Source for gnu.java.security.provider.SHA1PRNG

   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: }