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//
// TripleDES.cs: Handles TripleDES (abstract class)
//
// Author:
// Sebastien Pouliot <sebastien@ximian.com>
//
// (C) 2002, 2003 Motus Technologies Inc. (http://www.motus.com)
// (C) 2004 Novell (http://www.novell.com)
//
//
// Copyright (C) 2004 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
using System;
using System.Globalization;
using System.Security.Cryptography;
namespace System.Security.Cryptography {
// References:
// a. FIPS PUB 46-3: TripleDES
// http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf
// b. ANSI X9.52
// not free :-(
// http://webstore.ansi.org/ansidocstore/product.asp?sku=ANSI+X9%2E52%2D1998
public abstract class TripleDES : SymmetricAlgorithm {
public TripleDES ()
{
// from SymmetricAlgorithm
KeySizeValue = 192;
BlockSizeValue = 64;
FeedbackSizeValue = 64;
LegalKeySizesValue = new KeySizes [1];
LegalKeySizesValue [0] = new KeySizes (128, 192, 64);
LegalBlockSizesValue = new KeySizes [1];
LegalBlockSizesValue [0] = new KeySizes (64, 64, 0);
}
public override byte[] Key {
get {
if (KeyValue == null) {
// generate keys as long as we get weak keys
GenerateKey ();
while (IsWeakKey (KeyValue))
GenerateKey ();
}
return (byte[]) KeyValue.Clone ();
}
set {
if (value == null)
throw new ArgumentNullException ("Key");
// this will check for both key size and weak keys
if (IsWeakKey (value))
throw new CryptographicException (Locale.GetText ("Weak Key"));
KeyValue = (byte[]) value.Clone ();
}
}
// Triple DES is DES in EDE = Encrypt - Decrypt - Encrypt
// with 2 keys (a,b)
// EDE = Encrypt (a) - Decrypt (b) - Encrypt (a)
// if a == b then TripleDES == DES(a) (hence weak key)
// with 3 keys (a,b,c)
// EDE = Encrypt (a) - Decrypt (b) - Encrypt (c)
// if ( a == b ) then TripleDES == DES(c) (hence weak key)
// if ( b == c ) then TripleDES == DES(a) (hence weak key)
public static bool IsWeakKey (byte[] rgbKey)
{
// 128 bits (16 bytes) is 3 DES with 2 keys
if (rgbKey.Length == 16) {
// weak if first half == second half
for (int i = 0; i < 8; i++)
if (rgbKey [i] != rgbKey [i+8])
return false;
}
// 192 bits (24 bytes) is 3 DES with 3 keys
else if (rgbKey.Length == 24) {
bool bFirstCase = true;
// weak if first third == second third
for (int i = 0; i < 8; i++) {
if (rgbKey [i] != rgbKey [i+8]) {
bFirstCase = false;
break;
}
}
// weak if second third == third third
if (!bFirstCase) {
for (int i = 8; i < 16; i++)
if (rgbKey [i] != rgbKey [i+8])
return false;
}
}
else
throw new CryptographicException (Locale.GetText ("Wrong Key Length"));
return true;
}
public static new TripleDES Create ()
{
return Create ("System.Security.Cryptography.TripleDES");
}
public static new TripleDES Create (string str)
{
return (TripleDES) CryptoConfig.CreateFromName (str);
}
}
}
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