Remove the crypto factories

pkg/crypto/lib/src/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.
 
 part of crypto;
 
-class _HMAC implements HMAC {
+/**
+ * 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;
 
-  _HMAC(Hash this._hash, List<int> this._key) : _message = [];
+  /**
+   * 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.
+   */
   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();
     }
 
@@ skipping 24 matching lines @@
       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;
   List<int> _message;
 }