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

   1 /* ARCFour.java --
   2    Copyright (C) 2002, 2003, 2006 Free Software Foundation, Inc.
   3
   4 This file is a part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2 of the License, or (at
   9 your option) any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; if not, write to the Free Software
  18 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
  19 USA
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version.  */
  37
  38
  39 package gnu.javax.crypto.prng;
  40
  41 import gnu.java.security.Registry;
  42 import gnu.java.security.prng.BasePRNG;
  43 import gnu.java.security.prng.LimitReachedException;
  44
  45 import java.util.Map;
  46
  47 /**
  48  * RC4 is a stream cipher developed by Ron Rivest. Until 1994 RC4 was a
  49  * trade secret of RSA Data Security, Inc., when it was released
  50  * anonymously to a mailing list. This version is a descendent of that
  51  * code, and since there is no proof that the leaked version was in fact
  52  * RC4 and because "RC4" is a trademark, it is called "ARCFOUR", short for
  53  * "Allegedly RC4".
  54  *
  55  * <p>This class only implements the <i>keystream</i> of ARCFOUR. To use
  56  * this as a stream cipher, one would say:</p>
  57  *
  58  * <pre>    out = in ^ arcfour.nextByte();</pre>
  59  *
  60  * <p>This operation works for encryption and decryption.</p>
  61  *
  62  * <p>References:</p>
  63  *
  64  * <ol>
  65  * <li>Schneier, Bruce: <i>Applied Cryptography: Protocols, Algorithms,
  66  * and Source Code in C, Second Edition.</i> (1996 John Wiley and Sons),
  67  * pp. 397--398. ISBN 0-471-11709-9</li>
  68  * <li>K. Kaukonen and R. Thayer, "A Stream Cipher Encryption Algorithm
  69  * 'Arcfour'", Internet Draft (expired), <a
  70  * href="http://www.mozilla.org/projects/security/pki/nss/draft-kaukonen-cipher-arcfour-03.txt">draft-kaukonen-cipher-arcfour-03.txt</a></li>
  71  * </ol>
  72  */
  73 public class ARCFour extends BasePRNG implements Cloneable
  74 {
  75
  76   // Constants and variables.
  77   // -----------------------------------------------------------------------
  78
  79   /** The attributes property name for the key bytes. */
  80   public static final String ARCFOUR_KEY_MATERIAL = "gnu.crypto.prng.arcfour.key-material";
  81
  82   /** The size of the internal S-box. */
  83   public static final int ARCFOUR_SBOX_SIZE = 256;
  84
  85   /** The S-box. */
  86   private byte[] s;
  87
  88   private byte m, n;
  89
  90   // Constructors.
  91   // -----------------------------------------------------------------------
  92
  93   /** Default 0-arguments constructor. */
  94   public ARCFour()
  95   {
  96     super(Registry.ARCFOUR_PRNG);
  97   }
  98
  99   // Methods implementing BasePRNG.
 100   // -----------------------------------------------------------------------
 101
 102   public void setup(Map attributes)
 103   {
 104     byte[] kb = (byte[]) attributes.get(ARCFOUR_KEY_MATERIAL);
 105
 106     if (kb == null)
 107       {
 108         throw new IllegalArgumentException("ARCFOUR needs a key");
 109       }
 110
 111     s = new byte[ARCFOUR_SBOX_SIZE];
 112     m = n = 0;
 113     byte[] k = new byte[ARCFOUR_SBOX_SIZE];
 114
 115     for (int i = 0; i < ARCFOUR_SBOX_SIZE; i++)
 116       {
 117         s[i] = (byte) i;
 118       }
 119
 120     if (kb.length > 0)
 121       {
 122         for (int i = 0, j = 0; i < ARCFOUR_SBOX_SIZE; i++)
 123           {
 124             k[i] = kb[j++];
 125             if (j >= kb.length)
 126               j = 0;
 127           }
 128       }
 129
 130     for (int i = 0, j = 0; i < ARCFOUR_SBOX_SIZE; i++)
 131       {
 132         j = j + s[i] + k[i];
 133         byte temp = s[i];
 134         s[i] = s[j & 0xff];
 135         s[j & 0xff] = temp;
 136       }
 137
 138     buffer = new byte[ARCFOUR_SBOX_SIZE];
 139     try
 140       {
 141         fillBlock();
 142       }
 143     catch (LimitReachedException wontHappen)
 144       {
 145       }
 146   }
 147
 148   public void fillBlock() throws LimitReachedException
 149   {
 150     for (int i = 0; i < buffer.length; i++)
 151       {
 152         m++;
 153         n = (byte) (n + s[m & 0xff]);
 154         byte temp = s[m & 0xff];
 155         s[m & 0xff] = s[n & 0xff];
 156         s[n & 0xff] = temp;
 157         temp = (byte) (s[m & 0xff] + s[n & 0xff]);
 158         buffer[i] = s[temp & 0xff];
 159       }
 160   }
 161 }