From d1a570135d6b9ed75914c4e58963bcfd82a492c6 Mon Sep 17 00:00:00 2001
From: "Ryan X. Charles" <ryan@bitpay.com>
Date: Tue, 2 Sep 2014 15:25:16 -0700
Subject: [PATCH] getSharedKeypair & getReceivePubkey

---
 lib/expmt/stealthaddress.js | 21 +++++++++++++++++++--
 test/stealthaddress.js      | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/lib/expmt/stealthaddress.js b/lib/expmt/stealthaddress.js
index 9f6e3f987..0d8212853 100644
--- a/lib/expmt/stealthaddress.js
+++ b/lib/expmt/stealthaddress.js
@@ -1,6 +1,7 @@
 var Stealthkey = require('./stealthkey');
 var Base58check = require('../base58check');
 var Pubkey = require('../pubkey');
+var KDF = require('../kdf');
 
 var StealthAddress = function StealthAddress(addrstr) {
   if (!(this instanceof StealthAddress))
@@ -27,8 +28,8 @@ StealthAddress.prototype.set = function(obj) {
 
 StealthAddress.prototype.fromStealthkey = function(stealthkey) {
   this.set({
-    payloadPubkey: stealthkey.payloadPubkey,
-    scanPubkey: stealthkey.scanPubkey
+    payloadPubkey: stealthkey.payloadKeypair.pubkey,
+    scanPubkey: stealthkey.scanKeypair.pubkey
   });
   return this;
 };
@@ -53,6 +54,22 @@ StealthAddress.prototype.fromString = function(str) {
   return this;
 };
 
+StealthAddress.prototype.getSharedKeypair = function(senderKeypair) {
+  var sharedSecretPoint = this.scanPubkey.point.mul(senderKeypair.privkey.bn);
+  var sharedSecretPubkey = Pubkey(sharedSecretPoint);
+  var buf = sharedSecretPubkey.toDER(true);
+  var sharedKeypair = KDF.sha256hmac2keypair(buf);
+
+  return sharedKeypair;
+};
+
+StealthAddress.prototype.getReceivePubkey = function(senderKeypair) {
+  var sharedKeypair = this.getSharedKeypair(senderKeypair);
+  var pubkey = Pubkey(this.payloadPubkey.point.add(sharedKeypair.pubkey.point));
+
+  return pubkey;
+};
+
 StealthAddress.prototype.toBuffer = function() {
   var pBuf = this.payloadPubkey.toDER(true);
   var sBuf = this.scanPubkey.toDER(true);
diff --git a/test/stealthaddress.js b/test/stealthaddress.js
index 872b1de0a..e4962be62 100644
--- a/test/stealthaddress.js
+++ b/test/stealthaddress.js
@@ -61,6 +61,43 @@ describe('StealthAddress', function() {
 
   });
 
+  describe('#getSharedKeypair', function() {
+
+    it('should return a key', function() {
+      var sa = new StealthAddress();
+      sa.payloadPubkey = stealthkey.payloadKeypair.pubkey;
+      sa.scanPubkey = stealthkey.scanKeypair.pubkey;
+      var key = sa.getSharedKeypair(senderKeypair);
+      (key instanceof Keypair).should.equal(true);
+    });
+
+    it('should return the same key as Stealthkey.prototype.getSharedKeypairAsReceiver', function() {
+      var sa = new StealthAddress();
+      sa.payloadPubkey = stealthkey.payloadKeypair.pubkey;
+      sa.scanPubkey = stealthkey.scanKeypair.pubkey;
+      var key = sa.getSharedKeypair(senderKeypair);
+
+      var key2 = stealthkey.getSharedKeypairAsReceiver(senderKeypair.pubkey);
+      key.toString().should.equal(key2.toString());
+    });
+
+  });
+
+  describe('#getReceivePubkey', function() {
+    
+    it('should return a pubkey', function() {
+      var pubkey = StealthAddress().fromStealthkey(stealthkey).getReceivePubkey(senderKeypair);
+      (pubkey instanceof Pubkey).should.equal(true);
+    });
+
+    it('should return the same pubkey as getReceivePubkeyAsReceiver', function() {
+      var pubkey = StealthAddress().fromStealthkey(stealthkey).getReceivePubkey(senderKeypair);
+      var pubkey2 = stealthkey.getReceivePubkeyAsReceiver(senderKeypair.pubkey);
+      pubkey2.toString().should.equal(pubkey.toString());
+    });
+
+  });
+
   describe('#toBuffer', function() {
     
     it('should return this known address buffer', function() {