libjava/classpath/gnu/javax/crypto/key/srp6/SRP6User.java

   1 /* SRP6User.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.srp6;
  40
  41 import gnu.java.security.hash.IMessageDigest;
  42 import gnu.java.security.util.Util;
  43 import gnu.javax.crypto.key.KeyAgreementException;
  44 import gnu.javax.crypto.key.IncomingMessage;
  45 import gnu.javax.crypto.key.OutgoingMessage;
  46 import gnu.javax.crypto.sasl.srp.SRP;
  47
  48 import java.math.BigInteger;
  49 import java.security.KeyPair;
  50 import java.security.SecureRandom;
  51 import java.util.HashMap;
  52 import java.util.Map;
  53
  54 /**
  55  * <p>The implementation of the User in the SRP-6 protocol.</p>
  56  *
  57  * <p>Reference:</p>
  58  * <ol>
  59  *    <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
  60  *    Thomas J. Wu.</li>
  61  * </ol>
  62  */
  63 public class SRP6User extends SRP6KeyAgreement
  64 {
  65
  66   // Constants and variables
  67   // -------------------------------------------------------------------------
  68
  69   /** The user's identity. */
  70   private String I;
  71
  72   /** The user's cleartext password. */
  73   private byte[] p;
  74
  75   /** The user's ephemeral key pair. */
  76   private KeyPair userKeyPair;
  77
  78   // Constructor(s)
  79   // -------------------------------------------------------------------------
  80
  81   // default 0-arguments constructor
  82
  83   // Class methods
  84   // -------------------------------------------------------------------------
  85
  86   // Instance methods
  87   // -------------------------------------------------------------------------
  88
  89   // implementation of abstract methods in base class ------------------------
  90
  91   protected void engineInit(final Map attributes) throws KeyAgreementException
  92   {
  93     rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);
  94     N = (BigInteger) attributes.get(SHARED_MODULUS);
  95     if (N == null)
  96       {
  97         throw new KeyAgreementException("missing shared modulus");
  98       }
  99     g = (BigInteger) attributes.get(GENERATOR);
 100     if (g == null)
 101       {
 102         throw new KeyAgreementException("missing generator");
 103       }
 104
 105     final String md = (String) attributes.get(HASH_FUNCTION);
 106     if (md == null || "".equals(md.trim()))
 107       {
 108         throw new KeyAgreementException("missing hash function");
 109       }
 110     srp = SRP.instance(md);
 111
 112     I = (String) attributes.get(USER_IDENTITY);
 113     if (I == null)
 114       {
 115         throw new KeyAgreementException("missing user identity");
 116       }
 117     p = (byte[]) attributes.get(USER_PASSWORD);
 118     if (p == null)
 119       {
 120         throw new KeyAgreementException("missing user password");
 121       }
 122   }
 123
 124   protected OutgoingMessage engineProcessMessage(final IncomingMessage in)
 125       throws KeyAgreementException
 126   {
 127     switch (step)
 128       {
 129       case 0:
 130         return sendIdentity(in);
 131       case 1:
 132         return computeSharedSecret(in);
 133       default:
 134         throw new IllegalStateException("unexpected state");
 135       }
 136   }
 137
 138   protected void engineReset()
 139   {
 140     I = null;
 141     p = null;
 142     userKeyPair = null;
 143     super.engineReset();
 144   }
 145
 146   // own methods -------------------------------------------------------------
 147
 148   private OutgoingMessage sendIdentity(final IncomingMessage in)
 149       throws KeyAgreementException
 150   {
 151     // generate an ephemeral keypair
 152     final SRPKeyPairGenerator kpg = new SRPKeyPairGenerator();
 153     final Map attributes = new HashMap();
 154     if (rnd != null)
 155       {
 156         attributes.put(SRPKeyPairGenerator.SOURCE_OF_RANDOMNESS, rnd);
 157       }
 158     attributes.put(SRPKeyPairGenerator.SHARED_MODULUS, N);
 159     attributes.put(SRPKeyPairGenerator.GENERATOR, g);
 160     kpg.setup(attributes);
 161     userKeyPair = kpg.generate();
 162
 163     final OutgoingMessage result = new OutgoingMessage();
 164     result.writeString(I);
 165     result.writeMPI(((SRPPublicKey) userKeyPair.getPublic()).getY());
 166
 167     return result;
 168   }
 169
 170   private OutgoingMessage computeSharedSecret(final IncomingMessage in)
 171       throws KeyAgreementException
 172   {
 173     final BigInteger s = in.readMPI();
 174     final BigInteger B = in.readMPI();
 175
 176     final BigInteger A = ((SRPPublicKey) userKeyPair.getPublic()).getY();
 177     final BigInteger u = uValue(A, B); // u = H(A | B)
 178
 179     final BigInteger x;
 180     try
 181       {
 182         x = new BigInteger(1, srp.computeX(Util.trim(s), I, p));
 183       }
 184     catch (Exception e)
 185       {
 186         throw new KeyAgreementException("computeSharedSecret()", e);
 187       }
 188
 189     // compute S = (B - 3g^x) ^ (a + ux)
 190     final BigInteger a = ((SRPPrivateKey) userKeyPair.getPrivate()).getX();
 191     final BigInteger S = B.subtract(THREE.multiply(g.modPow(x, N))).modPow(
 192                                                                            a.add(u.multiply(x)),
 193                                                                            N);
 194
 195     final byte[] sBytes = Util.trim(S);
 196     final IMessageDigest hash = srp.newDigest();
 197     hash.update(sBytes, 0, sBytes.length);
 198     K = new BigInteger(1, hash.digest());
 199
 200     complete = true;
 201     return null;
 202   }
 203 }