package gnu.crypto.key.dh;
// ----------------------------------------------------------------------------
// $Id: ElGamalKeyAgreement.java,v 1.2 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
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// you permission to link this library with independent modules to
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// do so, delete this exception statement from your version.
// ----------------------------------------------------------------------------
import gnu.crypto.Registry;
import gnu.crypto.key.BaseKeyAgreementParty;
import gnu.crypto.key.KeyAgreementException;
import gnu.crypto.util.Util;
import java.math.BigInteger;
/**
* <p>The ElGamal key agreement, also known as the half-certified Diffie-Hellman
* key agreement, is described in the Handbook of Applied Cryptography [HAC] as
* follows:</p>
* <ul>
* <li>A sends to B a single message allowing one-pass key agreement.</li>
* <li>A obtains an authentic copy of B's public key (p, g, yb), where
* yb = g**xb.</li>
* <li>A chooses a random integer x, 1 <= x <= p-2, and sends B the
* message g**x. A computes the shared secret key K as yb**x.</li>
* <li>B computes the same key K on receipt of the previous message as
* (g**x)**xb.</li>
* </ul>
*
* <p>RFC-2631 describes an <i>Ephemeral-Static Mode</i> of operations with
* Diffie-Hellman keypairs as follows:</p>
* <pre>
* "In Ephemeral-Static mode, the recipient has a static (and certified)
* key pair, but the sender generates a new key pair for each message
* and sends it using the originatorKey production. If the sender's key
* is freshly generated for each message, the shared secret ZZ will be
* similarly different for each message and partyAInfo MAY be omitted,
* since it serves merely to decouple multiple KEKs generated by the
* same set of pairwise keys. If, however, the same ephemeral sender key
* is used for multiple messages (e.g. it is cached as a performance
* optimization) then a separate partyAInfo MUST be used for each
* message. All implementations of this standard MUST implement
* Ephemeral-Static mode."
* </pre>
*
* <p>Reference:</p>
* <ol>
* <li><a href="http://www.ietf.org/rfc/rfc2631.txt">Diffie-Hellman Key
* Agreement Method</a><br>
* Eric Rescorla.</li>
* <li><a href="http://www.cacr.math.uwaterloo.ca/hac">[HAC]</a>: Handbook of
* Applied Cryptography.<br>
* CRC Press, Inc. ISBN 0-8493-8523-7, 1997<br>
* Menezes, A., van Oorschot, P. and S. Vanstone.</li>
* </ol>
*
* @version $Revision: 1.2 $
*/
public abstract class ElGamalKeyAgreement extends BaseKeyAgreementParty {
// Constants and variables
// -------------------------------------------------------------------------
public static final String SOURCE_OF_RANDOMNESS = "gnu.crypto.elgamal.ka.prng";
public static final String KA_ELGAMAL_RECIPIENT_PRIVATE_KEY =
"gnu.crypto.elgamal.ka.recipient.private.key";
public static final String KA_ELGAMAL_RECIPIENT_PUBLIC_KEY =
"gnu.crypto.elgamal.ka.recipient.public.key";
/** The shared secret key. */
protected BigInteger ZZ;
// Constructor(s)
// -------------------------------------------------------------------------
protected ElGamalKeyAgreement() {
super(Registry.ELGAMAL_KA);
}
// Class methods
// -------------------------------------------------------------------------
// Instance methods
// -------------------------------------------------------------------------
// implementation of common abstract methods in BaseKeyAGreementParty ------
protected byte[] engineSharedSecret() throws KeyAgreementException {
return Util.trim(ZZ);
}
protected void engineReset() {
ZZ = null;
}
}