139 lines
4.1 KiB
C#
139 lines
4.1 KiB
C#
//
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// TripleDES.cs: Handles TripleDES (abstract class)
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//
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// Author:
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// Sebastien Pouliot <sebastien@ximian.com>
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//
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// (C) 2002, 2003 Motus Technologies Inc. (http://www.motus.com)
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// Copyright (C) 2004-2006 Novell, Inc (http://www.novell.com)
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//
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// Permission is hereby granted, free of charge, to any person obtaining
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// a copy of this software and associated documentation files (the
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// "Software"), to deal in the Software without restriction, including
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// without limitation the rights to use, copy, modify, merge, publish,
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// distribute, sublicense, and/or sell copies of the Software, and to
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// permit persons to whom the Software is furnished to do so, subject to
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// the following conditions:
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//
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// The above copyright notice and this permission notice shall be
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// included in all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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//
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using System.Globalization;
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using System.Runtime.InteropServices;
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using System.Security.Cryptography;
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namespace System.Security.Cryptography {
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// References:
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// a. FIPS PUB 46-3: TripleDES
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// http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf
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// b. ANSI X9.52
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// not free :-(
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// http://webstore.ansi.org/ansidocstore/product.asp?sku=ANSI+X9%2E52%2D1998
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[ComVisible (true)]
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public abstract class TripleDES : SymmetricAlgorithm {
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protected TripleDES ()
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{
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// from SymmetricAlgorithm
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KeySizeValue = 192;
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BlockSizeValue = 64;
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FeedbackSizeValue = 8;
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LegalKeySizesValue = new KeySizes [1];
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LegalKeySizesValue [0] = new KeySizes (128, 192, 64);
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LegalBlockSizesValue = new KeySizes [1];
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LegalBlockSizesValue [0] = new KeySizes (64, 64, 0);
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}
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public override byte[] Key {
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get {
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if (KeyValue == null) {
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// generate keys as long as we get weak keys
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GenerateKey ();
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while (IsWeakKey (KeyValue))
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GenerateKey ();
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}
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return (byte[]) KeyValue.Clone ();
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}
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set {
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if (value == null)
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throw new ArgumentNullException ("Key");
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// this will check for both key size and weak keys
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if (IsWeakKey (value))
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throw new CryptographicException (Locale.GetText ("Weak Key"));
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KeyValue = (byte[]) value.Clone ();
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}
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}
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// Triple DES is DES in EDE = Encrypt - Decrypt - Encrypt
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// with 2 keys (a,b)
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// EDE = Encrypt (a) - Decrypt (b) - Encrypt (a)
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// if a == b then TripleDES == DES(a) (hence weak key)
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// with 3 keys (a,b,c)
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// EDE = Encrypt (a) - Decrypt (b) - Encrypt (c)
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// if ( a == b ) then TripleDES == DES(c) (hence weak key)
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// if ( b == c ) then TripleDES == DES(a) (hence weak key)
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public static bool IsWeakKey (byte[] rgbKey)
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{
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if (rgbKey == null)
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throw new CryptographicException (Locale.GetText ("Null Key"));
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// 128 bits (16 bytes) is 3 DES with 2 keys
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if (rgbKey.Length == 16) {
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// weak if first half == second half
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for (int i = 0; i < 8; i++)
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if (rgbKey [i] != rgbKey [i+8])
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return false;
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}
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// 192 bits (24 bytes) is 3 DES with 3 keys
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else if (rgbKey.Length == 24) {
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bool bFirstCase = true;
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// weak if first third == second third
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for (int i = 0; i < 8; i++) {
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if (rgbKey [i] != rgbKey [i+8]) {
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bFirstCase = false;
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break;
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}
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}
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// weak if second third == third third
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if (!bFirstCase) {
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for (int i = 8; i < 16; i++)
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if (rgbKey [i] != rgbKey [i+8])
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return false;
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}
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}
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else
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throw new CryptographicException (Locale.GetText ("Wrong Key Length"));
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return true;
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}
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public static new TripleDES Create ()
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{
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#if FULL_AOT_RUNTIME
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return new System.Security.Cryptography.TripleDESCryptoServiceProvider ();
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#else
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return Create ("System.Security.Cryptography.TripleDES");
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#endif
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}
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public static new TripleDES Create (string str)
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{
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return (TripleDES) CryptoConfig.CreateFromName (str);
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}
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}
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}
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