| /* ElGamalKeyAgreement.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. |
| |
| 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 |
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| obligated to do so. If you do not wish to do so, delete this |
| exception statement from your version. */ |
| |
| |
| package gnu.javax.crypto.key.dh; |
| |
| import gnu.java.security.Registry; |
| import gnu.java.security.util.Util; |
| |
| import gnu.javax.crypto.key.BaseKeyAgreementParty; |
| import gnu.javax.crypto.key.KeyAgreementException; |
| |
| import java.math.BigInteger; |
| |
| /** |
| * 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: |
| * <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: |
| * <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: |
| * <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> |
| */ |
| public abstract class ElGamalKeyAgreement |
| extends BaseKeyAgreementParty |
| { |
| 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; |
| |
| protected ElGamalKeyAgreement() |
| { |
| super(Registry.ELGAMAL_KA); |
| } |
| |
| protected byte[] engineSharedSecret() throws KeyAgreementException |
| { |
| return Util.trim(ZZ); |
| } |
| |
| protected void engineReset() |
| { |
| ZZ = null; |
| } |
| } |