2 // TripleDES.cs: Handles TripleDES (abstract class)
5 // Sebastien Pouliot <sebastien@ximian.com>
7 // (C) 2002, 2003 Motus Technologies Inc. (http://www.motus.com)
8 // Copyright (C) 2004-2006 Novell, Inc (http://www.novell.com)
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30 using System.Globalization;
31 using System.Runtime.InteropServices;
32 using System.Security.Cryptography;
34 namespace System.Security.Cryptography {
37 // a. FIPS PUB 46-3: TripleDES
38 // http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf
41 // http://webstore.ansi.org/ansidocstore/product.asp?sku=ANSI+X9%2E52%2D1998
44 public abstract class TripleDES : SymmetricAlgorithm {
46 protected TripleDES ()
48 // from SymmetricAlgorithm
51 FeedbackSizeValue = 8;
53 LegalKeySizesValue = new KeySizes [1];
54 LegalKeySizesValue [0] = new KeySizes (128, 192, 64);
56 LegalBlockSizesValue = new KeySizes [1];
57 LegalBlockSizesValue [0] = new KeySizes (64, 64, 0);
60 public override byte[] Key {
62 if (KeyValue == null) {
63 // generate keys as long as we get weak keys
65 while (IsWeakKey (KeyValue))
68 return (byte[]) KeyValue.Clone ();
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 ();
80 // Triple DES is DES in EDE = Encrypt - Decrypt - Encrypt
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)
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])
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]) {
109 // weak if second third == third third
111 for (int i = 8; i < 16; i++)
112 if (rgbKey [i] != rgbKey [i+8])
117 throw new CryptographicException (Locale.GetText ("Wrong Key Length"));
122 public static new TripleDES Create ()
124 return Create ("System.Security.Cryptography.TripleDES");
127 public static new TripleDES Create (string str)
129 return (TripleDES) CryptoConfig.CreateFromName (str);