Add common interface for cryptographic hash functions to lib/crypto.dart.

lib/crypto/sha_utils.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.
+
+// Constants.
+final _MASK_8 = 0xff;
+final _MASK_32 = 0xffffffff;
+final _BITS_PER_BYTE = 8;
+final _BYTES_PER_WORD = 4;
+
+// Base class encapsulating common behavior for SHA cryptographic hash
+// functions.
+class _SHACryptoHashBase implements CryptoHash {
+  _SHACryptoHashBase(int this._chunkSizeInWords, int this._digestSizeInWords)
+      : _pendingData = [] {
+    _currentChunk = new List(_chunkSizeInWords);
+    _h = new List(_digestSizeInWords);
+  }
+
+  // Update the hasher with more data.
+  _SHACryptoHashBase update(List<int> data) {
+    if (_digestCalled) {
+      throw new CryptoHashException(
+          'CryptoHash update method called after digest');
+    }
+    _lengthInBytes += data.length;
+    _pendingData.addAll(data);
+    _iterate();
+    return this;
+  }
+
+  // Finish the hash computation and return the digest string.
+  List<int> digest() {
+    if (_digestCalled) {
+      throw new CryptoHashException(
+          'CryptoHash digest method called more than once');
+    }
+    _digestCalled = true;
+    _finalizeData();
+    _iterate();
+    assert(_pendingData.length == 0);
+    var result = [];
+    for (var i = 0; i < _h.length; i++) {
+      result.addAll(_wordToBytes(_h[i]));
+    }
+    return result;
+  }
+
+  // One round of the hash computation.
+  abstract _updateHash(List<int> m);
+
+  // Helper methods.
+  _add32(x, y) => (x + y) & _MASK_32;
+  _roundUp(val, n) => (val + n - 1) & -n;
+
+  // Converts a list of bytes to a chunk of 32-bit words.
+  _bytesToChunk(List<int> data, int dataIndex) {
+    assert((data.length - dataIndex) >= (_chunkSizeInWords * _BYTES_PER_WORD));
+    for (var wordIndex = 0; wordIndex < _chunkSizeInWords; wordIndex++) {
+      var word = (data[dataIndex++] & 0xff) << 24;
+      word |= (data[dataIndex++] & _MASK_8) << 16;
+      word |= (data[dataIndex++] & _MASK_8) << 8;
+      word |= (data[dataIndex++] & _MASK_8);
+      _currentChunk[wordIndex] = word;
+    }
+  }
+
+  // Convert a 32-bit word to four bytes.
+  _wordToBytes(int word) {
+    List<int> bytes = new List(_BYTES_PER_WORD);
+    bytes[0] = word >> 24;
+    bytes[1] = (word >> 16) & _MASK_8;
+    bytes[2] = (word >> 8) & _MASK_8;
+    bytes[3] = word & _MASK_8;
+    return bytes;
+  }
+
+  // Iterate through data updating the hash computation for each
+  // chunk.
+  _iterate() {
+    var len = _pendingData.length;
+    var chunkSizeInBytes = _chunkSizeInWords * _BYTES_PER_WORD;
+    if (len >= chunkSizeInBytes) {
+      var index = 0;
+      for (; (len - index) >= chunkSizeInBytes; index += chunkSizeInBytes) {
+        _bytesToChunk(_pendingData, index);
+        _updateHash(_currentChunk);
+      }
+      var remaining = len - index;
+      _pendingData = _pendingData.getRange(index, remaining);
+    }
+  }
+
+  // Finalize the data. Add a 1 bit to the end of the message. Expand with
+  // 0 bits and the length of the message.
+  _finalizeData() {
+    _pendingData.add(0x80);
+    var contentsLength = _lengthInBytes + 9;
+    var chunkSizeInBytes = _chunkSizeInWords * _BYTES_PER_WORD;
+    var finalizedLength = _roundUp(contentsLength, chunkSizeInBytes);
+    var zeroPadding = finalizedLength - contentsLength;
+    for (var i = 0; i < zeroPadding; i++) {
+      _pendingData.add(0);
+    }
+    var lengthInBits = _lengthInBytes * _BITS_PER_BYTE;
+    _pendingData.addAll(_wordToBytes(lengthInBits >> 32));
+    _pendingData.addAll(_wordToBytes(lengthInBits & _MASK_32));
+  }
+
+  // Hasher state.
+  int _lengthInBytes = 0;
+  int _chunkSizeInWords;
+  int _digestSizeInWords;
+  List<int> _pendingData;
+  List<int> _currentChunk;
+  List<int> _h;
+  bool _digestCalled = false;
+}