package gnu.crypto.prng;
// ----------------------------------------------------------------------------
// $Id: ARCFour.java,v 1.4 2005/10/06 04:24:17 rsdio Exp $
//
// Copyright (C) 2002, 2003 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.
//
// GNU Crypto is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// 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.
//
// As a special exception, the copyright holders of this library give
// you permission to link this library with independent modules to
// produce an executable, regardless of the license terms of these
// independent modules, and to copy and distribute the resulting
// executable under terms of your choice, provided that you also meet,
// for each linked independent module, the terms and conditions of the
// license of that module. An independent module is a module which is
// not derived from or based on this library. If you modify this
// library, you may extend this exception to your version of the
// library, but you are not obligated to do so. If you do not wish to
// do so, delete this exception statement from your version.
// ----------------------------------------------------------------------------
import gnu.crypto.Registry;
import java.util.Map;
/**
* RC4 is a stream cipher developed by Ron Rivest. Until 1994 RC4 was a
* trade secret of RSA Data Security, Inc., when it was released
* anonymously to a mailing list. This version is a descendent of that
* code, and since there is no proof that the leaked version was in fact
* RC4 and because "RC4" is a trademark, it is called "ARCFOUR", short for
* "Allegedly RC4".
*
* <p>This class only implements the <i>keystream</i> of ARCFOUR. To use
* this as a stream cipher, one would say:</p>
*
* <pre> out = in ^ arcfour.nextByte();</pre>
*
* <p>This operation works for encryption and decryption.</p>
*
* <p>References:</p>
*
* <ol>
* <li>Schneier, Bruce: <i>Applied Cryptography: Protocols, Algorithms,
* and Source Code in C, Second Edition.</i> (1996 John Wiley and Sons),
* pp. 397--398. ISBN 0-471-11709-9</li>
* <li>K. Kaukonen and R. Thayer, "A Stream Cipher Encryption Algorithm
* 'Arcfour'", Internet Draft (expired), <a
* href="http://www.mozilla.org/projects/security/pki/nss/draft-kaukonen-cipher-arcfour-03.txt">draft-kaukonen-cipher-arcfour-03.txt</a></li>
* </ol>
*
* @version $Revision: 1.4 $
*/
public class ARCFour extends BasePRNG implements Cloneable {
// Constants and variables.
// -----------------------------------------------------------------------
/** The attributes property name for the key bytes. */
public static final String ARCFOUR_KEY_MATERIAL =
"gnu.crypto.prng.arcfour.key-material";
/** The size of the internal S-box. */
public static final int ARCFOUR_SBOX_SIZE = 256;
/** The S-box. */
private byte[] s;
private byte m, n;
// Constructors.
// -----------------------------------------------------------------------
/** Default 0-arguments constructor. */
public ARCFour() {
super(Registry.ARCFOUR_PRNG);
}
// Methods implementing BasePRNG.
// -----------------------------------------------------------------------
public void setup(Map attributes) {
byte[] kb = (byte[]) attributes.get(ARCFOUR_KEY_MATERIAL);
if (kb == null) {
throw new IllegalArgumentException("ARCFOUR needs a key");
}
s = new byte[ARCFOUR_SBOX_SIZE];
m = n = 0;
byte[] k = new byte[ARCFOUR_SBOX_SIZE];
for (int i = 0; i < ARCFOUR_SBOX_SIZE; i++) {
s[i] = (byte) i;
}
if (kb.length > 0) {
for (int i = 0, j = 0; i < ARCFOUR_SBOX_SIZE; i++) {
k[i] = kb[j++];
if (j >= kb.length) j = 0;
}
}
for (int i = 0, j = 0; i < ARCFOUR_SBOX_SIZE; i++) {
j = j + s[i] + k[i];
byte temp = s[i];
s[i] = s[j & 0xff];
s[j & 0xff] = temp;
}
buffer = new byte[ARCFOUR_SBOX_SIZE];
try {
fillBlock();
} catch (LimitReachedException wontHappen) { }
}
public void fillBlock() throws LimitReachedException {
for (int i = 0; i < buffer.length; i++) {
m++;
n = (byte) (n + s[m & 0xff]);
byte temp = s[m & 0xff];
s[m & 0xff] = s[n & 0xff];
s[n & 0xff] = temp;
temp = (byte) (s[m & 0xff] + s[n & 0xff]);
buffer[i] = s[temp & 0xff];
}
}
}