主要功能
区块链js实现
链条防篡改
交易签名
挖矿

const sha256 = require('crypto-js/sha256')
const EClib = require('elliptic').ec
const ec = new EClib('secp256k1') // curve name
class Transaction {
  constructor (from, to, amount) {
    this.from = from
    this.to = to
    this.amount = amount
  }

  computeHash () {
    return sha256(
      this.from + this.to + this.amount
    ).toString()
  }

  sign (key) { // 私钥
    this.signature = key.sign(this.computeHash(), 'base64').toDER('hex')
  }

  isValid () { // 公钥
    if (this.from === '') {
      return true
    }
    const keyObj = ec.keyFromPublic(this.from, 'hex')
    return keyObj.verify(this.computeHash(), this.signature)
  }
}

class Block {
  constructor (transaction, previousHash) {
    this.transaction = transaction
    this.nonce = 1
    this.timesramp = Date.now()
    this.previousHash = previousHash
    this.hash = this.computeHash()
  }

  computeHash () {
    return sha256(JSON.stringify(this.transaction) + this.previousHash + this.nonce + this.timesramp).toString()
  }

  static getAnswer (difficulty) {
    let answer = ''
    for (let i = 0; i < difficulty; i++) {
      answer += '0'
    }
    return answer
  }

  mine (difficulty) {
    this.validateBlockTransactions()
    while (true) {
      this.hash = this.computeHash()
      if (this.hash.substring(0, difficulty) !== Block.getAnswer(difficulty)) {
        this.nonce += 1
        this.hash = this.computeHash()
      } else {
        break
      }
    }
    return this.hash
  }

  validateBlockTransactions () {
    for (let transaction of this.transaction) {
      if (!transaction.isValid()) {
        console.log('验证失败')
        return false
      }
    }
    return true
  }
}

class Chain {
  constructor (difficulty = 2, minerReward = 50) {
    this.chain = [Chain.bigBang()]
    this.transactionPool = []
    this.minerReward = minerReward
    this.difficulty = difficulty
  }

  static bigBang () {
    return new Block('Genesis Block', '')
  }

  getLastBlockPreviousHash () {
    return this.chain[this.chain.length - 1].hash
  }

  addTransactionToPool (transaction) {
    if (!transaction.isValid()) {
      console.log('验证签名失败')
      return
    }
    this.transactionPool.push(transaction)
  }

  addBlockToChain (newBlock) {
    if (this.verifyPreviousHash()) {
      newBlock.previousHash = this.getLastBlockPreviousHash()
      // newBlock.hash = newBlock.mine(this.difficulty)
      this.chain.push(newBlock)
    }
  }

  mineTransactionPool (minerRewardAddress) {
    const minerRewardTransaction = new Transaction(
      '',
      minerRewardAddress,
      this.minerReward
    )
    this.transactionPool.push(minerRewardTransaction)

    const newBlock = new Block(
      this.transactionPool,
      this.getLastBlockPreviousHash()
    )
    newBlock.mine(this.difficulty)
    this.addBlockToChain(newBlock)
    this.transactionPool = []
  }

  verifyPreviousHash () {
    for (let i = 0; i < this.chain.length; i++) {
      const nowStock = this.chain[i]
      if (i === 0) {
        if (nowStock.hash !== nowStock.computeHash()) {
          console.log('第一个数据被篡改')
          return false
        }
      } else {
        const previousStock = this.chain[i - 1]
        if (nowStock.hash !== nowStock.computeHash() || nowStock.previousHash !== previousStock.hash) {
          console.log('后面的数据被篡改')
          return false
        }
      }
    }
    return true
  }
}

const chain = new Chain()
const keyPairSender = ec.genKeyPair()
const privateKeySender = keyPairSender.getPublic('hex')
const publickKeySender = keyPairSender.getPublic('hex')

const keyPairReceiver = ec.genKeyPair()
const privateKeyReceiver = keyPairSender.getPublic('hex')
const publickKeyReceiver = keyPairSender.getPublic('hex')

const t1 = new Transaction(keyPairSender, keyPairReceiver, 10)
t1.sign(keyPairSender)
console.log(t1)
console.log(t1.isValid())
// const t2 = new Transaction(keyPairSender, keyPairReceiver, 50)
chain.addTransactionToPool(t1)
// chain.addTransactionToPool(t2)

chain.mineTransactionPool(keyPairSender)
console.log(chain.chain[1].transaction)
console.log(chain)