Implement HMAC support in lib/crypto.

lib/crypto/hmac.dart

Index: lib/crypto/hmac.dart
diff --git a/lib/crypto/hmac.dart b/lib/crypto/hmac.dart
new file mode 100644
index 0000000000000000000000000000000000000000..923d281205b23d42a9d0c9ea5e054309aa35b561
--- /dev/null
+++ b/lib/crypto/hmac.dart
@@ -0,0 +1,55 @@
+// 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();
+    }
+
+    // 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;
+}