mcs/class/referencesource/mscorlib/system/security/cryptography/tripledes.cs

   1 using System.Diagnostics.Contracts;
   2 // ==++==
   3 //
   4 //   Copyright (c) Microsoft Corporation.  All rights reserved.
   5 //
   6 // ==--==
   7 // <OWNER>[....]</OWNER>
   8 //
   9
  10 //
  11 // TripleDES.cs
  12 //
  13
  14 namespace System.Security.Cryptography {
  15 [System.Runtime.InteropServices.ComVisible(true)]
  16     public abstract class TripleDES : SymmetricAlgorithm
  17     {
  18         private static  KeySizes[] s_legalBlockSizes = {
  19             new KeySizes(64, 64, 0)
  20         };
  21
  22         private static  KeySizes[] s_legalKeySizes = {
  23             new KeySizes(2*64, 3*64, 64)
  24         };
  25
  26         //
  27         // protected constructors
  28         //
  29
  30         protected TripleDES() {
  31             KeySizeValue = 3*64;
  32             BlockSizeValue = 64;
  33             FeedbackSizeValue = BlockSizeValue;
  34             LegalBlockSizesValue = s_legalBlockSizes;
  35             LegalKeySizesValue = s_legalKeySizes;
  36         }
  37
  38         //
  39         // public properties
  40         //
  41
  42         public override byte[] Key {
  43             get {
  44                 if (KeyValue == null) {
  45                     // Never hand back a weak key
  46                     do {
  47                         GenerateKey();
  48                     } while (IsWeakKey(KeyValue));
  49                 }
  50                 return (byte[]) KeyValue.Clone();
  51             }
  52             set {
  53                 if (value == null) throw new ArgumentNullException("value");
  54                 Contract.EndContractBlock();
  55                 if (!ValidKeySize(value.Length * 8)) { // must convert bytes to bits
  56                     throw new CryptographicException(Environment.GetResourceString("Cryptography_InvalidKeySize"));
  57                 }
  58                 if (IsWeakKey(value)) {
  59                     throw new CryptographicException(Environment.GetResourceString("Cryptography_InvalidKey_Weak"),"TripleDES");
  60                 }
  61                 KeyValue = (byte[]) value.Clone();
  62                 KeySizeValue = value.Length * 8;
  63             }
  64         }
  65
  66         //
  67         // public methods
  68         //
  69
  70         new static public TripleDES Create() {
  71             return Create("System.Security.Cryptography.TripleDES");
  72         }
  73
  74         new static public TripleDES Create(String str) {
  75             return (TripleDES) CryptoConfig.CreateFromName(str);
  76         }
  77
  78         public static bool IsWeakKey(byte[] rgbKey) {
  79             // All we have to check for here is (a) we're in 3-key mode (192 bits), and
  80             // (b) either K1 == K2 or K2 == K3
  81             if (!IsLegalKeySize(rgbKey)) {
  82                 throw new CryptographicException(Environment.GetResourceString("Cryptography_InvalidKeySize"));
  83             }
  84             byte[] rgbOddParityKey = Utils.FixupKeyParity(rgbKey);
  85             if (EqualBytes(rgbOddParityKey,0,8,8)) return(true);
  86             if ((rgbOddParityKey.Length == 24) && EqualBytes(rgbOddParityKey,8,16,8)) return(true);
  87             return(false);
  88         }
  89
  90         //
  91         // private methods
  92         //
  93
  94         private static bool EqualBytes(byte[] rgbKey, int start1, int start2, int count) {
  95             if (start1 < 0) throw new ArgumentOutOfRangeException("start1", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
  96             if (start2 < 0) throw new ArgumentOutOfRangeException("start2", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
  97             if ((start1+count) > rgbKey.Length) throw new ArgumentException(Environment.GetResourceString("Argument_InvalidValue"));
  98             if ((start2+count) > rgbKey.Length) throw new ArgumentException(Environment.GetResourceString("Argument_InvalidValue"));
  99             Contract.EndContractBlock();
 100             for (int i = 0; i < count; i++) {
 101                 if (rgbKey[start1+i] != rgbKey[start2+i]) return(false);
 102             }
 103             return(true);
 104         }
 105
 106         private static bool IsLegalKeySize(byte[] rgbKey) {
 107             if (rgbKey != null && ((rgbKey.Length == 16) || (rgbKey.Length == 24)))
 108                 return(true);
 109             return(false);
 110         }
 111     }
 112 }