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 #if !NET_2_1 || MONOTOUCH
  31
  32 using System.Globalization;
  33 using System.Runtime.InteropServices;
  34 using System.Security.Cryptography;
  35
  36 namespace System.Security.Cryptography {
  37
  38 // References:
  39 // a.   FIPS PUB 46-3: TripleDES
  40 //      http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf
  41 // b.   ANSI X9.52
  42 //      not free :-(
  43 //      http://webstore.ansi.org/ansidocstore/product.asp?sku=ANSI+X9%2E52%2D1998
  44
  45 #if NET_2_0
  46 [ComVisible (true)]
  47 #endif
  48 public abstract class TripleDES : SymmetricAlgorithm {
  49
  50 #if NET_2_0
  51         protected TripleDES ()
  52 #else
  53         public TripleDES ()
  54 #endif
  55         {
  56                 // from SymmetricAlgorithm
  57                 KeySizeValue = 192;
  58                 BlockSizeValue = 64;
  59                 FeedbackSizeValue = 8;
  60
  61                 LegalKeySizesValue = new KeySizes [1];
  62                 LegalKeySizesValue [0] = new KeySizes (128, 192, 64);
  63
  64                 LegalBlockSizesValue = new KeySizes [1];
  65                 LegalBlockSizesValue [0] = new KeySizes (64, 64, 0);
  66         }
  67
  68         public override byte[] Key {
  69                 get {
  70                         if (KeyValue == null) {
  71                                 // generate keys as long as we get weak keys
  72                                 GenerateKey ();
  73                                 while (IsWeakKey (KeyValue))
  74                                         GenerateKey ();
  75                         }
  76                         return (byte[]) KeyValue.Clone ();
  77                 }
  78                 set {
  79                         if (value == null)
  80                                 throw new ArgumentNullException ("Key");
  81                         // this will check for both key size and weak keys
  82                         if (IsWeakKey (value))
  83                                 throw new CryptographicException (Locale.GetText ("Weak Key"));
  84                         KeyValue = (byte[]) value.Clone ();
  85                 }
  86         }
  87
  88         // Triple DES is DES in EDE = Encrypt - Decrypt - Encrypt
  89         // with 2 keys (a,b)
  90         //      EDE = Encrypt (a) - Decrypt (b) - Encrypt (a)
  91         //      if a == b then TripleDES == DES(a) (hence weak key)
  92         // with 3 keys (a,b,c)
  93         //      EDE = Encrypt (a) - Decrypt (b) - Encrypt (c)
  94         //      if ( a == b ) then TripleDES == DES(c) (hence weak key)
  95         //      if ( b == c ) then TripleDES == DES(a) (hence weak key)
  96         public static bool IsWeakKey (byte[] rgbKey)
  97         {
  98 #if NET_2_0
  99                 if (rgbKey == null)
 100                         throw new CryptographicException (Locale.GetText ("Null Key"));
 101 #endif
 102                 // 128 bits (16 bytes) is 3 DES with 2 keys
 103                 if (rgbKey.Length == 16) {
 104                         // weak if first half == second half
 105                         for (int i = 0; i < 8; i++)
 106                                 if (rgbKey [i] != rgbKey [i+8])
 107                                         return false;
 108                 }
 109                 // 192 bits (24 bytes) is 3 DES with 3 keys
 110                 else if (rgbKey.Length == 24) {
 111                         bool bFirstCase = true;
 112                         // weak if first third == second third
 113                         for (int i = 0; i < 8; i++) {
 114                                 if (rgbKey [i] != rgbKey [i+8]) {
 115                                         bFirstCase = false;
 116                                         break;
 117                                 }
 118                         }
 119                         // weak if second third == third third
 120                         if (!bFirstCase) {
 121                                 for (int i = 8; i < 16; i++)
 122                                         if (rgbKey [i] != rgbKey [i+8])
 123                                                 return false;
 124                         }
 125                 }
 126                 else
 127                         throw new CryptographicException (Locale.GetText ("Wrong Key Length"));
 128
 129                 return true;
 130         }
 131
 132         public static new TripleDES Create ()
 133         {
 134                 return Create ("System.Security.Cryptography.TripleDES");
 135         }
 136
 137         public static new TripleDES Create (string str)
 138         {
 139                 return (TripleDES) CryptoConfig.CreateFromName (str);
 140         }
 141 }
 142
 143 }
 144
 145 #endif
 146