Implement HMAC support in lib/crypto.

lib/crypto/hmac.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class _HMAC implements HMAC {
+  _HMAC(Hash this._hash, List<int> this._key) : _message = [];
+
+  HMAC update(List<int> data) {
+    _message.addAll(data);
+    return this;
+  }
+
+  List<int> digest() {
+    var blockSize = _hash.blockSize;
+
+    // Hash the key if it is longer than the block size of the hash.
+    if (_key.length > blockSize) {
+      _key = _hash.update(_key).digest();
+      _hash = _hash.newInstance();

[Søren Gjesse, 2012/04/30 09:05:23]

Add and use a reset() method instead? Also as an object implementing Hash is
passed it might be the right thing to do to call reset before using it.

[Mads Ager (google), 2012/04/30 09:37:10]

We explicitly do not want to do that. The reason for not wanting to add reset is
that you can get 'dangling' references to hashes and get weird results. Avoiding
object reuse seems cleaner.

+    }
+
+    // Zero-pad the key until its size is equal to the block size of the hash.
+    if (_key.length < blockSize) {
+      var newKey = new List(blockSize);
+      newKey.setRange(0, _key.length, _key);
+      for (var i = _key.length; i < blockSize; i++) {
+        newKey[i] = 0;
+      }
+      _key = newKey;
+    }
+
+    // Compute inner padding.
+    var padding = new List(blockSize);
+    for (var i = 0; i < blockSize; i++) {
+      padding[i] = 0x36 ^ _key[i];
+    }
+
+    // Inner hash computation.
+    var innerHash = _hash.update(padding).update(_message).digest();
+    _hash = _hash.newInstance();
+
+    // Compute outer padding.
+    for (var i = 0; i < blockSize; i++) {
+      padding[i] = 0x5c ^ _key[i];
+    }
+
+    // Outer hash computation which is the result.
+    return _hash.update(padding).update(innerHash).digest();
+  }
+
+  // HMAC internal state.
+  Hash _hash;
+  List<int> _key;
+  List<int> _message;
+}