index.js

var aes = require('browserify-aes')
var assert = require('assert')
var Buffer = require('safe-buffer').Buffer
var bs58check = require('bs58check')
var createHash = require('create-hash')
var scrypt = require('scryptsy-async')
var xor = require('buffer-xor/inplace')

var ecurve = require('ecurve')
var curve = ecurve.getCurveByName('secp256k1')

var bitcoin = require('bitcoinjs-lib')
var { addressFunctionP2PKH } = require('coinid-address-functions');

var BigInteger = require('bigi')

// constants
var SCRYPT_PARAMS = {
  N: 16384, // specified by BIP38
  r: 8,
  p: 8
}
var NULL = Buffer.alloc(0)

function hash160 (buffer) {
  return createHash('rmd160').update(
    createHash('sha256').update(buffer).digest()
  ).digest()
}

function hash256 (buffer) {
  return createHash('sha256').update(
    createHash('sha256').update(buffer).digest()
  ).digest()
}

function getAddress (d, compressed, network) {
  const node = new bitcoin.ECPair(d, null, {
    compressed,
    network
  });

  const address = addressFunctionP2PKH(node);
  return address;
}

async function encryptRaw (buffer, compressed, passphrase, network, progressCallback, scryptParams) {
  if (buffer.length !== 32) throw new Error('Invalid private key length')
  scryptParams = scryptParams || SCRYPT_PARAMS

  var d = BigInteger.fromBuffer(buffer)
  var address = getAddress(d, compressed, network)
  var secret = Buffer.from(passphrase, 'utf8')
  var salt = hash256(address).slice(0, 4)

  var N = scryptParams.N
  var r = scryptParams.r
  var p = scryptParams.p

  var scryptBuf = await scrypt(secret, salt, N, r, p, 64, progressCallback)
  var derivedHalf1 = scryptBuf.slice(0, 32)
  var derivedHalf2 = scryptBuf.slice(32, 64)

  var xorBuf = xor(derivedHalf1, buffer)
  var cipher = aes.createCipheriv('aes-256-ecb', derivedHalf2, NULL)
  cipher.setAutoPadding(false)
  cipher.end(xorBuf)

  var cipherText = cipher.read()

  // 0x01 | 0x42 | flagByte | salt (4) | cipherText (32)
  var result = Buffer.allocUnsafe(7 + 32)
  result.writeUInt8(0x01, 0)
  result.writeUInt8(0x42, 1)
  result.writeUInt8(compressed ? 0xe0 : 0xc0, 2)
  salt.copy(result, 3)
  cipherText.copy(result, 7)

  return result
}

async function encrypt (buffer, compressed, passphrase, network, progressCallback, scryptParams) {
  return bs58check.encode(await encryptRaw(buffer, compressed, passphrase, network, progressCallback, scryptParams))
}

// some of the techniques borrowed from: https://github.com/pointbiz/bitaddress.org
async function decryptRaw (buffer, passphrase, network, progressCallback, scryptParams) {
  // 39 bytes: 2 bytes prefix, 37 bytes payload
  if (buffer.length !== 39) throw new Error('Invalid BIP38 data length')
  if (buffer.readUInt8(0) !== 0x01) throw new Error('Invalid BIP38 prefix')
  scryptParams = scryptParams || SCRYPT_PARAMS

  // check if BIP38 EC multiply
  var type = buffer.readUInt8(1)
  if (type === 0x43) return decryptECMult(buffer, passphrase, network, progressCallback, scryptParams)
  if (type !== 0x42) throw new Error('Invalid BIP38 type')

  passphrase = Buffer.from(passphrase, 'utf8')

  var flagByte = buffer.readUInt8(2)
  var compressed = flagByte === 0xe0
  if (!compressed && flagByte !== 0xc0) throw new Error('Invalid BIP38 compression flag')

  var N = scryptParams.N
  var r = scryptParams.r
  var p = scryptParams.p

  var salt = buffer.slice(3, 7)
  var scryptBuf = await scrypt(passphrase, salt, N, r, p, 64, progressCallback)
  var derivedHalf1 = scryptBuf.slice(0, 32)
  var derivedHalf2 = scryptBuf.slice(32, 64)

  var privKeyBuf = buffer.slice(7, 7 + 32)
  var decipher = aes.createDecipheriv('aes-256-ecb', derivedHalf2, NULL)
  decipher.setAutoPadding(false)
  decipher.end(privKeyBuf)

  var plainText = decipher.read()
  var privateKey = xor(derivedHalf1, plainText)

  // verify salt matches address
  var d = BigInteger.fromBuffer(privateKey)
  var address = getAddress(d, compressed, network)
  var checksum = hash256(address).slice(0, 4)
  assert.deepEqual(salt, checksum)

  return {
    privateKey: privateKey,
    compressed: compressed
  }
}

function decrypt (string, passphrase, network, progressCallback, scryptParams) {
  return decryptRaw(bs58check.decode(string), passphrase, network, progressCallback, scryptParams)
}

async function decryptECMult (buffer, passphrase, network, progressCallback, scryptParams) {
  passphrase = Buffer.from(passphrase, 'utf8')
  buffer = buffer.slice(1) // FIXME: we can avoid this
  scryptParams = scryptParams || SCRYPT_PARAMS

  var flag = buffer.readUInt8(1)
  var compressed = (flag & 0x20) !== 0
  var hasLotSeq = (flag & 0x04) !== 0

  assert.equal((flag & 0x24), flag, 'Invalid private key.')

  var addressHash = buffer.slice(2, 6)

  var ownerEntropy = buffer.slice(6, 14)
  var ownerSalt

  // 4 bytes ownerSalt if 4 bytes lot/sequence
  if (hasLotSeq) {
    ownerSalt = ownerEntropy.slice(0, 4)

  // else, 8 bytes ownerSalt
  } else {
    ownerSalt = ownerEntropy
  }

  var encryptedPart1 = buffer.slice(14, 22) // First 8 bytes
  var encryptedPart2 = buffer.slice(22, 38) // 16 bytes

  var N = scryptParams.N
  var r = scryptParams.r
  var p = scryptParams.p
  var preFactor = await scrypt(passphrase, ownerSalt, N, r, p, 32, progressCallback)

  var passFactor
  if (hasLotSeq) {
    var hashTarget = Buffer.concat([preFactor, ownerEntropy])
    passFactor = hash256(hashTarget)
  } else {
    passFactor = preFactor
  }

  var passInt = BigInteger.fromBuffer(passFactor)
  var passPoint = curve.G.multiply(passInt).getEncoded(true)

  var seedBPass = await scrypt(passPoint, Buffer.concat([addressHash, ownerEntropy]), 1024, 1, 1, 64)
  var derivedHalf1 = seedBPass.slice(0, 32)
  var derivedHalf2 = seedBPass.slice(32, 64)

  var decipher = aes.createDecipheriv('aes-256-ecb', derivedHalf2, Buffer.alloc(0))
  decipher.setAutoPadding(false)
  decipher.end(encryptedPart2)

  var decryptedPart2 = decipher.read()
  var tmp = xor(decryptedPart2, derivedHalf1.slice(16, 32))
  var seedBPart2 = tmp.slice(8, 16)

  var decipher2 = aes.createDecipheriv('aes-256-ecb', derivedHalf2, Buffer.alloc(0))
  decipher2.setAutoPadding(false)
  decipher2.write(encryptedPart1) // first 8 bytes
  decipher2.end(tmp.slice(0, 8)) // last 8 bytes

  var seedBPart1 = xor(decipher2.read(), derivedHalf1.slice(0, 16))
  var seedB = Buffer.concat([seedBPart1, seedBPart2], 24)
  var factorB = BigInteger.fromBuffer(hash256(seedB))

  // d = passFactor * factorB (mod n)
  var d = passInt.multiply(factorB).mod(curve.n)

  // assert checksum
  var address = getAddress(d, compressed, network)
  var checksum = hash256(address).slice(0, 4)
  assert.deepEqual(addressHash, checksum)

  return {
    privateKey: d.toBuffer(32),
    compressed: compressed
  }
}

function verify (string, address) {
  var decoded = bs58check.decodeUnsafe(string)
  if (!decoded) return false

  if (decoded.length !== 39) return false
  if (decoded.readUInt8(0) !== 0x01) return false

  var type = decoded.readUInt8(1)
  var flag = decoded.readUInt8(2)

  // encrypted WIF
  if (type === 0x42) {
    if (flag !== 0xc0 && flag !== 0xe0) return false

    // if address is supplied we also verify with that.
    if(address) {
      var salt = decoded.slice(3, 7)
      var checksum = hash256(address).slice(0, 4);

      try {
        assert.deepEqual(salt, checksum);
      } catch(err) {
        return false;
      }
    }

  // EC mult
  } else if (type === 0x43) {
    if ((flag & ~0x24)) return false
  } else {
    return false
  }

  return true
}

module.exports = {
  decrypt: decrypt,
  decryptECMult: decryptECMult,
  decryptRaw: decryptRaw,
  encrypt: encrypt,
  encryptRaw: encryptRaw,
  verify: verify
}