1 /* SRP6TLSClient.java --
2 Copyright (C) 2003, 2006 Free Software Foundation, Inc.
4 This file is a part of GNU Classpath.
6 GNU Classpath is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2 of the License, or (at
9 your option) any later version.
11 GNU Classpath is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GNU Classpath; if not, write to the Free Software
18 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
21 Linking this library statically or dynamically with other modules is
22 making a combined work based on this library. Thus, the terms and
23 conditions of the GNU General Public License cover the whole
26 As a special exception, the copyright holders of this library give you
27 permission to link this library with independent modules to produce an
28 executable, regardless of the license terms of these independent
29 modules, and to copy and distribute the resulting executable under
30 terms of your choice, provided that you also meet, for each linked
31 independent module, the terms and conditions of the license of that
32 module. An independent module is a module which is not derived from
33 or based on this library. If you modify this library, you may extend
34 this exception to your version of the library, but you are not
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36 exception statement from your version. */
39 package gnu.javax.crypto.key.srp6;
41 import gnu.java.security.util.Util;
42 import gnu.javax.crypto.key.KeyAgreementException;
43 import gnu.javax.crypto.key.IncomingMessage;
44 import gnu.javax.crypto.key.OutgoingMessage;
45 import gnu.javax.crypto.sasl.srp.SRP;
47 import java.math.BigInteger;
48 import java.security.KeyPair;
49 import java.security.SecureRandom;
50 import java.util.HashMap;
54 * A variation of the SRP6 key agreement protocol, for the client-side as
56 * href="http://www.ietf.org/internet-drafts/draft-ietf-tls-srp-05.txt">Using
57 * SRP for TLS Authentication</a>. The only difference between it and the SASL
58 * variant is that the shared secret is the entity <code>S</code> and not
61 public class SRP6TLSClient
62 extends SRP6KeyAgreement
64 /** The user's identity. */
66 /** The user's cleartext password. */
68 /** The user's ephemeral key pair. */
69 private KeyPair userKeyPair;
71 // default 0-arguments constructor
73 protected void engineInit(final Map attributes) throws KeyAgreementException
75 rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);
76 final String md = (String) attributes.get(HASH_FUNCTION);
77 if (md == null || md.trim().length() == 0)
78 throw new KeyAgreementException("missing hash function");
79 srp = SRP.instance(md);
80 I = (String) attributes.get(USER_IDENTITY);
82 throw new KeyAgreementException("missing user identity");
83 p = (byte[]) attributes.get(USER_PASSWORD);
85 throw new KeyAgreementException("missing user password");
88 protected OutgoingMessage engineProcessMessage(final IncomingMessage in)
89 throws KeyAgreementException
94 return sendIdentity(in);
96 return computeSharedSecret(in);
98 throw new IllegalStateException("unexpected state");
102 protected void engineReset()
110 private OutgoingMessage sendIdentity(final IncomingMessage in)
111 throws KeyAgreementException
113 final OutgoingMessage result = new OutgoingMessage();
114 result.writeString(I);
118 protected OutgoingMessage computeSharedSecret(final IncomingMessage in)
119 throws KeyAgreementException
123 final BigInteger s = in.readMPI();
124 final BigInteger B = in.readMPI();
125 // generate an ephemeral keypair
126 final SRPKeyPairGenerator kpg = new SRPKeyPairGenerator();
127 final Map attributes = new HashMap();
129 attributes.put(SRPKeyPairGenerator.SOURCE_OF_RANDOMNESS, rnd);
130 attributes.put(SRPKeyPairGenerator.SHARED_MODULUS, N);
131 attributes.put(SRPKeyPairGenerator.GENERATOR, g);
132 kpg.setup(attributes);
133 userKeyPair = kpg.generate();
134 final BigInteger A = ((SRPPublicKey) userKeyPair.getPublic()).getY();
135 final BigInteger u = uValue(A, B); // u = H(A | B)
139 x = new BigInteger(1, srp.computeX(Util.trim(s), I, p));
143 throw new KeyAgreementException("computeSharedSecret()", e);
145 // compute S = (B - 3g^x) ^ (a + ux)
146 final BigInteger a = ((SRPPrivateKey) userKeyPair.getPrivate()).getX();
147 final BigInteger S = B.subtract(THREE.multiply(g.modPow(x, N)))
148 .modPow(a.add(u.multiply(x)), N);
150 final OutgoingMessage result = new OutgoingMessage();