Added Electrum.js which allows Electrum style key derivation

examples/ElectrumMPK.js

@@ -0,0 +1,20 @@
+var Key = require('../lib/Key');
+var Address = require('../lib/Address');
+var k = new Key();
+
+//k.public = new Buffer('92eea4d2f5263651db9e3222caded1fd4c89772f79a7c03fb6afc00e9d2c9d2ed9b86c2c95fc1171e49163079dacb7f048b3c509a27a490e1df9e7128362d468', 'hex');
+//k.public = new Buffer('0492eea4d2f5263651db9e3222caded1fd4c89772f79a7c03fb6afc00e9d2c9d2ed9b86c2c95fc1171e49163079dacb7f048b3c509a27a490e1df9e7128362d468', 'hex');
+//k.public = new Buffer('0478d430274f8c5ec1321338151e9f27f4c676a008bdf8638d07c0b6be9ab35c71a1518063243acd4dfe96b66e3f2ec8013c8e072cd09b3834a19f81f659cc3455', 'hex');
+//k.generatePubKey();
+//debugger;
+//console.log(k);
+
+var Electrum = require('../lib/Electrum');
+//92eea4d2f5263651db9e3222caded1fd4c89772f79a7c03fb6afc00e9d2c9d2ed9b86c2c95fc1171e49163079dacb7f048b3c509a27a490e1df9e7128362d468
+var mpk = '92eea4d2f5263651db9e3222caded1fd4c89772f79a7c03fb6afc00e9d2c9d2ed9b86c2c95fc1171e49163079dacb7f048b3c509a27a490e1df9e7128362d468';
+mpk = new Electrum(mpk);
+
+var key1 = mpk.generatePubKey(0);
+var addr1 = Address.fromPubKey(key1);
+
+console.log(addr1.as('base58'));

lib/Electrum.js

@@ -0,0 +1,51 @@
+var Key = require('./Key'),
+  Point = require('./Point'),
+  twoSha256 = require('../util').twoSha256,
+  buffertools = require('buffertools'),
+  bignum = require('bignum');
+
+/**
+ * Pre-BIP32 Electrum public key derivation (electrum <2.0)
+ *
+ * @example examples/ElectrumMPK.js
+ */
+function Electrum (master_public_key) {
+  this.mpk = new Buffer(master_public_key, 'hex');
+}
+
+Electrum.prototype.getSequence = function (for_change, n) {
+  var mode = for_change ? 1 : 0;
+  var buf = Buffer.concat([ new Buffer(n + ':' + mode + ':', 'utf8'), this.mpk ]);
+  return bignum.fromBuffer(twoSha256(buf));
+};
+
+Electrum.prototype.generatePubKey = function (n, for_change) {
+  var x = bignum.fromBuffer(this.mpk.slice(0, 32), { size: 32 });
+  var y = bignum.fromBuffer(this.mpk.slice(32, 64), { size: 32 });
+  var mpk_pt = new Point(x, y);
+
+  var sequence = this.getSequence(false, n);
+  var sequence_key = new Key();
+  sequence_key.private = sequence.toBuffer();
+  sequence_key.regenerateSync();
+
+  var sequence_pt = Point.fromKey(sequence_key);
+
+  pt = Point.add(mpk_pt, sequence_pt);
+
+  var xbuf = pt.x.toBuffer({ size: 32 });
+  var ybuf = pt.y.toBuffer({ size: 32 });
+  var prefix = new Buffer([0x04]);
+
+  var key = new Key();
+  key.compressed = false;
+  key.public = Buffer.concat([prefix, xbuf, ybuf]);
+
+  return key.public;
+};
+
+Electrum.prototype.generateChangePubKey = function (sequence) {
+  return this.generatePubKey(sequence, true);
+};
+
+module.exports = Electrum;

src/eckey.cc

@@ -317,6 +317,7 @@ Key::SetPublic(Local<String> property, Local<Value> value, const AccessorInfo& i
 
   if (!ret) {
     // TODO: Error
+    VException("Invalid public key.");
     return;
   }