currentProvider; } else { this._web3 = new Web3.providers.HttpProvider(‘http:// localhost:8545’); } window.web3 = new Web3(this._web3); console.log(‘transfer.service :: this._web3’); console.log(this._web3); } Notice that you wrapped console.log messages around the code so you can see the messages in the browser console messages section under developer tool mode to help you understand what’s happening. To do so open the browser in a developer tool mode. For Chrome, select View Developer View ➤ Developer ➤ Developer Tools. You need an async method to get the account address and balance, so you can use a promise function. If your account was not retrieved previously, you’ll call web3.eth.getAccounts just as you did in Terminal to retrieve the data. You also need error code if something goes wrong. private async getAccount(): Promise { console.log(‘transfer.service :: getAccount :: start’); if (this._account == null) { 408 Chapter 10 Build Dapps with Angular: Part II this._account = await new Promise((resolve, reject) => { console.log(‘transfer.service :: getAccount :: eth’); console.log(window.web3.eth); window.web3.eth.getAccounts((err, retAccount) => { console.log(‘transfer.service :: getAccount: retAccount’); console.log(retAccount); if (retAccount.length > 0) { this._account = retAccount[0]; resolve(this._account); } else { alert(‘transfer.service :: getAccount :: no accounts found.’); reject(‘No accounts found.’); } if (err != null) { alert(‘transfer.service :: getAccount :: error retrieving account’); reject(‘Error retrieving account’); } }); }) as Promise; } return Promise.resolve(this._account); } Similarly, you need a service method to interact with and get the balance of the account. You use web3.eth.getBalance just as you did in Terminal and wrap some error checking. You also set this as a promise. The reason you need a promise is that these calls are async, and JavaScript is not. 409 Chapter 10 Build Dapps with Angular: Part II public async getUserBalance(): Promise { const account = await this.getAccount(); console.log(‘transfer.service :: getUserBalance :: account’); console.log(account); return new Promise((resolve, reject) => { window.web3.eth.getBalance(account, function(err, balance) { console.log(‘transfer.service :: getUserBalance :: getBalance’); console.log(balance); if (!err) { const retVal = {account: account, balance: balance}; console.log(‘transfer.service :: getUserBalance :: getBalance :: retVal’); console.log(retVal); resolve(retVal); } else { reject({account: ‘error’, balance: 0}); } }); }) as Promise; } Last, you need a method to pass the values from your form and transfer payment from one account to another. Use the contract pay method and wrap some error checking. transferEther(value) { const that = this; console.log(‘transfer.service :: transferEther to: ‘ + value.transferAddress + ‘, from: ‘ + that._account + ‘, amount: ‘ + value.amount); return new Promise((resolve, reject) => { console.log(‘transfer.service :: transferEther :: tokenAbi’); 410 Chapter 10 Build Dapps with Angular: Part II console.log(tokenAbi); const transferContract = TruffleContract(tokenAbi); transferContract.setProvider(that._web3); console.log(‘transfer.service :: transferEther :: transferContract’); console.log(transferContract); transferContract.deployed().then(function(instance) { return value.transferAddress, { from: that._account, value: value.amount }); }).then(function(status) { if (status) { return resolve({status: true}); } }).catch(function(error) { console.log(error); return reject(‘transfer.service error’); }); }); } } Now that you have the transfer service complete, you can connect transfer.component to get the user’s account address and balance and be able to transfer funds once the form is filled in. First you need to define the service component you created. Open src/ app/component/transfer/transfer.component.ts and add the import statement at the top of the document. import {TransferService} from ‘../../services/transfer.service’; 411 Chapter 10 Build Dapps with Angular: Part II For the component definition, add TransferService as a provider. @Component({ .. providers: [TransferService] }) Also, add TransferService to the constructor so you can use it in your class. constructor(private fb: FormBuilder, private transferService: TransferService) { } Next, update the getAccountAndBalance method to include a call to the service class and retrieve the user actual account and balance. getAccountAndBalance = () => { const that = this; this.transferService.getUserBalance(). then(function(retAccount: any) { that.user.address = retAccount.account; that.user.balance = retAccount.balance; console.log(‘transfer.components :: getAccountAndBalance :: that.user’); console.log(that.user); }).catch(function(error) { console.log(error); }); } Lastly, update submitForm to call transferEther to transfer and pay. Replace the submitForm TODO comments shown here with the call to the service calls: // TODO: service call 412 Chapter 10 Build Dapps with Angular: Part II Then pass the data the user submitted: this.transferService.transferEther(this.userForm.value). then(function() { }).catch(function(error) { console.log(error); }); }); You can download the complete step from here: Apress/the-blockchain-developer/chapter10/ C onnect to MetaMask At this point, your dapp code is complete. However, if you test your dapp now, web3 won’t be able to connect to an account. What you need to do is connect to MetaMask. There is a privacy issue related to dapps where malicious web sites are able to inject code to view users’ activities and Ethereum addresses and then find the balance, transaction history, and personal information. These malicious sites are then able to initiate unwanted transactions on a user’s behalf, and the user accidentally may approve an unauthorized transaction and lose funds. To avoid these issues and to connect your Angular service, you will connect the browser to the network via MetaMask. You have already used MetaMask, so you should have it installed. Let’s back up for a second. As you’ll recall, you started a network via ganache-cli on port 8545. > ganache-cli -p 8545 And you connected Truffle to the network. > truffle migrate -network development 413 Chapter 10 Build Dapps with Angular: Part II Then you were able to connect on port 8545 and run commands in Terminal. You can now connect MetaMask in a browser. To connect, select MetaMask and select Localhost 8545 in the drop-down menu. See Figure 10-4. Figure 10-4.  Connecting MetaMask to a private network on port 8545 Notice that you picked port 8545 earlier in this chapter. It’s the default port on MetaMask, so it’s easy to connect to on your private network by selecting the drop-down menu item instead of pointing to a custom port. However, when you check the list of accounts, you don’t see any accounts. The reason you don’t see accounts is that every time you start your network, you need to update the accounts. There are two ways to update MetaMask with the list of accounts. Option 1: When you run Ganache, use the m flag to pass the mnemonic that represents the private keys you had in Ganache. For instance, the command will look like this: > ganache-cli -p 8545 -m ‘journey badge medal slender behind junk develop produce spy enemy transfer room’ 414 Chapter 10 Build Dapps with Angular: Part II Option 2: When you run ganache-cli, you will see the list of accounts, private keys, and mnemonics. > ganache-cli -p 8545 Look for this output and copy the mnemonic. HD Wallet ================== Mnemonic: journey badge medal slender behind junk develop produce spy enemy transfer room Base HD Path: m/44’/60’/0’/0/{account_index} Then, log out of MetaMask and paste the mnemonic manually. Click the right button and select “Log out,” as shown in Figure 10-5. Figure 10-5.  MetaMask logout of account After logging out, the welcome screen comes back with a link under it that says, “Import using account seed phrase.” Click that link, as shown in Figure 10-6. 415 Chapter 10 Build Dapps with Angular: Part II Figure 10-6.  MetaMask welcome page Now you can paste the mnemonic by selecting a password and clicking Restore, as shown in Figure 10-7. Figure 10-7.  Restoring MetaMask account using a mnemonic 416 Chapter 10 Build Dapps with Angular: Part II Test Your Dapp Functionality Now you are finally ready to test your dapp. Once the browser gets refreshed, you will see the address and balance. Next, fill in the form and initialize a transfer. Notice that MetaMask opens to confirm the transfer. This is an extra measurement of security to ensure only authorized transfers get approved. See Figure 10-8. Figure 10-8.  MetaMask notification to complete a transfer W here to Go from Here Continue working and improving the dapp you created. For instance, you could do the following: – Create a user service class and a shared service class to hold users’ information and shared information – Create a login/logout service 417 Chapter 10 Build Dapps with Angular: Part II – Create an option to switch between accounts – Create a side menu to better navigate the app – Update the smart contract and add more methods and events Summary In this chapter, you created a transfer smart contract and Truffle development project as well as connected to the Ganache local development network. You learned how to work with the Ethereum network via Truffle and how to test your smart contract. You test the transfer of funds using your smart contract via the command line. Lastly, you linked your dapp with the Ethereum network using an Angular TransferService component that you created. Using the web3 library, you made some service calls. Lastly, you connected to MetaMask to manage your accounts. In the next chapter, you will learn about blockchain security and compliance. 418 Security and Compliance As you have seen, most blockchains are decentralized, and the identity of each party is normally protected; however, most blockchain-related code involves storing some confidential data such as a user’s personal information, passwords, cryptocurrency, and wallets. Blockchain-related code has characteristics that make it a magnet for hackers. – The code is usually open source for transparency and to promote contributors. – Much of the code out there is not mature enough to be considered release grade. – In cryptocurrency-related blockchains, losing data can mean more than just a mere privacy breach. Once funds are transferred, it’s not easy to track them, and the transfer is likely to be irreversible. These concerns have been magnified as blockchain technology has become more popular and more people are invested in blockchain. In fact, there have been increasing reports regarding blockchain-related losses, and new attacks are being published on news outlet almost daily. For instance, during the writing of this book, $40 million was stolen from the Chapter 11 Security and Compliance Binance exchange. Additionally, in the past 12 months, an estimated $23 million was stolen in double spending attacks. Similarly, a staggering $1.5 billion was stolen from crypto exchanges. Postmortem reports sometimes show a sophisticated heist method that you would need to be a genius to prevent. However, most attacks can be prevented easily and are nothing more than a simple oversight or the result of not using tools capable of revealing vulnerabilities. “Intellectuals solve problems; geniuses prevent them.” —Albert Einstein As professionals, it is your responsibility to your customers who place their trust in you, as well as your reputation and fiduciary responsibility, to mitigate these risks and ensure data is protected. Security measures should be considered during all stages of the development cycle; in fact, security should be the most important aspect of your development. However, it is unrealistic to presume that I will be able to cover all aspects of security in just one chapter, as there are thousands of specific known attacks. In addition to security, another aspect that needs to be addressed is regulation. Regulators have been shaping technology in general and the blockchain industry in particular, and there are multiple regulations to abide by in each geographic location. Because new attacks are invented daily, regulatory laws are revised often. Understanding common attacks, security, privacy, compliance, and regulations can be a challenging task. In this chapter, I will give you insights into the security mind-set and help you become more aware of security, privacy, and compliance. This chapter is split into three parts. • 420 Security readiness: I will cover areas you should be taking into account before and while developing your platform. Chapter 11 Security and Compliance • Common blockchain attacks: I will cover some of the most famous and common blockchain attacks. • Development cycle: I will provide you with a recommended development cycle so you can take into account security and compliance.