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Copyright (C) 2003, 2006 Free Software Foundation, Inc.
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This file is a part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at
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your option) any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package gnu.javax.crypto.key.srp6;
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import gnu.java.security.hash.IMessageDigest;
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import gnu.java.security.util.Util;
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import gnu.javax.crypto.key.KeyAgreementException;
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import gnu.javax.crypto.key.IncomingMessage;
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import gnu.javax.crypto.key.OutgoingMessage;
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import gnu.javax.crypto.sasl.srp.SRP;
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import java.math.BigInteger;
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import java.security.KeyPair;
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import java.security.SecureRandom;
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import java.util.HashMap;
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* <p>The implementation of the User in the SRP-6 protocol.</p>
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* <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
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public class SRP6User extends SRP6KeyAgreement
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// Constants and variables
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// -------------------------------------------------------------------------
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/** The user's identity. */
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/** The user's cleartext password. */
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/** The user's ephemeral key pair. */
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private KeyPair userKeyPair;
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// -------------------------------------------------------------------------
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// default 0-arguments constructor
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// -------------------------------------------------------------------------
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// -------------------------------------------------------------------------
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// implementation of abstract methods in base class ------------------------
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protected void engineInit(final Map attributes) throws KeyAgreementException
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rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);
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N = (BigInteger) attributes.get(SHARED_MODULUS);
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throw new KeyAgreementException("missing shared modulus");
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g = (BigInteger) attributes.get(GENERATOR);
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throw new KeyAgreementException("missing generator");
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final String md = (String) attributes.get(HASH_FUNCTION);
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if (md == null || "".equals(md.trim()))
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throw new KeyAgreementException("missing hash function");
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srp = SRP.instance(md);
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I = (String) attributes.get(USER_IDENTITY);
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throw new KeyAgreementException("missing user identity");
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p = (byte[]) attributes.get(USER_PASSWORD);
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throw new KeyAgreementException("missing user password");
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protected OutgoingMessage engineProcessMessage(final IncomingMessage in)
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throws KeyAgreementException
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return sendIdentity(in);
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return computeSharedSecret(in);
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throw new IllegalStateException("unexpected state");
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protected void engineReset()
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// own methods -------------------------------------------------------------
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private OutgoingMessage sendIdentity(final IncomingMessage in)
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throws KeyAgreementException
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// generate an ephemeral keypair
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final SRPKeyPairGenerator kpg = new SRPKeyPairGenerator();
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final Map attributes = new HashMap();
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attributes.put(SRPKeyPairGenerator.SOURCE_OF_RANDOMNESS, rnd);
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attributes.put(SRPKeyPairGenerator.SHARED_MODULUS, N);
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attributes.put(SRPKeyPairGenerator.GENERATOR, g);
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kpg.setup(attributes);
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userKeyPair = kpg.generate();
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final OutgoingMessage result = new OutgoingMessage();
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result.writeString(I);
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result.writeMPI(((SRPPublicKey) userKeyPair.getPublic()).getY());
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private OutgoingMessage computeSharedSecret(final IncomingMessage in)
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throws KeyAgreementException
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final BigInteger s = in.readMPI();
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final BigInteger B = in.readMPI();
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final BigInteger A = ((SRPPublicKey) userKeyPair.getPublic()).getY();
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final BigInteger u = uValue(A, B); // u = H(A | B)
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x = new BigInteger(1, srp.computeX(Util.trim(s), I, p));
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throw new KeyAgreementException("computeSharedSecret()", e);
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// compute S = (B - 3g^x) ^ (a + ux)
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final BigInteger a = ((SRPPrivateKey) userKeyPair.getPrivate()).getX();
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final BigInteger S = B.subtract(THREE.multiply(g.modPow(x, N))).modPow(
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a.add(u.multiply(x)),
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final byte[] sBytes = Util.trim(S);
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final IMessageDigest hash = srp.newDigest();
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hash.update(sBytes, 0, sBytes.length);
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K = new BigInteger(1, hash.digest());