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/* ARCFour.java --

   Copyright (C) 2002, 2003, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath 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 of the License, or (at

your option) any later version.

GNU Classpath 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 GNU Classpath; if not, write to the Free Software

Foundation, Inc., 51 Franklin St, 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.  */

package gnu.javax.crypto.prng;

import gnu.java.security.Registry;

import gnu.java.security.prng.BasePRNG;

import gnu.java.security.prng.LimitReachedException;

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:

 * <pre>

 * out = in ˆ arcfour.nextByte();

 * </pre>

 * <p>

 * This operation works for encryption and decryption.

 * <p>

 * References:

 * <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>

 */

public class ARCFour

    extends BasePRNG

    implements Cloneable

{

  /** 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;

  /** Default 0-arguments constructor. */

  public ARCFour()

  {

    super(Registry.ARCFOUR_PRNG);

  }

  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];

      }

  }

}