electrum_address_generator.js

var ElectrumAddressGenerator = function () {
  var curve = getSECCurveByName("secp256k1"),
      G = curve.getG();
  
  function big_int_hash(n, forChange, pubKey) {
    return BigInteger.fromByteArrayUnsigned(
             Crypto.SHA256(
               Crypto.SHA256(
                 Crypto.charenc.UTF8.stringToBytes(
                   n + ':' + Number(forChange) + ':'
                 ).concat(pubKey.slice(1)),
                 {asBytes: true}
               ),
               {asBytes: true}
             )
           );
  }

  function pt_to_addr(pt) {
    return new Bitcoin.Address(Bitcoin.Util.sha256ripe160(pt.getEncoded()));
  }
  
  return {
    "gen": function (master_pub_key, master_priv_key, n, isChange) {
        var pt_master_pub = ECPointFp.decodeFrom(curve.getCurve(), master_pub_key),
            a = big_int_hash(n, isChange, master_pub_key),
            pt_new_pub = pt_master_pub.add(G.multiply(a));

        if (master_priv_key) {
            var order = curve.getN(),
                new_priv_key = BigInteger.fromByteArrayUnsigned(master_priv_key).add(a).mod(order),
                new_priv_addr = new Bitcoin.Address(new_priv_key.toByteArrayUnsigned());

            new_priv_addr.version = 128;
        }

        return [pt_to_addr(pt_new_pub).toString(), new_priv_addr ? new_priv_addr.toString() : ""];
    },
    
    "priv_to_pub": function (priv_key) {
      var secexp = BigInteger.fromByteArrayUnsigned(priv_key);
      return G.multiply(secexp).getEncoded();
    },
    
    "seed_to_priv": function (str_seed) {
      var first_seed = Crypto.charenc.UTF8.stringToBytes(str_seed),
          seed = first_seed;
          
      for (var i=0; i < 100000; i++) {
        seed = Crypto.SHA256(seed.concat(first_seed), {asBytes: true});
      }
      
      return seed;
    }
  }
};

function ElectrumAddressGenerator_test() {
  var eag = ElectrumAddressGenerator(),
      master_priv_key = eag.seed_to_priv("12345678"),
      master_pub_key = eag.priv_to_pub(master_priv_key);
  
  for (var i=0; i < 10; i++) {
    console.log("Address " + i + ":",  eag.gen(master_pub_key, master_priv_key, i, false));
  }

  for (var i=0; i < 10; i++) {
    console.log("Change address " + i + ":",  eag.gen(master_pub_key, master_priv_key, i, true));
  }
}