Source for gnu.java.security.prng.MDGenerator

   1: /* MDGenerator.java --
   2:    Copyright (C) 2001, 2002, 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.java.security.prng;
  40: 
  41: import gnu.java.security.Registry;
  42: import gnu.java.security.hash.HashFactory;
  43: import gnu.java.security.hash.IMessageDigest;
  44: 
  45: import java.util.Map;
  46: 
  47: /**
  48:  * A simple pseudo-random number generator that relies on a hash algorithm, that
  49:  * (a) starts its operation by hashing a <code>seed</code>, and then (b)
  50:  * continuously re-hashing its output. If no hash algorithm name is specified in
  51:  * the {@link Map} of attributes used to initialise the instance then the
  52:  * SHA-160 algorithm is used as the underlying hash function. Also, if no
  53:  * <code>seed</code> is given, an empty octet sequence is used.
  54:  */
  55: public class MDGenerator
  56:     extends BasePRNG
  57:     implements Cloneable
  58: {
  59:   /** Property name of underlying hash algorithm for this generator. */
  60:   public static final String MD_NAME = "gnu.crypto.prng.md.hash.name";
  61: 
  62:   /** Property name of seed material. */
  63:   public static final String SEEED = "gnu.crypto.prng.md.seed";
  64: 
  65:   /** The underlying hash instance. */
  66:   private IMessageDigest md;
  67: 
  68:   /** Trivial 0-arguments constructor. */
  69:   public MDGenerator()
  70:   {
  71:     super(Registry.MD_PRNG);
  72:   }
  73: 
  74:   public void setup(Map attributes)
  75:   {
  76:     // find out which hash to use
  77:     String underlyingMD = (String) attributes.get(MD_NAME);
  78:     if (underlyingMD == null)
  79:       {
  80:         if (md == null)
  81:           { // happy birthday
  82:             // ensure we have a reliable implementation of this hash
  83:             md = HashFactory.getInstance(Registry.SHA160_HASH);
  84:           }
  85:         else // a clone. reset it for reuse
  86:           md.reset();
  87:       }
  88:     else // ensure we have a reliable implementation of this hash
  89:       md = HashFactory.getInstance(underlyingMD);
  90:     // get the seeed
  91:     byte[] seed = (byte[]) attributes.get(SEEED);
  92:     if (seed == null)
  93:       seed = new byte[0];
  94: 
  95:     md.update(seed, 0, seed.length);
  96:   }
  97: 
  98:   public void fillBlock() throws LimitReachedException
  99:   {
 100:     IMessageDigest mdc = (IMessageDigest) md.clone();
 101:     buffer = mdc.digest();
 102:     md.update(buffer, 0, buffer.length);
 103:   }
 104: 
 105:   public void addRandomByte(final byte b)
 106:   {
 107:     if (md == null)
 108:       throw new IllegalStateException("not initialized");
 109:     md.update(b);
 110:   }
 111: 
 112:   public void addRandomBytes(final byte[] buf, final int off, final int len)
 113:   {
 114:     if (md == null)
 115:       throw new IllegalStateException("not initialized");
 116:     md.update(buf, off, len);
 117:   }
 118: 
 119:   public Object clone() throws CloneNotSupportedException
 120:   {
 121:     MDGenerator result = (MDGenerator) super.clone();
 122:     if (this.md != null)
 123:       result.md = (IMessageDigest) this.md.clone();
 124: 
 125:     return result;
 126:   }
 127: }