package gnu.crypto.key.srp6;

// ----------------------------------------------------------------------------
// $Id: SRP6SaslClient.java,v 1.4 2005/10/06 04:24:16 rsdio Exp $
//
// Copyright (C) 2003 Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2, or (at your option)
// any later version.
//
// GNU Crypto is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; see the file COPYING.  If not, write to the
//
//    Free Software Foundation Inc.,
//    51 Franklin Street, Fifth Floor,
//    Boston, MA 02110-1301
//    USA
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
//
// As a special exception, the copyright holders of this library give
// you permission to link this library with independent modules to
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// independent modules, and to copy and distribute the resulting
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// for each linked independent module, the terms and conditions of the
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// ----------------------------------------------------------------------------

import gnu.crypto.hash.IMessageDigest;
import gnu.crypto.key.KeyAgreementException;
import gnu.crypto.key.IncomingMessage;
import gnu.crypto.key.OutgoingMessage;
import gnu.crypto.util.Util;

import java.math.BigInteger;

/**
 * <p>A variation of the SRP-6 protocol as used in the SASL-SRP mechanism, for
 * the User (client side).</p>
 *
 * <p>In this alternative, the exchange goes as follows:</p>
 * <pre>
 *    C -> S:  I                      (identifies self)
 *    S -> C:  N, g, s, B = 3v + g^b  (sends salt, b = random number)
 *    C -> S:  A = g^a                (a = random number)
 * </pre>
 *
 * <p>All elements are computed the same way as in the standard version.</p>
 *
 * <p>Reference:</p>
 * <ol>
 *    <li><a href="http://www.ietf.org/internet-drafts/draft-burdis-cat-srp-sasl-09.txt">
 *    Secure Remote Password Authentication Mechanism</a><br>
 *    K. Burdis, R. Naffah.</li>
 *    <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
 *    Thomas J. Wu.</li>
 * </ol>
 *
 * @version $Revision: 1.4 $
 */
public class SRP6SaslClient extends SRP6TLSClient {

   // Constants and variables
   // -------------------------------------------------------------------------

   // Constructor(s)
   // -------------------------------------------------------------------------

   // default 0-arguments constructor

   // Class methods
   // -------------------------------------------------------------------------

   // Instance methods
   // -------------------------------------------------------------------------

   protected OutgoingMessage computeSharedSecret(final IncomingMessage in)
   throws KeyAgreementException {
      final OutgoingMessage result = super.computeSharedSecret(in);

      final byte[] sBytes = Util.trim(K);
      final IMessageDigest hash = srp.newDigest();
      hash.update(sBytes, 0, sBytes.length);
      K = new BigInteger(1, hash.digest());

      return result;
   }
}
