mcs/class/corlib/System.Security.Cryptography/TripleDES.cs

   1 //
   2 // TripleDES.cs: Handles TripleDES (abstract class)
   3 //
   4 // Author:
   5 //      Sebastien Pouliot <sebastien@ximian.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.Globalization;
  32 using System.Security.Cryptography;
  33
  34 namespace System.Security.Cryptography {
  35
  36 // References:
  37 // a.   FIPS PUB 46-3: TripleDES
  38 //      http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf
  39 // b.   ANSI X9.52
  40 //      not free :-(
  41 //      http://webstore.ansi.org/ansidocstore/product.asp?sku=ANSI+X9%2E52%2D1998
  42
  43 public abstract class TripleDES : SymmetricAlgorithm {
  44
  45         public TripleDES ()
  46         {
  47                 // from SymmetricAlgorithm
  48                 KeySizeValue = 192;
  49                 BlockSizeValue = 64;
  50                 FeedbackSizeValue = 8;
  51
  52                 LegalKeySizesValue = new KeySizes [1];
  53                 LegalKeySizesValue [0] = new KeySizes (128, 192, 64);
  54
  55                 LegalBlockSizesValue = new KeySizes [1];
  56                 LegalBlockSizesValue [0] = new KeySizes (64, 64, 0);
  57         }
  58
  59         public override byte[] Key {
  60                 get {
  61                         if (KeyValue == null) {
  62                                 // generate keys as long as we get weak keys
  63                                 GenerateKey ();
  64                                 while (IsWeakKey (KeyValue))
  65                                         GenerateKey ();
  66                         }
  67                         return (byte[]) KeyValue.Clone ();
  68                 }
  69                 set {
  70                         if (value == null)
  71                                 throw new ArgumentNullException ("Key");
  72                         // this will check for both key size and weak keys
  73                         if (IsWeakKey (value))
  74                                 throw new CryptographicException (Locale.GetText ("Weak Key"));
  75                         KeyValue = (byte[]) value.Clone ();
  76                 }
  77         }
  78
  79         // Triple DES is DES in EDE = Encrypt - Decrypt - Encrypt
  80         // with 2 keys (a,b)
  81         //      EDE = Encrypt (a) - Decrypt (b) - Encrypt (a)
  82         //      if a == b then TripleDES == DES(a) (hence weak key)
  83         // with 3 keys (a,b,c)
  84         //      EDE = Encrypt (a) - Decrypt (b) - Encrypt (c)
  85         //      if ( a == b ) then TripleDES == DES(c) (hence weak key)
  86         //      if ( b == c ) then TripleDES == DES(a) (hence weak key)
  87         public static bool IsWeakKey (byte[] rgbKey)
  88         {
  89                 // 128 bits (16 bytes) is 3 DES with 2 keys
  90                 if (rgbKey.Length == 16) {
  91                         // weak if first half == second half
  92                         for (int i = 0; i < 8; i++)
  93                                 if (rgbKey [i] != rgbKey [i+8])
  94                                         return false;
  95                 }
  96                 // 192 bits (24 bytes) is 3 DES with 3 keys
  97                 else if (rgbKey.Length == 24) {
  98                         bool bFirstCase = true;
  99                         // weak if first third == second third
 100                         for (int i = 0; i < 8; i++) {
 101                                 if (rgbKey [i] != rgbKey [i+8]) {
 102                                         bFirstCase = false;
 103                                         break;
 104                                 }
 105                         }
 106                         // weak if second third == third third
 107                         if (!bFirstCase) {
 108                                 for (int i = 8; i < 16; i++)
 109                                         if (rgbKey [i] != rgbKey [i+8])
 110                                                 return false;
 111                         }
 112                 }
 113                 else
 114                         throw new CryptographicException (Locale.GetText ("Wrong Key Length"));
 115
 116                 return true;
 117         }
 118
 119         public static new TripleDES Create ()
 120         {
 121                 return Create ("System.Security.Cryptography.TripleDES");
 122         }
 123
 124         public static new TripleDES Create (string str)
 125         {
 126                 return (TripleDES) CryptoConfig.CreateFromName (str);
 127         }
 128 }
 129
 130 }