| // 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. |
| |
| part of crypto; |
| |
| /** |
| * Hash-based Message Authentication Code support. |
| * |
| * The [add] method is used to add data to the message. The [digest] and |
| * [close] methods are used to extract the message authentication code. |
| */ |
| // TODO(floitsch): make Hash implement Sink, EventSink or similar. |
| class HMAC { |
| bool _isClosed = false; |
| |
| /** |
| * Create an [HMAC] object from a [Hash] and a key. |
| */ |
| HMAC(Hash this._hash, List<int> this._key) : _message = []; |
| |
| /** |
| * Add a list of bytes to the message. |
| */ |
| void add(List<int> data) { |
| if (_isClosed) throw new StateError("HMAC is closed"); |
| _message.addAll(data); |
| } |
| |
| /** |
| * Extract the message digest as a list of bytes without closing [this]. |
| */ |
| List<int> get digest { |
| var blockSize = _hash.blockSize; |
| |
| // Hash the key if it is longer than the block size of the hash. |
| if (_key.length > blockSize) { |
| _hash = _hash.newInstance(); |
| _hash.add(_key); |
| _key = _hash.close(); |
| } |
| |
| // 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. |
| _hash = _hash.newInstance(); |
| _hash.add(padding); |
| _hash.add(_message); |
| var innerHash = _hash.close(); |
| |
| // Compute outer padding. |
| for (var i = 0; i < blockSize; i++) { |
| padding[i] = 0x5c ^ _key[i]; |
| } |
| |
| // Outer hash computation which is the result. |
| _hash = _hash.newInstance(); |
| _hash.add(padding); |
| _hash.add(innerHash); |
| return _hash.close(); |
| } |
| |
| /** |
| * Perform the actual computation and extract the message digest |
| * as a list of bytes. |
| */ |
| List<int> close() { |
| _isClosed = true; |
| return digest; |
| } |
| |
| /** |
| * Verify that the HMAC computed for the data so far matches the |
| * given message digest. |
| * |
| * This method should be used instead of memcmp-style comparisons |
| * to avoid leaking information via timing. |
| * |
| * Throws an exception if the given digest does not have the same |
| * size as the digest computed by this HMAC instance. |
| */ |
| bool verify(List<int> digest) { |
| var computedDigest = this.digest; |
| if (digest.length != computedDigest.length) { |
| throw new ArgumentError( |
| 'Invalid digest size: ${digest.length} in HMAC.verify. ' |
| 'Expected: ${_hash.blockSize}.'); |
| } |
| int result = 0; |
| for (var i = 0; i < digest.length; i++) { |
| result |= digest[i] ^ computedDigest[i]; |
| } |
| return result == 0; |
| } |
| |
| // HMAC internal state. |
| Hash _hash; |
| List<int> _key; |
| final List<int> _message; |
| } |