mirror of git://gcc.gnu.org/git/gcc.git
113 lines
3.8 KiB
Java
113 lines
3.8 KiB
Java
/* ElGamalSender.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
|
|
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. */
|
|
|
|
|
|
package gnu.javax.crypto.key.dh;
|
|
|
|
import gnu.javax.crypto.key.KeyAgreementException;
|
|
import gnu.javax.crypto.key.IncomingMessage;
|
|
import gnu.javax.crypto.key.OutgoingMessage;
|
|
|
|
import java.math.BigInteger;
|
|
import java.security.SecureRandom;
|
|
import java.util.Map;
|
|
|
|
import javax.crypto.interfaces.DHPublicKey;
|
|
|
|
/**
|
|
* This implementation is the sender's part of the ElGamal key agreement
|
|
* exchange (A in [HAC]).
|
|
*
|
|
* @see ElGamalKeyAgreement
|
|
*/
|
|
public class ElGamalSender
|
|
extends ElGamalKeyAgreement
|
|
{
|
|
/** The recipient's public key. */
|
|
private DHPublicKey B;
|
|
|
|
// default 0-arguments constructor
|
|
|
|
protected void engineInit(Map attributes) throws KeyAgreementException
|
|
{
|
|
rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);
|
|
// One-time setup (key generation and publication). Each user B generates
|
|
// a keypair and publishes its public key
|
|
B = (DHPublicKey) attributes.get(KA_ELGAMAL_RECIPIENT_PUBLIC_KEY);
|
|
if (B == null)
|
|
throw new KeyAgreementException("missing recipient public key");
|
|
}
|
|
|
|
protected OutgoingMessage engineProcessMessage(IncomingMessage in)
|
|
throws KeyAgreementException
|
|
{
|
|
switch (step)
|
|
{
|
|
case 0:
|
|
return computeSharedSecret(in);
|
|
default:
|
|
throw new IllegalStateException("unexpected state");
|
|
}
|
|
}
|
|
|
|
private OutgoingMessage computeSharedSecret(IncomingMessage in)
|
|
throws KeyAgreementException
|
|
{
|
|
BigInteger p = B.getParams().getP();
|
|
BigInteger g = B.getParams().getG();
|
|
BigInteger yb = B.getY();
|
|
// A chooses a random integer x, 1 <= x <= p-2
|
|
// rfc-2631 restricts x to only be in [2, p-1]
|
|
BigInteger p_minus_2 = p.subtract(TWO);
|
|
byte[] xBytes = new byte[(p_minus_2.bitLength() + 7) / 8];
|
|
BigInteger x;
|
|
do
|
|
{
|
|
nextRandomBytes(xBytes);
|
|
x = new BigInteger(1, xBytes);
|
|
}
|
|
while (x.compareTo(TWO) >= 0 && x.compareTo(p_minus_2) <= 0);
|
|
// A sends B the message: g^x mod p
|
|
OutgoingMessage result = new OutgoingMessage();
|
|
result.writeMPI(g.modPow(x, p));
|
|
// A computes the key as K = (yb)^x mod p
|
|
ZZ = yb.modPow(x, p); // ZZ = (yb ^ xa) mod p
|
|
complete = true;
|
|
return result;
|
|
}
|
|
}
|