metamask-extension/app/scripts/keyrings/simple.js

const EventEmitter = require('events').EventEmitter
const Wallet = require('ethereumjs-wallet')
const ethUtil = require('ethereumjs-util')
const type = 'Simple Key Pair'

module.exports = class SimpleKeyring extends EventEmitter {

  static type() {
    return type
  }

  constructor(opts) {
    super()
    this.type = type
    this.opts = opts || {}
    this.wallets = []
  }

  serialize() {
    return this.wallets.map(w => w.getPrivateKey().toString('hex'))
  }

  deserialize(wallets = []) {
    this.wallets = wallets.map((w) => {
      var b = new Buffer(w, 'hex')
      const wallet = Wallet.fromPrivateKey(b)
      return wallet
    })
  }

  addAccounts(n = 1) {
    var newWallets = []
    for (var i = 0; i < n; i++) {
      newWallets.push(Wallet.generate())
    }
    this.wallets = this.wallets.concat(newWallets)
    return newWallets.map(w => w.getAddress().toString('hex'))
  }

  getAccounts() {
    return this.wallets.map(w => w.getAddress().toString('hex'))
  }

  // tx is an instance of the ethereumjs-transaction class.
  signTransaction(address, tx) {
    const wallet = this.getWalletForAccount(address)
    var privKey = wallet.getPrivateKey()
    tx.sign(privKey)
    return tx
  }

  // For eth_sign, we need to sign transactions:
  signMessage(withAccount, data) {
    const wallet = this.getWalletForAccount(withAccount)
    const message = ethUtil.removeHexPrefix(data)
    var privKey = wallet.getPrivateKey()
    var msgSig = ethUtil.ecsign(new Buffer(message, 'hex'), privKey)
    var rawMsgSig = ethUtil.bufferToHex(concatSig(msgSig.v, msgSig.r, msgSig.s))
    return rawMsgSig
  }

  getWalletForAccount(account) {
    return this.wallets.find(w => w.getAddress().toString('hex') === account)
  }

}

function concatSig (v, r, s) {
  const rSig = ethUtil.fromSigned(r)
  const sSig = ethUtil.fromSigned(s)
  const vSig = ethUtil.bufferToInt(v)
  const rStr = padWithZeroes(ethUtil.toUnsigned(rSig).toString('hex'), 64)
  const sStr = padWithZeroes(ethUtil.toUnsigned(sSig).toString('hex'), 64)
  const vStr = ethUtil.stripHexPrefix(ethUtil.intToHex(vSig))
  return ethUtil.addHexPrefix(rStr.concat(sStr, vStr)).toString('hex')
}

function padWithZeroes (number, length) {
  var myString = '' + number
  while (myString.length < length) {
    myString = '0' + myString
  }
  return myString
}