Class ElGamalKeyAgreement

Implemented Interfaces:
Known Direct Subclasses:
ElGamalReceiver, ElGamalSender

public abstract class ElGamalKeyAgreement
extends BaseKeyAgreementParty

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:

RFC-2631 describes an Ephemeral-Static Mode of operations with Diffie-Hellman keypairs as follows:

  "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."


  1. Diffie-Hellman Key Agreement Method
    Eric Rescorla.
  2. [HAC]: Handbook of Applied Cryptography.
    CRC Press, Inc. ISBN 0-8493-8523-7, 1997
    Menezes, A., van Oorschot, P. and S. Vanstone.

Field Summary

static String
static String
static String
protected BigInteger
The shared secret key.

Fields inherited from class gnu.javax.crypto.key.BaseKeyAgreementParty

TWO, complete, initialised, irnd, name, rnd, step

Constructor Summary


Method Summary

protected void
protected byte[]

Methods inherited from class gnu.javax.crypto.key.BaseKeyAgreementParty

engineInit, engineProcessMessage, engineReset, engineSharedSecret, getSharedSecret, init, isComplete, name, nextRandomBytes, processMessage, reset

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details


public static final String KA_ELGAMAL_RECIPIENT_PRIVATE_KEY
Field Value:


public static final String KA_ELGAMAL_RECIPIENT_PUBLIC_KEY
Field Value:


public static final String SOURCE_OF_RANDOMNESS
Field Value:


protected BigInteger ZZ
The shared secret key.

Constructor Details


protected ElGamalKeyAgreement()

Method Details


protected void engineReset()
engineReset in interface BaseKeyAgreementParty


protected byte[] engineSharedSecret()
            throws KeyAgreementException
engineSharedSecret in interface BaseKeyAgreementParty -- 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. You should have received a copy of the GNU General Public License along with GNU Classpath; if not, write to the Free Software 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 combination. 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 modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.