bitcoinjs-lib/src/message.js

/// Implements Bitcoin's feature for signing arbitrary messages.

var SHA256 = require('crypto-js/sha256');
var ecdsa = require('./ecdsa');
var convert = require('./convert');

var Message = {};

Message.magicPrefix = "Bitcoin Signed Message:\n";

Message.makeMagicMessage = function (message) {
  var magicBytes = convert.stringToBytes(Message.magicPrefix);
  var messageBytes = convert.stringToBytes(message);

  var buffer = [];
  buffer = buffer.concat(convert.numToVarInt(magicBytes.length));
  buffer = buffer.concat(magicBytes);
  buffer = buffer.concat(convert.numToVarInt(messageBytes.length));
  buffer = buffer.concat(messageBytes);

  return buffer;
};

Message.getHash = function (message) {
  var buffer = Message.makeMagicMessage(message);
  return convert.wordArrayToBytes(SHA256(SHA256(convert.bytesToWordArray(buffer))));
};

Message.signMessage = function (key, message) {
  var hash = Message.getHash(message);

  var sig = key.sign(hash);

  var obj = ecdsa.parseSig(sig);

  var i = ecdsa.calcPubkeyRecoveryParam(key, obj.r, obj.s, hash);

  i += 27;
  if (key.compressed) i += 4;

  var rBa = obj.r.toByteArrayUnsigned();
  var sBa = obj.s.toByteArrayUnsigned();

  // Pad to 32 bytes per value
  while (rBa.length < 32) rBa.unshift(0);
  while (sBa.length < 32) sBa.unshift(0);

  sig = [i].concat(rBa).concat(sBa);

  return convert.bytesToHex(sig);
};

Message.verifyMessage = function (address, sig, message) {
  sig = convert.hexToBytes(sig);
  sig = ecdsa.parseSigCompact(sig);

  var hash = Message.getHash(message);

  var isCompressed = !!(sig.i & 4);
  var pubKey = ecdsa.recoverPubKey(sig.r, sig.s, hash, sig.i);
  pubKey.compressed = isCompressed;

  var expectedAddress = pubKey.getAddress().toString();

  return (address === expectedAddress);
};

module.exports = Message;