1 /* DiffieHellmanReceiver.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
35 obligated to do so. If you do not wish to do so, delete this
36 exception statement from your version. */
39 package gnu.javax.crypto.key.dh;
41 import gnu.java.security.prng.IRandom;
43 import gnu.javax.crypto.key.KeyAgreementException;
44 import gnu.javax.crypto.key.IncomingMessage;
45 import gnu.javax.crypto.key.OutgoingMessage;
47 import java.math.BigInteger;
48 import java.security.SecureRandom;
51 import javax.crypto.interfaces.DHPrivateKey;
54 * This implementation is the receiver's part of the basic version of the
55 * Diffie-Hellman key agreement exchange (B in [HAC]).
57 * @see DiffieHellmanKeyAgreement
59 public class DiffieHellmanReceiver
60 extends DiffieHellmanKeyAgreement
62 private BigInteger y; // the receiver's random secret
64 // default 0-arguments constructor
66 protected void engineInit(Map attributes) throws KeyAgreementException
68 Object random = attributes.get(SOURCE_OF_RANDOMNESS);
71 if (random instanceof SecureRandom)
72 rnd = (SecureRandom) random;
73 else if (random instanceof IRandom)
74 irnd = (IRandom) random;
75 ownerKey = (DHPrivateKey) attributes.get(KA_DIFFIE_HELLMAN_OWNER_PRIVATE_KEY);
77 throw new KeyAgreementException("missing owner's private key");
80 protected OutgoingMessage engineProcessMessage(IncomingMessage in)
81 throws KeyAgreementException
86 return computeSharedSecret(in);
88 throw new IllegalStateException("unexpected state");
92 private OutgoingMessage computeSharedSecret(IncomingMessage in)
93 throws KeyAgreementException
95 BigInteger m1 = in.readMPI();
97 throw new KeyAgreementException("missing message (1)");
98 BigInteger p = ownerKey.getParams().getP();
99 BigInteger g = ownerKey.getParams().getG();
100 // B chooses a random integer y, 1 <= y <= p-2
101 // rfc-2631 restricts y to only be in [2, p-1]
102 BigInteger p_minus_2 = p.subtract(TWO);
103 byte[] xBytes = new byte[(p_minus_2.bitLength() + 7) / 8];
106 nextRandomBytes(xBytes);
107 y = new BigInteger(1, xBytes);
109 while (! (y.compareTo(TWO) >= 0 && y.compareTo(p_minus_2) <= 0));
110 ZZ = m1.modPow(y, p); // ZZ = (yb ^ xa) mod p
112 // B sends A the message: g^y mod p
113 OutgoingMessage result = new OutgoingMessage();
114 result.writeMPI(g.modPow(y, p)); // message (2)