From a4393c0657667e6e647fe3068724cb7d52ad08bc Mon Sep 17 00:00:00 2001
From: "Ryan X. Charles" <ryan@bitpay.com>
Date: Sun, 23 Mar 2014 15:12:52 -0700
Subject: [PATCH] update BIP32 to be able to derive pubkeys

...using the new addCompressed interface in Key.js
---
 BIP32.js           | 36 ++++++++++++++++++++++++++++--------
 test/test.BIP32.js |  9 +++++++++
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/BIP32.js b/BIP32.js
index 6bfc60d53..dac4c33d2 100644
--- a/BIP32.js
+++ b/BIP32.js
@@ -7,7 +7,7 @@ var crypto = require('crypto');
 var networks = require('./networks');
 
 var secp256k1_n = new bignum("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141", 16);
-var secp256k1_G = new bignum("79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798", 16); //x coordinate
+var secp256k1_Gx = new bignum("79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798", 16);
 
 var BIP32 = function(bytes) {
   if (bytes == 'mainnet' || bytes == 'livenet')
@@ -266,17 +266,37 @@ BIP32.prototype.derive_child = function(i) {
     var ir = hash.slice(32, 64);
 
     // Ki = (IL + kpar)*G = IL*G + Kpar
-    var pub = new bignum(this.eckey.public, {size: 32});
-    var k = secp256k1_G.mul(il).add(pub);
+    var key = new Key();
+    key.private = il.toBuffer({size: 32});
+    key.regenerateSync();
+    key.compressed = false;
+    var oldkey = new Key();
+    oldkey.public = this.eckey.public;
+    oldkey.compressed = false;
+    var newpub = Key.addUncompressed(key.public, oldkey.public);
 
-    //compressed pubkey must start with 0x02 just like compressed G
-    var kbuf = Buffer.concat([new Buffer(0x02), k.toBuffer({size: 32})]);
+    var eckey = new Key();
+    eckey.compressed = false;
+    eckey.public = newpub;
+    if (eckey.public === null) {
+      console.log('invalid public key');
+      return this.derive_child(i+1);
+    }
+    eckey.compressed = true;
+
+/*
+    if (k.gt(secp256k1_n))
+      return this.derive_child(i+1);
+*/
 
     ret = new BIP32();
-    ret.chain_code  = new Buffer(ir);
+    ret.chain_code = new Buffer(ir);
 
-    ret.eckey = new Key();
-    ret.eckey.public = kbuf;
+    var eckey = new Key();
+    eckey.compressed = false;
+    eckey.public = newpub; 
+    eckey.compressed = true;
+    ret.eckey = eckey;
     ret.has_private_key = false;
   }
 
diff --git a/test/test.BIP32.js b/test/test.BIP32.js
index 95d7ae081..8ed1148a0 100644
--- a/test/test.BIP32.js
+++ b/test/test.BIP32.js
@@ -93,6 +93,15 @@ describe('BIP32', function() {
     child.extended_public_key_string().should.equal(vector1_m0h1_public);
   });
 
+  it("should get m/0'/1 ext. public key from m/0' public key from test vector 1", function() {
+    var bip32 = new BIP32(vector1_m_private);
+    var child = bip32.derive("m/0'");
+    var child_pub = new BIP32(child.extended_public_key_string());
+    var child2 = child_pub.derive("m/1");
+    should.exist(child2);
+    child2.extended_public_key_string().should.equal(vector1_m0h1_public);
+  });
+
   it("should get m/0'/1/2h ext. private key from test vector 1", function() {
     var bip32 = new BIP32(vector1_m_private);
     var child = bip32.derive("m/0'/1/2'");