Source for gnu.javax.crypto.key.dh.DiffieHellmanReceiver

   1: /* DiffieHellmanReceiver.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.key.dh;
  40: 
  41: import gnu.java.security.prng.IRandom;
  42: 
  43: import gnu.javax.crypto.key.KeyAgreementException;
  44: import gnu.javax.crypto.key.IncomingMessage;
  45: import gnu.javax.crypto.key.OutgoingMessage;
  46: 
  47: import java.math.BigInteger;
  48: import java.security.SecureRandom;
  49: import java.util.Map;
  50: 
  51: import javax.crypto.interfaces.DHPrivateKey;
  52: 
  53: /**
  54:  * This implementation is the receiver's part of the basic version of the
  55:  * Diffie-Hellman key agreement exchange (B in [HAC]).
  56:  *
  57:  * @see DiffieHellmanKeyAgreement
  58:  */
  59: public class DiffieHellmanReceiver
  60:     extends DiffieHellmanKeyAgreement
  61: {
  62:   private BigInteger y; // the receiver's random secret
  63: 
  64:   // default 0-arguments constructor
  65: 
  66:   protected void engineInit(Map attributes) throws KeyAgreementException
  67:   {
  68:     Object random = attributes.get(SOURCE_OF_RANDOMNESS);
  69:     rnd = null;
  70:     irnd = null;
  71:     if (random instanceof SecureRandom)
  72:       rnd = (SecureRandom) random;
  73:     else if (random instanceof IRandom)
  74:       irnd = (IRandom) random;
  75:     ownerKey = (DHPrivateKey) attributes.get(KA_DIFFIE_HELLMAN_OWNER_PRIVATE_KEY);
  76:     if (ownerKey == null)
  77:       throw new KeyAgreementException("missing owner's private key");
  78:   }
  79: 
  80:   protected OutgoingMessage engineProcessMessage(IncomingMessage in)
  81:       throws KeyAgreementException
  82:   {
  83:     switch (step)
  84:       {
  85:       case 0:
  86:         return computeSharedSecret(in);
  87:       default:
  88:         throw new IllegalStateException("unexpected state");
  89:       }
  90:   }
  91: 
  92:   private OutgoingMessage computeSharedSecret(IncomingMessage in)
  93:       throws KeyAgreementException
  94:   {
  95:     BigInteger m1 = in.readMPI();
  96:     if (m1 == null)
  97:       throw new KeyAgreementException("missing message (1)");
  98:     BigInteger p = ownerKey.getParams().getP();
  99:     BigInteger g = ownerKey.getParams().getG();
 100:     // B chooses a random integer y, 1 <= y <= p-2
 101:     // rfc-2631 restricts y to only be in [2, p-1]
 102:     BigInteger p_minus_2 = p.subtract(TWO);
 103:     byte[] xBytes = new byte[(p_minus_2.bitLength() + 7) / 8];
 104:     do
 105:       {
 106:         nextRandomBytes(xBytes);
 107:         y = new BigInteger(1, xBytes);
 108:       }
 109:     while (! (y.compareTo(TWO) >= 0 && y.compareTo(p_minus_2) <= 0));
 110:     ZZ = m1.modPow(y, p); // ZZ = (yb ^ xa) mod p
 111:     complete = true;
 112:     // B sends A the message: g^y mod p
 113:     OutgoingMessage result = new OutgoingMessage();
 114:     result.writeMPI(g.modPow(y, p)); // message (2)
 115:     return result;
 116:   }
 117: }