gnu.crypto.key.dh
Class ElGamalKeyAgreement

java.lang.Object
  gnu.crypto.key.BaseKeyAgreementParty
      gnu.crypto.key.dh.ElGamalKeyAgreement

All Implemented Interfaces:

IKeyAgreementParty

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:

• A sends to B a single message allowing one-pass key agreement.
• A obtains an authentic copy of B's public key (p, g, yb), where yb = g**xb.
• 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.
• B computes the same key K on receipt of the previous message as (g**x)**xb.

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."
 

Reference:

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.

Version:

$Revision: 1.2 $

Field Summary

static java.lang.String	KA_ELGAMAL_RECIPIENT_PRIVATE_KEY
static java.lang.String	KA_ELGAMAL_RECIPIENT_PUBLIC_KEY
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

SOURCE_OF_RANDOMNESS

public static final java.lang.String SOURCE_OF_RANDOMNESS

See Also:

Constant Field Values

KA_ELGAMAL_RECIPIENT_PRIVATE_KEY

public static final java.lang.String KA_ELGAMAL_RECIPIENT_PRIVATE_KEY

See Also:

Constant Field Values

KA_ELGAMAL_RECIPIENT_PUBLIC_KEY

public static final java.lang.String KA_ELGAMAL_RECIPIENT_PUBLIC_KEY

See Also:

Constant Field Values

ZZ

protected java.math.BigInteger ZZ

The shared secret key.

Constructor Detail

ElGamalKeyAgreement

protected ElGamalKeyAgreement()

Method Detail

engineSharedSecret

protected byte[] engineSharedSecret()
                             throws KeyAgreementException

Specified by:

engineSharedSecret in class BaseKeyAgreementParty

Throws:

KeyAgreementException

engineReset

protected void engineReset()

Specified by:

engineReset in class BaseKeyAgreementParty