gcc/libjava/classpath/gnu/javax/crypto/prng/ARCFour.java

/* 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
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your option) any later version.

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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.

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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
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permission to link this library with independent modules to produce an
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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:</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>
 */
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];
      }
  }
}