diff --git a/lib/expmt/cbc.js b/lib/expmt/cbc.js
index bc4f06081..cf95d858f 100644
--- a/lib/expmt/cbc.js
+++ b/lib/expmt/cbc.js
@@ -1,6 +1,11 @@
 var Random = require('../random');
 
-var CBC = function CBC() {
+var CBC = function CBC(blockcipherf, keybuf, ivbuf) {
+  if (!(this instanceof CBC))
+    return new CBC(blockcipherf, keybuf, ivbuf);
+  this.blockcipherf = blockcipherf;
+  this.keybuf = keybuf;
+  this.ivbuf = ivbuf;
 };
 
 CBC.pkcs7pad = function(buf, blocksize) {
@@ -11,4 +16,17 @@ CBC.pkcs7pad = function(buf, blocksize) {
   return Buffer.concat([buf, pad]);
 };
 
+CBC.xorbufs = function(buf1, buf2) {
+  if (buf1.length !== buf2.length)
+    throw new Error('bufs must have the same length');
+
+  var buf = new Buffer(buf1.length);
+
+  for (var i = 0; i < buf1.length; i++) {
+    buf[i] = buf1[i] ^ buf2[i];
+  }
+
+  return buf;
+};
+
 module.exports = CBC;
diff --git a/test/test.cbc.js b/test/test.cbc.js
index e662feb2f..2489131fe 100644
--- a/test/test.cbc.js
+++ b/test/test.cbc.js
@@ -2,6 +2,16 @@ var should = require('chai').should();
 var CBC = require('../lib/expmt/cbc');
 
 describe('CBC', function() {
+
+  it('should return a new CBC', function() {
+    var cbc = new CBC();
+    should.exist(cbc);
+  })
+
+  it('should return a new CBC when called without "new"', function() {
+    var cbc = new CBC();
+    should.exist(cbc);
+  });
   
   describe('@pkcs7pad', function() {
     
@@ -18,4 +28,22 @@ describe('CBC', function() {
 
   });
 
+  describe('@xorbufs', function() {
+    
+    it('should xor 1 and 0', function() {
+      var buf1 = new Buffer([1]);
+      var buf2 = new Buffer([0]);
+      var buf = CBC.xorbufs(buf1, buf2);
+      buf[0].should.equal(1);
+    });
+
+    it('should xor 1 and 1', function() {
+      var buf1 = new Buffer([1]);
+      var buf2 = new Buffer([1]);
+      var buf = CBC.xorbufs(buf1, buf2);
+      buf[0].should.equal(0);
+    });
+
+  });
+
 });