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)
10 // Permission is hereby granted, free of charge, to any person obtaining
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15 // permit persons to whom the Software is furnished to do so, subject to
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32 using System
.Globalization
;
33 using System
.Runtime
.InteropServices
;
34 using System
.Security
.Cryptography
;
36 namespace System
.Security
.Cryptography
{
39 // a. FIPS PUB 46-3: TripleDES
40 // http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf
43 // http://webstore.ansi.org/ansidocstore/product.asp?sku=ANSI+X9%2E52%2D1998
46 public abstract class TripleDES
: SymmetricAlgorithm
{
48 protected TripleDES ()
50 // from SymmetricAlgorithm
53 FeedbackSizeValue
= 8;
55 LegalKeySizesValue
= new KeySizes
[1];
56 LegalKeySizesValue
[0] = new KeySizes (128, 192, 64);
58 LegalBlockSizesValue
= new KeySizes
[1];
59 LegalBlockSizesValue
[0] = new KeySizes (64, 64, 0);
62 public override byte[] Key
{
64 if (KeyValue
== null) {
65 // generate keys as long as we get weak keys
67 while (IsWeakKey (KeyValue
))
70 return (byte[]) KeyValue
.Clone ();
74 throw new ArgumentNullException ("Key");
75 // this will check for both key size and weak keys
76 if (IsWeakKey (value))
77 throw new CryptographicException (Locale
.GetText ("Weak Key"));
78 KeyValue
= (byte[]) value.Clone ();
82 // Triple DES is DES in EDE = Encrypt - Decrypt - Encrypt
84 // EDE = Encrypt (a) - Decrypt (b) - Encrypt (a)
85 // if a == b then TripleDES == DES(a) (hence weak key)
86 // with 3 keys (a,b,c)
87 // EDE = Encrypt (a) - Decrypt (b) - Encrypt (c)
88 // if ( a == b ) then TripleDES == DES(c) (hence weak key)
89 // if ( b == c ) then TripleDES == DES(a) (hence weak key)
90 public static bool IsWeakKey (byte[] rgbKey
)
93 throw new CryptographicException (Locale
.GetText ("Null Key"));
94 // 128 bits (16 bytes) is 3 DES with 2 keys
95 if (rgbKey
.Length
== 16) {
96 // weak if first half == second half
97 for (int i
= 0; i
< 8; i
++)
98 if (rgbKey
[i
] != rgbKey
[i
+8])
101 // 192 bits (24 bytes) is 3 DES with 3 keys
102 else if (rgbKey
.Length
== 24) {
103 bool bFirstCase
= true;
104 // weak if first third == second third
105 for (int i
= 0; i
< 8; i
++) {
106 if (rgbKey
[i
] != rgbKey
[i
+8]) {
111 // weak if second third == third third
113 for (int i
= 8; i
< 16; i
++)
114 if (rgbKey
[i
] != rgbKey
[i
+8])
119 throw new CryptographicException (Locale
.GetText ("Wrong Key Length"));
124 public static new TripleDES
Create ()
126 return Create ("System.Security.Cryptography.TripleDES");
129 public static new TripleDES
Create (string str
)
131 return (TripleDES
) CryptoConfig
.CreateFromName (str
);