Added EC Point multiplication to browser/Point.js

lib/Armory.js

@@ -0,0 +1,41 @@
+var Point = require('./browser/Point'),
+  twoSha256 = require('../util').twoSha256,
+  BigInteger = require('../browser/vendor-bundle.js').BigInteger;
+
+// TODO: use native modules instead of browser libraries
+
+/**
+ * For now, this class can only supports derivation from public key
+ * It doesn't support private key derivation (TODO).
+ *
+ * @example examples/Armory.js
+ */
+function Armory (chaincode, pubkey) {
+  this.chaincode = new Buffer(chaincode, 'hex');
+  this.pubkey = new Buffer(pubkey, 'hex');
+}
+
+Armory.prototype.generatePubKey = function () {
+  var pubKey = this.pubkey;
+  var chainCode = this.chaincode;
+  var chainXor = twoSha256(pubKey);
+
+  for (var i = 0; i < 32; i++)
+    chainXor[i] ^= chainCode[i];
+
+  var A = new BigInteger(chainXor.toString('hex'), 16);
+
+  var pt = Point.fromUncompressedPubKey(pubKey);
+  pt = Point.multiply(pt, A);
+
+  var new_pubkey = pt.toUncompressedPubKey();
+
+  return new_pubkey;
+};
+
+Armory.prototype.next = function () {
+  var next_pubkey = this.generatePubKey();
+  return new Armory(this.chaincode, next_pubkey);
+};
+
+module.exports = Armory;

lib/browser/Point.js

@@ -48,6 +48,30 @@ Point.add = function(p1, p2) {
   return point;
 };
 
+Point.multiply = function(p1, A) {
+  var ecparams = getSECCurveByName('secp256k1');
+
+  var p1xhex = p1.x.toBuffer({size: 32}).toString('hex');
+  var p1x = new BigInteger(p1xhex, 16);
+  var p1yhex = p1.y.toBuffer({size: 32}).toString('hex');
+  var p1y = new BigInteger(p1yhex, 16);
+  var p1px = new ECFieldElementFp(ecparams.getCurve().getQ(), p1x);
+  var p1py = new ECFieldElementFp(ecparams.getCurve().getQ(), p1y);
+  var p1p = new ECPointFp(ecparams.getCurve(), p1px, p1py);
+
+  var p = p1p.multiply(A);
+
+  var point = new Point();
+  var pointxbuf = new Buffer(p.getX().toBigInteger().toByteArrayUnsigned());
+  point.x = bignum.fromBuffer(pointxbuf, {size: pointxbuf.length});
+  assert(pointxbuf.length <= 32);
+  var pointybuf = new Buffer(p.getY().toBigInteger().toByteArrayUnsigned());
+  assert(pointybuf.length <= 32);
+  point.y = bignum.fromBuffer(pointybuf, {size: pointybuf.length});
+
+  return point;
+};
+
 //convert the public key of a Key into a Point
 Point.fromUncompressedPubKey = function(pubkey) {
   var point = new Point();