For the latest news and information visit
The GNU Crypto project

Class ElGamalKeyAgreement

  extended bygnu.crypto.key.BaseKeyAgreementParty
      extended bygnu.crypto.key.dh.ElGamalKeyAgreement
All Implemented Interfaces:
Direct Known 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.

$Revision: 1.2 $

Field Summary
static java.lang.String SOURCE_OF_RANDOMNESS
protected  java.math.BigInteger ZZ
          The shared secret key.
Fields inherited from class gnu.crypto.key.BaseKeyAgreementParty
complete, initialised, name, rnd, step, TWO
Constructor Summary
protected ElGamalKeyAgreement()
Method Summary
protected  void engineReset()
protected  byte[] engineSharedSecret()
Methods inherited from class gnu.crypto.key.BaseKeyAgreementParty
engineInit, engineProcessMessage, getSharedSecret, init, isComplete, name, nextRandomBytes, processMessage, reset
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail


public static final java.lang.String SOURCE_OF_RANDOMNESS
See Also:
Constant Field Values


public static final java.lang.String KA_ELGAMAL_RECIPIENT_PRIVATE_KEY
See Also:
Constant Field Values


public static final java.lang.String KA_ELGAMAL_RECIPIENT_PUBLIC_KEY
See Also:
Constant Field Values


protected java.math.BigInteger ZZ
The shared secret key.

Constructor Detail


protected ElGamalKeyAgreement()
Method Detail


protected byte[] engineSharedSecret()
                             throws KeyAgreementException
Specified by:
engineSharedSecret in class BaseKeyAgreementParty


protected void engineReset()
Specified by:
engineReset in class BaseKeyAgreementParty

For the latest news and information visit
The GNU Crypto project

Copyright © 2001, 2002, 2003 Free Software Foundation, Inc. All Rights Reserved.