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/* SRP6SaslClient.java --

   Copyright (C) 2003, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath 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 of the License, or (at

your option) any later version.

GNU Classpath 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.

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Foundation, Inc., 51 Franklin St, 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

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As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

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package gnu.javax.crypto.key.srp6;

import gnu.java.security.hash.IMessageDigest;

import gnu.java.security.util.Util;

import gnu.javax.crypto.key.KeyAgreementException;

import gnu.javax.crypto.key.IncomingMessage;

import gnu.javax.crypto.key.OutgoingMessage;

import java.math.BigInteger;

/**

 * A variation of the SRP-6 protocol as used in the SASL-SRP mechanism, for the

 * User (client side).

 * <p>

 * In this alternative, the exchange goes as follows:

 *

 * <pre>

 *     C -> S:  I                      (identifies self)

 *     S -> C:  N, g, s, B = 3v + gˆb  (sends salt, b = random number)

 *     C -> S:  A = gˆa                (a = random number)

 * </pre>

 *

 * <p>

 * All elements are computed the same way as in the standard version.

 * <p>

 * Reference:

 * <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>

 */

public class SRP6SaslClient

    extends SRP6TLSClient

{

  // default 0-arguments constructor

  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;

  }

}