mcs/class/corlib/Mono.Security.Cryptography/MACAlgorithm.cs

   1 //
   2 // MACAlgorithm.cs: Handles MAC with any symmetric algorithm
   3 //
   4 // Author:
   5 //      Sebastien Pouliot (spouliot@motus.com)
   6 //
   7 // (C) 2002, 2003 Motus Technologies Inc. (http://www.motus.com)
   8 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
   9 //
  10 // Permission is hereby granted, free of charge, to any person obtaining
  11 // a copy of this software and associated documentation files (the
  12 // "Software"), to deal in the Software without restriction, including
  13 // without limitation the rights to use, copy, modify, merge, publish,
  14 // distribute, sublicense, and/or sell copies of the Software, and to
  15 // permit persons to whom the Software is furnished to do so, subject to
  16 // the following conditions:
  17 //
  18 // The above copyright notice and this permission notice shall be
  19 // included in all copies or substantial portions of the Software.
  20 //
  21 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  22 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  23 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  24 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  25 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  26 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  27 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  28 //
  29
  30 using System;
  31 using System.Security.Cryptography;
  32
  33 namespace Mono.Security.Cryptography {
  34
  35         // References:
  36         // a.   FIPS PUB 81: DES MODES OF OPERATION
  37         //      MAC: Appendix F (MACDES not MACTripleDES but close enough ;-)
  38         //      http://www.itl.nist.gov/fipspubs/fip81.htm
  39
  40         // Generic MAC mechanims - most of the work is done in here
  41         // It should work with any symmetric algorithm function e.g. DES for MACDES (fips81)
  42         internal class MACAlgorithm {
  43
  44                 private SymmetricAlgorithm algo;
  45                 private ICryptoTransform enc;
  46                 private byte[] block;
  47                 private int blockSize;
  48                 private int blockCount;
  49
  50                 public MACAlgorithm (SymmetricAlgorithm algorithm)
  51                 {
  52                         algo = (SymmetricAlgorithm) algorithm;
  53                         algo.Mode = CipherMode.CBC;
  54                         blockSize = (algo.BlockSize >> 3); // in bytes
  55                         algo.IV = new byte [blockSize];
  56                         block = new byte [blockSize];
  57                 }
  58
  59                 public void Initialize (byte[] key)
  60                 {
  61                         algo.Key = key;
  62                         // note: the encryptor transform may be reusable - see Final
  63                         if (enc == null) {
  64                                 enc = algo.CreateEncryptor ();
  65                         }
  66                         Array.Clear (block, 0, blockSize);
  67                         blockCount = 0;
  68                 }
  69
  70                 public void Core (byte[] rgb, int ib, int cb)
  71                 {
  72                         // 1. fill the rest of the "block"
  73                         int n = System.Math.Min (blockSize - blockCount, cb);
  74                         Array.Copy (rgb, ib, block, blockCount, n);
  75                         blockCount += n;
  76
  77                         // 2. if block is full then transform it
  78                         if (blockCount == blockSize) {
  79                                 enc.TransformBlock (block, 0, blockSize, block, 0);
  80
  81                                 // 3. transform any other full block in specified buffer
  82                                 int b = (int) ((cb - n) / blockSize);
  83                                 for (int i=0; i < b; i++) {
  84                                         enc.TransformBlock (rgb, n, blockSize, block, 0);
  85                                         n += blockSize;
  86                                 }
  87
  88                                 // 4. if data is still present fill the "block" with the remainder
  89                                 blockCount = cb - n;
  90                                 if (blockCount > 0)
  91                                         Array.Copy (rgb, n, block, 0, blockCount);
  92                         }
  93                 }
  94
  95                 public byte[] Final ()
  96                 {
  97                         byte[] result;
  98                         if (blockCount > 0)
  99                                 result = enc.TransformFinalBlock (block, 0, blockCount);
 100                         else {
 101 #if NET_1_0
 102                                 // add an empty (zeros) block for MAC padding
 103                                 byte[] emptyBlock = new byte [blockSize];
 104                                 result = enc.TransformFinalBlock (emptyBlock, 0, blockSize);
 105 #else
 106                                 result = (byte[]) block.Clone ();
 107 #endif
 108                         }
 109                         if (!enc.CanReuseTransform) {
 110                                 enc.Dispose ();
 111                                 enc = null;
 112                         }
 113                         return result;
 114                 }
 115         }
 116 }