From 73b904ce219ed77934d9c1c5e0bfbe86f3dd4d90 Mon Sep 17 00:00:00 2001
From: "Ryan X. Charles" <ryan@bitpay.com>
Date: Mon, 25 Aug 2014 21:16:33 -0700
Subject: [PATCH] CBC decrypt

---
 lib/expmt/cbc.js | 16 ++++++++++--
 test/test.cbc.js | 67 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+), 2 deletions(-)

diff --git a/lib/expmt/cbc.js b/lib/expmt/cbc.js
index 6835924..f509ba8 100644
--- a/lib/expmt/cbc.js
+++ b/lib/expmt/cbc.js
@@ -43,8 +43,20 @@ CBC.encrypt = function(messagebuf, ivbuf, blockcipher, cipherkeybuf) {
   var blocksize = ivbuf.length * 8;
   var blockbufs = CBC.buf2blockbufs(messagebuf, blocksize);
   var encbufs = CBC.encryptblocks(blockbufs, ivbuf, blockcipher, cipherkeybuf);
-  var enc = Buffer.concat(encbufs);
-  return enc;
+  var encbuf = Buffer.concat(encbufs);
+  return encbuf;
+};
+
+CBC.decrypt = function(encbuf, ivbuf, blockcipher, cipherkeybuf) {
+  var blocksize = ivbuf.length * 8;
+  var bytesize = ivbuf.length;
+  var encbufs = [];
+  for (var i = 0; i < encbuf.length / bytesize; i++) {
+    encbufs.push(encbuf.slice(i * bytesize, i * bytesize + bytesize));
+  }
+  var blockbufs = CBC.decryptblocks(encbufs, ivbuf, blockcipher, cipherkeybuf);
+  var buf = CBC.blockbufs2buf(blockbufs, blocksize);
+  return buf;
 };
 
 CBC.encryptblock = function(blockbuf, ivbuf, blockcipher, cipherkeybuf) {
diff --git a/test/test.cbc.js b/test/test.cbc.js
index c03de0c..03ec539 100644
--- a/test/test.cbc.js
+++ b/test/test.cbc.js
@@ -76,6 +76,73 @@ describe('CBC', function() {
 
   });
   
+  describe('@encrypt', function() {
+
+    it('should return this known value', function() {
+      var messagebuf1 = new Buffer(128 / 8);
+      messagebuf1.fill(0);
+      var messagebuf2 = new Buffer(128 / 8);
+      messagebuf2.fill(0x10);
+      var messagebuf = Buffer.concat([messagebuf1, messagebuf2]);
+      var ivbuf = new Buffer(128 / 8);
+      ivbuf.fill(0x10);
+      var cipherkeybuf = new Buffer(128 / 8);
+      cipherkeybuf.fill(0);
+      var blockcipher = {};
+      blockcipher.encrypt = function(messagebuf, cipherkeybuf) {
+        return messagebuf;
+      };
+      blockcipher.decrypt = function(messagebuf, cipherkeybuf) {
+        return messagebuf;
+      };
+      var encbuf = CBC.encrypt(messagebuf, ivbuf, blockcipher, cipherkeybuf);
+      var buf2 = CBC.decrypt(encbuf, ivbuf, blockcipher, cipherkeybuf);
+    });
+
+    it('should return this shorter known value', function() {
+      var messagebuf1 = new Buffer(128 / 8);
+      messagebuf1.fill(0);
+      var messagebuf2 = new Buffer(120 / 8);
+      messagebuf2.fill(0x10);
+      var messagebuf = Buffer.concat([messagebuf1, messagebuf2]);
+      var ivbuf = new Buffer(128 / 8);
+      ivbuf.fill(0x10);
+      var cipherkeybuf = new Buffer(128 / 8);
+      cipherkeybuf.fill(0);
+      var blockcipher = {};
+      blockcipher.encrypt = function(messagebuf, cipherkeybuf) {
+        return messagebuf;
+      };
+      blockcipher.decrypt = function(messagebuf, cipherkeybuf) {
+        return messagebuf;
+      };
+      var encbuf = CBC.encrypt(messagebuf, ivbuf, blockcipher, cipherkeybuf);
+      var buf2 = CBC.decrypt(encbuf, ivbuf, blockcipher, cipherkeybuf);
+    });
+
+    it('should return this shorter known value', function() {
+      var messagebuf1 = new Buffer(128 / 8);
+      messagebuf1.fill(0);
+      var messagebuf2 = new Buffer(136 / 8);
+      messagebuf2.fill(0x10);
+      var messagebuf = Buffer.concat([messagebuf1, messagebuf2]);
+      var ivbuf = new Buffer(128 / 8);
+      ivbuf.fill(0x10);
+      var cipherkeybuf = new Buffer(128 / 8);
+      cipherkeybuf.fill(0);
+      var blockcipher = {};
+      blockcipher.encrypt = function(messagebuf, cipherkeybuf) {
+        return messagebuf;
+      };
+      blockcipher.decrypt = function(messagebuf, cipherkeybuf) {
+        return messagebuf;
+      };
+      var encbuf = CBC.encrypt(messagebuf, ivbuf, blockcipher, cipherkeybuf);
+      var buf2 = CBC.decrypt(encbuf, ivbuf, blockcipher, cipherkeybuf);
+    });
+
+  });
+  
   describe('@encryptblock', function() {
 
     it('should return this known value', function() {