Add base 64 encoding to the crypto library utils.

lib/crypto/crypto_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.
 
+class _LineWrappingStringBuffer {
+  _LineWrappingStringBuffer(int this._lineLength) : _sb = new StringBuffer();
+
+  void add(String s) {
+    if (_lineLength !== null && _currentLineLength == _lineLength) {
+      _sb.add('\r\n');
+      _currentLineLength = 0;
+    }
+    _sb.add(s);
+    _currentLineLength++;
+  }
+
+  String toString() => _sb.toString();
+
+  int _lineLength;
+  StringBuffer _sb;
+  int _currentLineLength = 0;
+}
+
 class _CryptoUtils {
   static String bytesToHex(List<int> bytes) {
     var result = new StringBuffer();
     for (var part in bytes) {
       result.add('${part < 16 ? '0' : ''}${part.toRadixString(16)}');
     }
     return result.toString();
   }
+
+  static String bytesToBase64(List<int> bytes, [int lineLength]) {
+    final table =
+        const [ 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
+                'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
+                'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
+                'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
+                'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7',
+                '8', '9', '+', '/' ];
+
+    var result = new _LineWrappingStringBuffer(lineLength);
+
+    // Encode all full 24-bit blocks.
+    var i = 0;
+    for (; (i + 2) < bytes.length; i += 3) {
+      var b0 = bytes[i] & 0xff;
+      var b1 = bytes[i + 1] & 0xff;
+      var b2 = bytes[i + 2] & 0xff;
+      result.add(table[b0 >> 2]);
+      result.add(table[((b0 << 4) | (b1 >> 4)) & 0x3f]);
+      result.add(table[((b1 << 2) | (b2 >> 6)) & 0x3f]);
+      result.add(table[b2 & 0x3f]);
+    }
+
+    // Deal with the last non-full block if any and add padding '='.
+    if (i == bytes.length - 1) {
+      var b0 = bytes[i] & 0xff;
+      result.add(table[b0 >> 2]);
+      result.add(table[(b0 << 4) & 0x3f]);
+      result.add('=');
+      result.add('=');
+    } else if (i == bytes.length - 2) {
+      var b0 = bytes[i] & 0xff;
+      var b1 = bytes[i + 1] & 0xff;
+      result.add(table[b0 >> 2]);
+      result.add(table[((b0 << 4) | (b1 >> 4)) & 0x3f]);
+      result.add(table[(b1 << 2) & 0x3f]);
+      result.add('=');
+    }
+
+    return result.toString();
+  }
 }