TripleDES.cs :  » 2.6.4-mono-.net-core » System.Security » System » Security » Cryptography » C# / CSharp Open Source

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C# / CSharp Open Source » 2.6.4 mono .net core » System.Security 
System.Security » System » Security » Cryptography » TripleDES.cs
//
// TripleDES.cs: Handles TripleDES (abstract class)
//
// Author:
//  Sebastien Pouliot <sebastien@ximian.com>
//
// (C) 2002, 2003 Motus Technologies Inc. (http://www.motus.com)
// Copyright (C) 2004-2006 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.Globalization;
using System.Runtime.InteropServices;
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

[ComVisible (true)]
public abstract class TripleDES : SymmetricAlgorithm {

  protected TripleDES ()
  {
    // from SymmetricAlgorithm
    KeySizeValue = 192;
    BlockSizeValue = 64;
    FeedbackSizeValue = 8;

    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)
  {
    if (rgbKey == null)
      throw new CryptographicException (Locale.GetText ("Null Key"));
    // 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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