Blockchain at Heart

Blockchain Is the Most Disruptive Invention Since the Internet (?)

DuckDuckGo Research

• Decentralization
• Smart Contracts
• Mining
• Resources Consumption
• etc.

Nope

The longest running blockchain started in 1995 and is still running strong today. Current hash circled in red. Based on Stuart Haber and W. Scott Stornetta https://t.co/q1VIUvwGUA pic.twitter.com/eGEhqFSl7U

— Ittai Abraham (@ittaia) August 23, 2018

What is it?

A Blockchain,
is a series (a chain)
of structured data (blocks)

• Track the data
• Certify

The Byzantine Fault

Automation

“Smart Contracts”

A Block

{
  index: 1,
  hash: "7A7D12...E62EC2",
  parent: "3A1A1D...684E1E",
  data: [...],
  timestamp: 1548237157237
}

Hash

SHA256({
  index: 1,
  parent: "3A1A1D...684E1E",
  data: [...],
  timestamp: 1548237157237
}) === "7A7D12...E62EC2"

Data

{
  data: [
    {hash:"67c...640", data: ..., timestamp: 1548237157237},
    {hash:"82a...503", data: ..., timestamp: 1548237157252},
  ]
}

A Blockchain

class Blockchain {
  constructor() {
    this.blocks = [{
      hash: "000000",
      index: 0,
      data: null,
      timestamp: Date.now()
    }]
  }
}

Adding a block

class Blockchain {...
  addBlock(data) {
    const block = {
      index: this.blocks.length,
      parent: this.blocks[this.blocks.length -1].hash
      data,
      timestamp: Date.now()
    }
    block.hash = CryptoJS.SHA256(`
      ${block.index};${block.parent};
      ${JSON.stringify(data)};${block.timestamp}
    `)
    return this.blocks.push(block)
  }
}

Adding a transaction

class Blockchain {...
  transaction(data) {
    const transaction = {
      data,
      timestamp: Date.now()
    }
    transaction.hash = CryptoJS.SHA256(`
      ${JSON.stringify(data)};${transaction.timestamp}
    `)
    return transaction
  }
}

In action

const blockchain = new Blockchain

blockchain.addBlock([
  blockchain.transaction({
    id: 2820628...37, name: 'Jane Doe', note: 'Registration'
  })
  blockchain.transaction({
    id: 2820628...37,
    prescription: [{
      name: 'Paracetamol',
      dosage: '3-6/day'
    }]
  })
])

Moaaaar

blockchain.addBlock{[
  blockchain.transaction({
    id: 1940269...51,
    name: 'John Doe',
    note: 'Registration'
  })
]}

[{
  index: 0, hash: "000000", data: null, timestamp: 1548237157237
},{
  index: 1,
  hash: "7A7D12...E62EC2", parent: "000000",
  data: [{
    {hash:"67C...640", data: ..., timestamp: 1548237157237},
    {hash:"82A...503", data: ..., timestamp: 1548237157252}
  }], timestamp: 1548237157237
},{
  index: 2,
  hash: "6DE54C...87FEB7D", parent: "7A7D12...E62EC2",
  data: [{
    {hash:"AE4...953", data: ..., timestamp: 1548237157237}
  }], timestamp: 1548237157237
}]

Adding a client

class Blockchain {
  constructor() {...
    this.users = []
  }

  register(user) {
    const keys = GenKeyPair()
    user.pubKey = keys.pubKey
    this.users.push(user)
    return key.privKey
  }
}

Signing the transaction

class Blockchain {...
  transaction(data, privKey) {...
    transaction.sign = Sign(transaction.hash, privKey)
  }
}

blockchain.transaction({
  id: 1940269...51,
  name: 'John Doe',
  note: 'Registration'
}, Storage.privKey)

Verifying the transaction

class Blockchain {...
  findUserForTransaction(transaction) {
    return this.users.find(user => Verify(transaction.sign, user.pubKey))
  }
  checkTransaction(transaction) {
    return !!findUserForTransaction(transaction)
  }
}

class Blockchain {...
  register(user, privKey) {
    const keys = GenKeyPair()
    user.pubKey = keys.pubKey
    user.pubKey.sign = Sign(keys.pubKey, privKey)
    this.users.push(user)
    return key.privKey
  }
  checkUserKey(pubKey) {
    return !!this.users.find(user => Verify(pubKey.sign, user.pubKey))
  }
  checkTransaction(transaction) {
    const user = findUserForTransaction(transaction)
    return user ? checkUserKey(user.pubKey) : false
  }
}

Control the blocks

class Blockchain {...
  addBlock(data) {
    if (!data.every(this.checkTransaction)) {
      throw
    }
    ...
  }
}

const pharmacy = blockchain.getUser(pharmacyID)

transaction({
  id: 2820628...37,
  prescription: Encrypt(JSON.stringify([{
    name: 'Paracetamol',
    dosage: '3-6/day'
  }]), pharmacy.pubKey)
})

• Broadcast UDP (dgram)
  • Transactions
  • Blocks
  • Metadata
• Disk persistence
• LRU (Least Recently Used) Local Cache

Nakamoto Agreement

class Blockchain {...
  const inc = 5, prefix = Array(inc).fill(0).join('')
  addBlock(data) {...
    while (true) {
      block.nonce = Math.random()
      block.hash = CryptoJS.SHA256(`
        ${block.nonce};${block.index};${block.parent};
        ${JSON.stringify(data)};${block.timestamp}
      `)
      if (block.hash.substr(0, inc) === prefix) {
        this.blocks.push(block); break
      }
    }
  }
}

Smart Contracts

class SmartContract {
  validate (transaction) {
    return true
  }

  exec (transaction) {
    return true
  }
}

At run

class Blockchain {...
  addContract (contract) {
    this.contracts.push(contract)
  }
  addBlock (data, ...) {...
    this.blocks.push(block)
    block.data.forEach(transaction => {
      this.contracts
      .filter(contract => contract.validate(transaction))
      .each(contract => contract.exec(transaction))
    })
  }
}