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    */
SHA1PRNG()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 
engineSetSeed(byte[] seed)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 
engineNextBytes(byte[] bytes)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 
engineGenerateSeed(int numBytes)116   public byte[] engineGenerateSeed(int numBytes)
117   {
118     byte tmp[] = new byte[numBytes];
119 
120     engineNextBytes( tmp );
121     return tmp;
122   }
123 
ensureIsSeeded()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 }
138