gomp-20050608-branch/libjava/classpath/gnu/java/security/provider/SHA1PRNG.java

   1 /* SHA1PRNG.java --- Secure Random SPI SHA1PRNG
   2    Copyright (C) 1999, 2001, 2003, 2005 Free Software Foundation, Inc.
   3
   4 This file is 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, or (at your option)
   9 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; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 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.java.security.provider;
  40
  41 import java.io.Serializable;
  42 import java.security.MessageDigest;
  43 import java.security.NoSuchAlgorithmException;
  44 import java.security.SecureRandomSpi;
  45 import java.util.Random;
  46
  47 public class SHA1PRNG extends SecureRandomSpi implements Serializable
  48 {
  49   MessageDigest digest;
  50   byte seed[];
  51   byte data[];
  52   int seedpos;
  53   int datapos;
  54   private boolean seeded = false; // set to true when we seed this
  55   /**
  56    * The size of seed.
  57    */
  58   private static final int SEED_SIZE = 20;
  59   /**
  60    * The size of data.
  61    */
  62   private static final int DATA_SIZE = 40;
  63
  64   /**
  65    * Create a new SHA-1 pseudo-random number generator.
  66    */
  67   public SHA1PRNG()
  68   {
  69     try {
  70       digest = MessageDigest.getInstance("SHA");
  71     } catch ( NoSuchAlgorithmException nsae) {
  72 //      System.out.println("Failed to find SHA Message Digest: " + nsae);
  73 //      nsae.printStackTrace();
  74       throw new InternalError ("no SHA implementation found");
  75     }
  76
  77     seed = new byte[SEED_SIZE];
  78     seedpos = 0;
  79     data = new byte[DATA_SIZE];
  80     datapos = SEED_SIZE;  // try to force hashing a first block
  81   }
  82
  83   public void engineSetSeed(byte[] seed)
  84   {
  85     for(int i = 0; i < seed.length; i++)
  86       this.seed[seedpos++ % SEED_SIZE] ^= seed[i];
  87     seedpos %= SEED_SIZE;
  88
  89   }
  90
  91   public void engineNextBytes(byte[] bytes)
  92   {
  93     ensureIsSeeded ();
  94     int loc = 0;
  95     while (loc < bytes.length)
  96       {
  97         int copy = Math.min (bytes.length - loc, SEED_SIZE - datapos);
  98
  99         if (copy > 0)
 100           {
 101             System.arraycopy (data, datapos, bytes, loc, copy);
 102             datapos += copy;
 103             loc += copy;
 104           }
 105         else
 106           {
 107             // No data ready for copying, so refill our buffer.
 108             System.arraycopy( seed, 0, data, SEED_SIZE, SEED_SIZE);
 109             byte[] digestdata = digest.digest( data );
 110             System.arraycopy( digestdata, 0, data, 0, SEED_SIZE);
 111             datapos = 0;
 112           }
 113       }
 114   }
 115
 116   public byte[] engineGenerateSeed(int numBytes)
 117   {
 118     byte tmp[] = new byte[numBytes];
 119
 120     engineNextBytes( tmp );
 121     return tmp;
 122   }
 123
 124   private void ensureIsSeeded()
 125   {
 126     if (!seeded)
 127       {
 128         new Random(0L).nextBytes(seed);
 129
 130         byte[] digestdata = digest.digest(data);
 131         System.arraycopy(digestdata, 0, data, 0, SEED_SIZE);
 132
 133         seeded = true;
 134       }
 135   }
 136
 137 }