package gnu.crypto.cipher;
// ----------------------------------------------------------------------------
// $Id: TripleDES.java,v 1.2 2005/10/06 04:24:14 rsdio Exp $
//
// Copyright (C) 2002, Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2, or (at your option)
// any later version.
//
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; see the file COPYING. If not, write to the
//
// Free Software Foundation Inc.,
// 51 Franklin Street, Fifth Floor,
// Boston, MA 02110-1301
// USA
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library. Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
//
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// you permission to link this library with independent modules to
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// do so, delete this exception statement from your version.
//
// --------------------------------------------------------------------------
import gnu.crypto.Registry;
import java.util.Collections;
import java.util.Iterator;
import java.security.InvalidKeyException;
/**
* Triple-DES, 3DES, or DESede is a <i>combined cipher</i> that uses
* three iterations of the Data Encryption Standard cipher to improve
* the security (at the cost of speed) of plain DES.
*
* <p>Triple-DES runs the DES algorithm three times with three
* independent 56 bit keys. To encrypt:</p>
*
* <blockquote><i>C<sub>i</sub> =
* E<sub>k3</sub> ( E<sub>k2</sub><sup>-1</sup> ( E<sub>k1</sub> ( P<sub>i</sub> )))</i></blockquote>
*
* <p>And to decrypt:</p>
*
* <blockquote><i>P<sub>i</sub> =
* E<sub>k1</sub><sup>-1</sup> ( E<sub>k2</sub> ( E<sub>k3</sub><sup>-1</sup> ( C<sub>i</sub> )))</i></blockquote>
*
* <p>(The "ede" comes from the encryption operation, which runs
* Encrypt-Decrypt-Encrypt)</p>
*
* <p>References:</p>
* <ol>
* <li>Bruce Schneier, <i>Applied Cryptography: Protocols, Algorithms,
* and Source Code in C, Second Edition</i>. (1996 John Wiley and Sons)
* ISBN 0-471-11709-9. Page 294--295.</li>
* </ol>
*
* @version $Revision: 1.2 $
*/
public class TripleDES extends BaseCipher {
// Constants and variables.
// -----------------------------------------------------------------------
/** Triple-DES only operates on 64 bit blocks. */
public static final int BLOCK_SIZE = 8;
/** Triple-DES uses 168 bits of a parity-adjusted 192 bit key. */
public static final int KEY_SIZE = 24;
/** The underlying DES instance. */
private DES des;
// Constructors.
// -----------------------------------------------------------------------
/**
* Default 0-arguments constructor.
*/
public TripleDES() {
super(Registry.TRIPLEDES_CIPHER, BLOCK_SIZE, KEY_SIZE);
des = new DES();
}
// Class methods.
// -----------------------------------------------------------------------
/**
* Transform a key so it will be parity adjusted.
*
* @param kb The key bytes to adjust.
* @param offset The starting offset into the key bytes.
* @see DES#adjustParity(byte[],int)
*/
public static void adjustParity(byte[] kb, int offset) {
DES.adjustParity(kb, offset);
DES.adjustParity(kb, offset + 8);
DES.adjustParity(kb, offset + 16);
}
/**
* Tests if a byte array has already been parity adjusted.
*
* @param kb The key bytes to test.
* @param offset The starting offset into the key bytes.
* @return <code>true</code> if the bytes in <i>kb</i> starting at
* <i>offset</i> are parity adjusted.
* @see DES#isParityAdjusted(byte[],int)
* @see #adjustParity(byte[],int)
*/
public static boolean isParityAdjusted(byte[] kb, int offset) {
return DES.isParityAdjusted(kb, offset)
&& DES.isParityAdjusted(kb, offset + 8)
&& DES.isParityAdjusted(kb, offset + 16);
}
// Methods implementing BaseCipher.
// -----------------------------------------------------------------------
public Object clone() {
return new TripleDES();
}
public Iterator blockSizes() {
return Collections.singleton(new Integer(BLOCK_SIZE)).iterator();
}
public Iterator keySizes() {
return Collections.singleton(new Integer(KEY_SIZE)).iterator();
}
public Object makeKey(byte[] kb, int bs) throws InvalidKeyException {
if (kb.length != KEY_SIZE)
throw new InvalidKeyException("TripleDES key must be 24 bytes");
if (!isParityAdjusted(kb, 0))
adjustParity(kb, 0);
byte[] k1 = new byte[DES.KEY_SIZE], k2 = new byte[DES.KEY_SIZE],
k3 = new byte[DES.KEY_SIZE];
System.arraycopy(kb, 0, k1, 0, DES.KEY_SIZE);
System.arraycopy(kb, DES.KEY_SIZE, k2, 0, DES.KEY_SIZE);
System.arraycopy(kb, 2*DES.KEY_SIZE, k3, 0, DES.KEY_SIZE);
Context ctx = new Context();
ctx.k1 = (DES.Context) des.makeKey(k1, bs);
ctx.k2 = (DES.Context) des.makeKey(k2, bs);
ctx.k3 = (DES.Context) des.makeKey(k3, bs);
return ctx;
}
public void
encrypt(byte[] in, int i, byte[] out, int o, Object K, int bs)
{
byte[] temp = new byte[BLOCK_SIZE];
des.encrypt( in, i, temp, 0, ((Context) K).k1, bs);
des.decrypt(temp, 0, temp, 0, ((Context) K).k2, bs);
des.encrypt(temp, 0, out, o, ((Context) K).k3, bs);
}
public void
decrypt(byte[] in, int i, byte[] out, int o, Object K, int bs)
{
byte[] temp = new byte[BLOCK_SIZE];
des.decrypt( in, i, temp, 0, ((Context) K).k3, bs);
des.encrypt(temp, 0, temp, 0, ((Context) K).k2, bs);
des.decrypt(temp, 0, out, o, ((Context) K).k1, bs);
}
// Inner classes.
// -----------------------------------------------------------------------
private final class Context {
DES.Context k1, k2, k3;
}
}