Source for gnu.javax.crypto.sasl.srp.KDF

   1: /* KDF.java --
   2:    Copyright (C) 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.sasl.srp;
  40: 
  41: import gnu.java.security.Registry;
  42: import gnu.java.security.prng.LimitReachedException;
  43: import gnu.java.security.util.PRNG;
  44: import gnu.javax.crypto.cipher.IBlockCipher;
  45: import gnu.javax.crypto.prng.UMacGenerator;
  46: 
  47: import java.util.HashMap;
  48: 
  49: /**
  50:  * The SASL-SRP KDF implementation, which is also used, depending on how it was
  51:  * instantiated, as a secure Pseudo Random Number Generator.
  52:  */
  53: public class KDF
  54: {
  55:   private static final int AES_BLOCK_SIZE = 16; // default block size for AES
  56:   private static final int AES_KEY_SIZE = 16; // default key size for the AES
  57:   private static final byte[] buffer = new byte[1];
  58:   /** Our default source of randomness. */
  59:   private static final PRNG prng = PRNG.getInstance();
  60:   /** The underlying UMAC Generator instance. */
  61:   private UMacGenerator umac = null;
  62: 
  63:   /**
  64:    * Constructs an instance of the <code>KDF</code> initialised with the
  65:    * designated shared secret bytes.
  66:    *
  67:    * @param keyMaterial the SASL SRP shared secret (K) bytes.
  68:    */
  69:   private KDF(final byte[] keyMaterial, final int ndx)
  70:   {
  71:     super();
  72: 
  73:     final HashMap map = new HashMap();
  74:     map.put(UMacGenerator.CIPHER, Registry.AES_CIPHER);
  75:     map.put(UMacGenerator.INDEX, Integer.valueOf(ndx));
  76:     map.put(IBlockCipher.CIPHER_BLOCK_SIZE, Integer.valueOf(AES_BLOCK_SIZE));
  77:     final byte[] key = new byte[AES_KEY_SIZE];
  78:     System.arraycopy(keyMaterial, 0, key, 0, AES_KEY_SIZE);
  79:     map.put(IBlockCipher.KEY_MATERIAL, key);
  80:     umac = new UMacGenerator();
  81:     umac.init(map);
  82:   }
  83: 
  84:   /**
  85:    * A Factory mehod that returns an instance of a <code>KDF</code> based on
  86:    * supplied seed data.
  87:    *
  88:    * @param K the SASL SRP shared secret for a <code>KDF</code> to be used for
  89:    *          <i>CALG</i> and <i>IALG</i> setup. <code>null</code> otherwise.
  90:    * @return an instance of a <code>KDF</code>.
  91:    */
  92:   static final KDF getInstance(final byte[] K)
  93:   {
  94:     int ndx = -1;
  95:     final byte[] keyMaterial;
  96:     if (K != null)
  97:       {
  98:         keyMaterial = K;
  99:         ndx = 0;
 100:       }
 101:     else
 102:       {
 103:         keyMaterial = new byte[AES_BLOCK_SIZE];
 104:         while (ndx < 1 || ndx > 255)
 105:           ndx = (byte) nextByte();
 106:       }
 107:     return new KDF(keyMaterial, ndx);
 108:   }
 109: 
 110:   private static synchronized final int nextByte()
 111:   {
 112:     prng.nextBytes(buffer);
 113:     return (buffer[0] & 0xFF);
 114:   }
 115: 
 116:   /**
 117:    * Returns a designated number of bytes suitable for use in the SASL SRP
 118:    * mechanism.
 119:    *
 120:    * @param length the number of bytes needed.
 121:    * @return a byte array containing the generated/selected bytes.
 122:    */
 123:   public synchronized byte[] derive(final int length)
 124:   {
 125:     final byte[] result = new byte[length];
 126:     try
 127:       {
 128:         umac.nextBytes(result, 0, length);
 129:       }
 130:     catch (IllegalStateException x) // should not happen
 131:       {
 132:         x.printStackTrace(System.err);
 133:       }
 134:     catch (LimitReachedException x) // idem
 135:       {
 136:         x.printStackTrace(System.err);
 137:       }
 138:     return result;
 139:   }
 140: }