Build Your Own Blockchains in JavaScript from Zero

August 19, 2017
blockchain
javascript

Build Your Own Blockchains in JavaScript from Zero (Scratch)

Decentralize Payments

What’s Blockchain?

Distributed Database?
Hyper Ledger Book?
Consensus with Proof-of-Work or Proof-of-Stake?
Digital Fingerprints? Cryptographic Hashes?
Lottery? Central Bank?
Byzantine-Generals Solution?

Yes. Yes. Yes. Blockchain! Blockchain! Blockchain!

(Source: openblockchains/whatsblockchain)

Code, A Blockchain in JavaScript in 20 Lines

What’s Blockchain?

It’s a list (chain) of blocks linked and secured by digital fingerprints (also known as crypto hashes).

const SHA256 = require( "js-sha256" )     // for hash checksum digest function SHA256

class Block {

  constructor(index, data, previousHash) {
    this.index        = index
    this.timestamp    = new Date()
    this.data         = data
    this.previousHash = previousHash
    this.hash         = this.calcHash()
  }

  calcHash() {
    var sha = SHA256.create()
    sha.update( this.index.toString() +
                this.timestamp.toString() +
                this.data +
                this.previousHash )
    return sha.hex()
  }

(Source: openblockchains/awesome-blockchains/blockchain.js)

Yes, that’s it.

Code, A Blockchain in JavaScript in 20 Lines! A Blockchain is a Data Structure (Cont.)

Let’s add two helpers (first, next) for building (“mining”) blocks.

class Block {
  ...
  static first( data="Genesis" ) {    // create genesis (big bang! first) block
    // uses index zero (0) and arbitrary previousHash ("0")
    return new Block( 0, data, "0" )
  }

  static next( previous, data="Transaction Data..." ) {
    return new Block( previous.index+1, data, previous.hash )
  }
}

(Source: openblockchains/awesome-blockchains/blockchain.js)

Let’s get started - build a blockchain a block at a time!

b0 = Block.first( "Genesis" )
b1 = Block.next( b0, "Transaction Data..." )
b2 = Block.next( b1, "Transaction Data......" )
b3 = Block.next( b2, "More Transaction Data..." )

blockchain = [b0, b1, b2, b3]

console.log( blockchain )

Code, A Blockchain in JavaScript in 20 Lines! A Blockchain is a Data Structure (Cont.)

Wait, so a blockchain is just a linked list?

No. A linked list is only required to have a reference to the previous element, a block must have an identifier depending on the previous block’s identifier, meaning that you cannot replace a block without recomputing every single block that comes after. In this implementation that happens as the previous digest is input in the calc_hash method.

will log something like:

[ Block {
      index: 0,
      timestamp: 2017-09-18T08:25:54,
      data: 'Genesis',
      previousHash: '0',
      hash:         'c396de4c03ddb5275661982adc75ce5fc5905d2a2457d1266c74436c1f3c50f1' },
    Block {
      index: 1,
      timestamp: 2017-09-18T08:25:54,
      data: 'Transaction Data...',
      previousHash: 'c396de4c03ddb5275661982adc75ce5fc5905d2a2457d1266c74436c1f3c50f1',
      hash:         '493131e09c069645c82795c96e4715cea0f5558be514b5096d853a5b9899154a' },
    Block {
      index: 2,
      timestamp: 2017-09-18T08:25:54,
      data: 'Transaction Data......',
      previousHash: '493131e09c069645c82795c96e4715cea0f5558be514b5096d853a5b9899154a',
      hash:         '97aa3cb5052615d60ff8e6b41bef606562588c4874f011970ac2f218e2f0f4a8' },
    Block {
      index: 3,
      timestamp: 2017-09-18T08:25:54,
      data: 'More Transaction Data...',
      previousHash: '97aa3cb5052615d60ff8e6b41bef606562588c4874f011970ac2f218e2f0f4a8',
      hash:         'e10e020f832e46c2b60e1c3c0412bd370b2fde5f0f782c16eb87d0313ea0d3a3' } ]

What about Proof-of-Work? What about Consensus?

Making (Hash) Mining a Lottery - Find the Lucky Number

calcHash() {
  var sha = SHA256.create()
  sha.update( this.index.toString() +
              this.timestamp.toString() +
              this.data +
              this.previousHash )
  return sha.hex()
}

The computer (node) in the blockchain network that computes the next block with a valid hash wins the lottery?

For adding a block to the chain you get a reward! You get 25 Bitcoin! (†)

Bitcoin adds a block every ten minutes.

(†) The reward gets halfed. In Sep’17 you’ll get 12.5 Bitcoin.

What about Proof-of-Work? What about Consensus? (Cont.)

Random SHA256 hash #1: c396de4c03ddb5275661982adc75ce5fc5905d2a2457d1266c74436c1f3c50f1

Random SHA256 hash #2: 493131e09c069645c82795c96e4715cea0f5558be514b5096d853a5b9899154a

Triva Q: What’s SHA256?

(A) Still Hacking Anyway
(B) Secure Hash Algorithm
© Sweet Home Austria
(D) Super High Aperture

What about Proof-of-Work? What about Consensus? (Cont.)

A: SHA256 == Secure Hash Algorithms 256 Bits

Trivia: Designed by the National Security Agency (NSA) of the United States of America (USA).

Secure == Random e.g. Change one Letter and the Hash will Change Completely

Making (Hash) Mining a Lottery - Find the Lucky Number

Find a hash that starts with ten leading zeros e.g.

0000000000069645c82795c96e4715cea0f5558be514b5096d853a5b9899154a

Hard to compute! Easy to check / validate.

What about Proof-of-Work? What about Consensus? (Cont.)

Making (Hash) Mining a Lottery - Find the Lucky Number (Nonce)

computeHashWithProofOfWork( difficulty="00" ) {
    var nonce = 0
    while( true ) {
      var hash = this.calcHashWithNonce( nonce )
      if( hash.startsWith( difficulty ))
        return nonce, hash    // bingo! proof of work if hash starts with leading zeros (00)
      else
        nonce += 1            // keep trying (and trying and trying)
    }
}

calcHashWithNonce( nonce=0 ) {
    var sha = SHA256.create()
    sha.update( nonce.toString() +
                this.index.toString() +
                this.timestamp.toString() +
                this.data +
                this.previousHash )
    return sha.hex()
}

(Source: awesome-blockchains/blockchain_with_proof_of_work.js)

The World’s Worst Database - Bitcoin Blockchain Mining

Uses approximately the same amount of electricity as could power an average American household for a day per transaction
Supports 3 transactions / second across a global network with millions of CPUs/purpose-built ASICs
Takes over 10 minutes to “commit” a transaction
Doesn’t acknowledge accepted writes: requires you read your writes, but at any given time you may be on a blockchain fork, meaning your write might not actually make it into the “winning” fork of the blockchain (and no, just making it into the mempool doesn’t count). In other words: “blockchain technology” cannot by definition tell you if a given write is ever accepted/committed except by reading it out of the blockchain itself (and even then)
Can only be used as a transaction ledger denominated in a single currency, or to store/timestamp a maximum of 80 bytes per transaction

(Source: Tony Arcieri - On the dangers of a blockchain monoculture)

Tulips on the Blockchain! Adding Transactions

Learn by Example from the Real World (Anno 1637) - Buy! Sell! Hold! Enjoy the Beauty of Admiral of Admirals, Semper Augustus and More.

Transactions (Hyper) Ledger Book

From	To	What	Qty
Dutchgrown (†)	Vincent	Tulip Bloemendaal Sunset	10
Keukenhof (†)	Anne	Tulip Semper Augustus	7

Flowers (†)	Ruben	Tulip Admiral van Eijck	5
Vicent	Anne	Tulip Bloemendaal Sunset	3
Anne	Julia	Tulip Semper Augustus	1
Julia	Luuk	Tulip Semper Augustus	1

Bloom & Blossom (†)	Daisy	Tulip Admiral of Admirals	8
Vincent	Max	Tulip Bloemendaal Sunset	2
Anne	Martijn	Tulip Semper Augustus	2
Ruben	Julia	Tulip Admiral van Eijck	2

Teleflora (†)	Max	Tulip Red Impression	11
Anne	Naomi	Tulip Bloemendaal Sunset	1
Daisy	Vincent	Tulip Admiral of Admirals	3
Julia	Mina	Tulip Admiral van Eijck	1

Max	Isabel	Tulip Red Impression	2

(†): Grower Transaction - New Tulips on the Market!

(Source: openblockchains/tulips)

Tulips on the Blockchain! Adding Transactions (Cont.)

Quotes - Blockchains are the next Internets / Tulips

People who compare digital tokens to tulips are essentially saying digital tokens are a bubble backed by nothing but pure hype and speculation.

What they fail to understand is that tulips come from dirt, not a blockchain.

And as we all know, blockchain is possibly the best technological innovation since the internet. It will have a tremendous impact on global business and society in general. – TulipToken

Tulips on the Blockchain! Adding Transactions (Cont.)

let b0 = Block.first(
        { from: "Dutchgrown", to: "Vincent", what: "Tulip Bloemendaal Sunset", qty: 10 },
        { from: "Keukenhof",  to: "Anne",    what: "Tulip Semper Augustus",    qty: 7  } )

let b1 = Block.next( b0,
        { from: "Flowers", to: "Ruben", what: "Tulip Admiral van Eijck",  qty: 5 },
        { from: "Vicent",  to: "Anne",  what: "Tulip Bloemendaal Sunset", qty: 3 },
        { from: "Anne",    to: "Julia", what: "Tulip Semper Augustus",    qty: 1 },
        { from: "Julia",   to: "Luuk",  what: "Tulip Semper Augustus",    qty: 1 } )

let b2 = Block.next( b1,
        { from: "Bloom & Blossom", to: "Daisy",   what: "Tulip Admiral of Admirals", qty: 8 },
        { from: "Vincent",         to: "Max",     what: "Tulip Bloemendaal Sunset",  qty: 2 },
        { from: "Anne",            to: "Martijn", what: "Tulip Semper Augustus",     qty: 2 },
        { from: "Ruben",           to: "Julia",   what: "Tulip Admiral van Eijck",   qty: 2 } )
...

Tulips on the Blockchain! Adding Transactions (Cont.)

resulting in:

[ Block {
    index:     0,
    timestamp: 1637-09-25 17:39:21,
    data:
     [ { from: 'Dutchgrown', to: 'Vincent',  what: 'Tulip Bloemendaal Sunset', qty: 10 },
       { from: 'Keukenhof',  to: 'Anne',     what: 'Tulip Semper Augustus',    qty: 7 } ],
    previousHash: '0',
    hash:         '7cb2df9eee29ca77c99eb4591a25dcbdfa9609aff2bd3558d1a0fe22acd08a51' },
  Block {
    index:     1,
    timestamp: 1637-09-25 17:49:21,
    data:
     [ { from: 'Flowers',  to: 'Ruben',  what: 'Tulip Admiral van Eijck',   qty: 5 },
       { from: 'Vicent',   to: 'Anne',   what: 'Tulip Bloemendaal Sunset',  qty: 3 },
       { from: 'Anne',     to: 'Julia',  what: 'Tulip Semper Augustus',     qty: 1 },
       { from: 'Julia',    to: 'Luuk',   what: 'Tulip Semper Augustus',     qty: 1 } ],
    previousHash: '7cb2df9eee29ca77c99eb4591a25dcbdfa9609aff2bd3558d1a0fe22acd08a51',
    hash:         'a7464e98290039f467e7abf6699180205f5151e76b57a79b39f43acc39d75660' },
  Block {
    index:     2,
    timestamp: 1637-09-25 17:59:21,
    data:
     [ { from: 'Bloom & Blossom', to: 'Daisy',    what: 'Tulip Admiral of Admirals', qty: 8 },
       { from: 'Vincent',         to: 'Max',      what: 'Tulip Bloemendaal Sunset',  qty: 2 },
       { from: 'Anne',            to: 'Martijn',  what: 'Tulip Semper Augustus',     qty: 2 },
       { from: 'Ruben',           to: 'Julia',    what: 'Tulip Admiral van Eijck',   qty: 2 } ],
    previousHash: 'a7464e98290039f467e7abf6699180205f5151e76b57a79b39f43acc39d75660',
    hash:         'b7e4952f801651c1e14d61d77b869d18268b46c468923089f1da33e3959b56b9' },
  ...
]

What’s Blockchain Lite - JavaScript Edition?

blockchain-lite library / module (npm: blockchain-lite) - build your own blockchain with crypto hashes - revolutionize the world with blockchains, blockchains, blockchains one block at a time

Usage

Let’s get started. Build your own blockchain one block at a time. Example:

const Blocks = require( "blockchain-lite" )

// use basic block
let Block = Blocks.basic

let b0 = Block.first( 'Genesis' )
let b1 = Block.next( b0, 'Transaction Data...' )
let b2 = Block.next( b1, 'Transaction Data......' )
let b3 = Block.next( b2, 'More Transaction Data...' )

let blockchain = [b0, b1, b2, b3]

console.log( blockchain )