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) 2004-2006 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.Globalization;
  31 using System.Runtime.InteropServices;
  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 [ComVisible (true)]
  44 public abstract class TripleDES : SymmetricAlgorithm {
  45
  46         protected TripleDES ()
  47         {
  48                 // from SymmetricAlgorithm
  49                 KeySizeValue = 192;
  50                 BlockSizeValue = 64;
  51                 FeedbackSizeValue = 8;
  52
  53                 LegalKeySizesValue = new KeySizes [1];
  54                 LegalKeySizesValue [0] = new KeySizes (128, 192, 64);
  55
  56                 LegalBlockSizesValue = new KeySizes [1];
  57                 LegalBlockSizesValue [0] = new KeySizes (64, 64, 0);
  58         }
  59
  60         public override byte[] Key {
  61                 get {
  62                         if (KeyValue == null) {
  63                                 // generate keys as long as we get weak keys
  64                                 GenerateKey ();
  65                                 while (IsWeakKey (KeyValue))
  66                                         GenerateKey ();
  67                         }
  68                         return (byte[]) KeyValue.Clone ();
  69                 }
  70                 set {
  71                         if (value == null)
  72                                 throw new ArgumentNullException ("Key");
  73                         // this will check for both key size and weak keys
  74                         if (IsWeakKey (value))
  75                                 throw new CryptographicException (Locale.GetText ("Weak Key"));
  76                         KeyValue = (byte[]) value.Clone ();
  77                 }
  78         }
  79
  80         // Triple DES is DES in EDE = Encrypt - Decrypt - Encrypt
  81         // with 2 keys (a,b)
  82         //      EDE = Encrypt (a) - Decrypt (b) - Encrypt (a)
  83         //      if a == b then TripleDES == DES(a) (hence weak key)
  84         // with 3 keys (a,b,c)
  85         //      EDE = Encrypt (a) - Decrypt (b) - Encrypt (c)
  86         //      if ( a == b ) then TripleDES == DES(c) (hence weak key)
  87         //      if ( b == c ) then TripleDES == DES(a) (hence weak key)
  88         public static bool IsWeakKey (byte[] rgbKey)
  89         {
  90                 if (rgbKey == null)
  91                         throw new CryptographicException (Locale.GetText ("Null Key"));
  92                 // 128 bits (16 bytes) is 3 DES with 2 keys
  93                 if (rgbKey.Length == 16) {
  94                         // weak if first half == second half
  95                         for (int i = 0; i < 8; i++)
  96                                 if (rgbKey [i] != rgbKey [i+8])
  97                                         return false;
  98                 }
  99                 // 192 bits (24 bytes) is 3 DES with 3 keys
 100                 else if (rgbKey.Length == 24) {
 101                         bool bFirstCase = true;
 102                         // weak if first third == second third
 103                         for (int i = 0; i < 8; i++) {
 104                                 if (rgbKey [i] != rgbKey [i+8]) {
 105                                         bFirstCase = false;
 106                                         break;
 107                                 }
 108                         }
 109                         // weak if second third == third third
 110                         if (!bFirstCase) {
 111                                 for (int i = 8; i < 16; i++)
 112                                         if (rgbKey [i] != rgbKey [i+8])
 113                                                 return false;
 114                         }
 115                 }
 116                 else
 117                         throw new CryptographicException (Locale.GetText ("Wrong Key Length"));
 118
 119                 return true;
 120         }
 121
 122         public static new TripleDES Create ()
 123         {
 124                 return Create ("System.Security.Cryptography.TripleDES");
 125         }
 126
 127         public static new TripleDES Create (string str)
 128         {
 129                 return (TripleDES) CryptoConfig.CreateFromName (str);
 130         }
 131 }
 132
 133 }
 134