Merge pull request #29 from oleganza/master

Deterministic encryption

lib/ecies.js

@@ -33,9 +33,19 @@ ECIES.prototype.publicKey = function(publicKey) {
   return this;
 };
 
-ECIES.prototype.encrypt = function(message) {
+// Encrypts the message (String or Buffer).
+// Optional `ivbuf` contains 16-byte Buffer to be used in AES-CBC.
+// By default, `ivbuf` is computed deterministically from message and private key using HMAC-SHA256.
+// Deterministic IV enables end-to-end test vectors for alternative implementations.
+// Note that identical messages have identical ciphertexts. If your protocol does not include some
+// kind of a sequence identifier inside the message *and* it is important to not allow attacker to learn
+// that message is repeated, then you should use custom IV.
+// For random IV, pass `Random.getRandomBuffer(16)` for the second argument.
+ECIES.prototype.encrypt = function(message, ivbuf) {
   if (!Buffer.isBuffer(message)) message = new Buffer(message);
-  var ivbuf = Random.getRandomBuffer(128 / 8);
+  if (ivbuf === undefined) {
+      ivbuf = Hash.sha256hmac(message, this._privateKey.toBuffer()).slice(0,16);
+  }
 
   var r = this._privateKey.bn;
   var Rpubkey = this._privateKey.publicKey;

test/ecies.js

@@ -53,12 +53,13 @@ describe('ECIES', function() {
     .publicKey(aliceKey.publicKey);
 
   var message = 'attack at dawn';
-  var encrypted = '0339e504d6492b082da96e11e8f039796b06cd4855c101e2492a6f10f3e056a9e7499368e41313fa48f71759d13469c28b0bd6ff03a08b2ae5e6679e848f92db4b26a8ccf9c0b43f16eae6216c36380f70724743fe9053c98d94281aa74c94df40';
+  var encrypted = '0339e504d6492b082da96e11e8f039796b06cd4855c101e2492a6f10f3e056a9e712c732611c6917ab5c57a1926973bc44a1586e94a783f81d05ce72518d9b0a80e2e13c7ff7d1306583f9cc7a48def5b37fbf2d5f294f128472a6e9c78dede5f5';
   var encBuf = new Buffer(encrypted, 'hex');
 
   it('correctly encrypts a message', function() {
-    var encrypted = alice.encrypt(message);
-    Buffer.isBuffer(encrypted).should.equal(true);
+    var ciphertext = alice.encrypt(message);
+    Buffer.isBuffer(ciphertext).should.equal(true);
+    ciphertext.toString('hex').should.equal(encrypted)
   });
 
   it('correctly decrypts a message', function() {