package gnu.crypto.key.srp6;
// ----------------------------------------------------------------------------
// $Id: SRP6User.java,v 1.3 2005/10/06 04:24:16 rsdio Exp $
//
// Copyright (C) 2003 Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto 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, or (at your option)
// any later version.
//
// GNU Crypto 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 this program; see the file COPYING. If not, write to the
//
// Free Software Foundation Inc.,
// 51 Franklin Street, 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
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// library, you may extend this exception to your version of the
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// do so, delete this exception statement from your version.
// ----------------------------------------------------------------------------
import gnu.crypto.hash.IMessageDigest;
import gnu.crypto.key.KeyAgreementException;
import gnu.crypto.key.IncomingMessage;
import gnu.crypto.key.OutgoingMessage;
import gnu.crypto.sasl.srp.SRP;
import gnu.crypto.util.Util;
import java.math.BigInteger;
import java.security.KeyPair;
import java.security.SecureRandom;
import java.util.HashMap;
import java.util.Map;
/**
* <p>The implementation of the User in the SRP-6 protocol.</p>
*
* <p>Reference:</p>
* <ol>
* <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
* Thomas J. Wu.</li>
* </ol>
*
* @version $Revision: 1.3 $
*/
public class SRP6User extends SRP6KeyAgreement {
// Constants and variables
// -------------------------------------------------------------------------
/** The user's identity. */
private String I;
/** The user's cleartext password. */
private byte[] p;
/** The user's ephemeral key pair. */
private KeyPair userKeyPair;
// Constructor(s)
// -------------------------------------------------------------------------
// default 0-arguments constructor
// Class methods
// -------------------------------------------------------------------------
// Instance methods
// -------------------------------------------------------------------------
// implementation of abstract methods in base class ------------------------
protected void engineInit(final Map attributes) throws KeyAgreementException {
rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);
N = (BigInteger) attributes.get(SHARED_MODULUS);
if (N == null) {
throw new KeyAgreementException("missing shared modulus");
}
g = (BigInteger) attributes.get(GENERATOR);
if (g == null) {
throw new KeyAgreementException("missing generator");
}
final String md = (String) attributes.get(HASH_FUNCTION);
if (md == null || "".equals(md.trim())) {
throw new KeyAgreementException("missing hash function");
}
srp = SRP.instance(md);
I = (String) attributes.get(USER_IDENTITY);
if (I == null) {
throw new KeyAgreementException("missing user identity");
}
p = (byte[]) attributes.get(USER_PASSWORD);
if (p == null) {
throw new KeyAgreementException("missing user password");
}
}
protected OutgoingMessage engineProcessMessage(final IncomingMessage in)
throws KeyAgreementException {
switch (step) {
case 0: return sendIdentity(in);
case 1: return computeSharedSecret(in);
default: throw new IllegalStateException("unexpected state");
}
}
protected void engineReset() {
I = null;
p = null;
userKeyPair = null;
super.engineReset();
}
// own methods -------------------------------------------------------------
private OutgoingMessage sendIdentity(final IncomingMessage in)
throws KeyAgreementException {
// generate an ephemeral keypair
final SRPKeyPairGenerator kpg = new SRPKeyPairGenerator();
final Map attributes = new HashMap();
if (rnd != null) {
attributes.put(SRPKeyPairGenerator.SOURCE_OF_RANDOMNESS, rnd);
}
attributes.put(SRPKeyPairGenerator.SHARED_MODULUS, N);
attributes.put(SRPKeyPairGenerator.GENERATOR, g);
kpg.setup(attributes);
userKeyPair = kpg.generate();
final OutgoingMessage result = new OutgoingMessage();
result.writeString(I);
result.writeMPI(((SRPPublicKey) userKeyPair.getPublic()).getY());
return result;
}
private OutgoingMessage computeSharedSecret(final IncomingMessage in)
throws KeyAgreementException {
final BigInteger s = in.readMPI();
final BigInteger B = in.readMPI();
final BigInteger A = ((SRPPublicKey) userKeyPair.getPublic()).getY();
final BigInteger u = uValue(A, B); // u = H(A | B)
final BigInteger x;
try {
x = new BigInteger(1, srp.computeX(Util.trim(s), I, p));
} catch (Exception e) {
throw new KeyAgreementException("computeSharedSecret()", e);
}
// compute S = (B - 3g^x) ^ (a + ux)
final BigInteger a = ((SRPPrivateKey) userKeyPair.getPrivate()).getX();
final BigInteger S = B.subtract(THREE.multiply(g.modPow(x, N)))
.modPow(a.add(u.multiply(x)), N);
final byte[] sBytes = Util.trim(S);
final IMessageDigest hash = srp.newDigest();
hash.update(sBytes, 0, sBytes.length);
K = new BigInteger(1, hash.digest());
complete = true;
return null;
}
}