2 Copyright (C) 2003, 2006 Free Software Foundation, Inc.
4 This file is a part of GNU Classpath.
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14 General Public License for more details.
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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
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31 independent module, the terms and conditions of the license of that
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36 exception statement from your version. */
39 package gnu.javax.crypto.key.srp6;
41 import gnu.java.security.Registry;
42 import gnu.java.security.hash.IMessageDigest;
43 import gnu.java.security.util.Util;
44 import gnu.javax.crypto.key.KeyAgreementException;
45 import gnu.javax.crypto.key.IncomingMessage;
46 import gnu.javax.crypto.key.OutgoingMessage;
47 import gnu.javax.crypto.sasl.srp.SRP;
48 import gnu.javax.crypto.sasl.srp.SRPAuthInfoProvider;
49 import gnu.javax.crypto.sasl.srp.SRPRegistry;
51 import java.io.IOException;
52 import java.math.BigInteger;
53 import java.security.KeyPair;
54 import java.security.SecureRandom;
55 import java.util.HashMap;
59 * The implementation of the Host in the SRP-6 key agreement protocol.
63 * <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
68 extends SRP6KeyAgreement
70 /** The user's ephemeral key pair. */
71 private KeyPair hostKeyPair;
73 /** The SRP password database. */
74 private SRPAuthInfoProvider passwordDB;
76 // default 0-arguments constructor
78 protected void engineInit(final Map attributes) throws KeyAgreementException
80 rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);
81 N = (BigInteger) attributes.get(SHARED_MODULUS);
83 throw new KeyAgreementException("missing shared modulus");
84 g = (BigInteger) attributes.get(GENERATOR);
86 throw new KeyAgreementException("missing generator");
87 final String md = (String) attributes.get(HASH_FUNCTION);
88 if (md == null || md.trim().length() == 0)
89 throw new KeyAgreementException("missing hash function");
90 srp = SRP.instance(md);
91 passwordDB = (SRPAuthInfoProvider) attributes.get(HOST_PASSWORD_DB);
92 if (passwordDB == null)
93 throw new KeyAgreementException("missing SRP password database");
96 protected OutgoingMessage engineProcessMessage(final IncomingMessage in)
97 throws KeyAgreementException
102 return computeSharedSecret(in);
104 throw new IllegalStateException("unexpected state");
108 protected void engineReset()
114 private OutgoingMessage computeSharedSecret(final IncomingMessage in)
115 throws KeyAgreementException
117 final String I = in.readString();
118 final BigInteger A = in.readMPI();
119 // get s and v for user identified by I
120 // ----------------------------------------------------------------------
121 final Map credentials;
124 final Map userID = new HashMap();
125 userID.put(Registry.SASL_USERNAME, I);
126 userID.put(SRPRegistry.MD_NAME_FIELD, srp.getAlgorithm());
127 credentials = passwordDB.lookup(userID);
129 catch (IOException x)
131 throw new KeyAgreementException("computeSharedSecret()", x);
133 final BigInteger s = new BigInteger(
134 1,Util.fromBase64((String) credentials.get(SRPRegistry.SALT_FIELD)));
135 final BigInteger v = new BigInteger(
136 1, Util.fromBase64((String) credentials.get(SRPRegistry.USER_VERIFIER_FIELD)));
137 final SRPKeyPairGenerator kpg = new SRPKeyPairGenerator();
138 final Map attributes = new HashMap();
140 attributes.put(SRPKeyPairGenerator.SOURCE_OF_RANDOMNESS, rnd);
141 attributes.put(SRPKeyPairGenerator.SHARED_MODULUS, N);
142 attributes.put(SRPKeyPairGenerator.GENERATOR, g);
143 attributes.put(SRPKeyPairGenerator.USER_VERIFIER, v);
144 kpg.setup(attributes);
145 hostKeyPair = kpg.generate();
146 final BigInteger B = ((SRPPublicKey) hostKeyPair.getPublic()).getY();
147 final BigInteger u = uValue(A, B); // u = H(A | B)
148 // compute S = (Av^u) ^ b
149 final BigInteger b = ((SRPPrivateKey) hostKeyPair.getPrivate()).getX();
150 final BigInteger S = A.multiply(v.modPow(u, N)).modPow(b, N);
151 final byte[] sBytes = Util.trim(S);
152 final IMessageDigest hash = srp.newDigest();
153 hash.update(sBytes, 0, sBytes.length);
154 K = new BigInteger(1, hash.digest());
155 final OutgoingMessage result = new OutgoingMessage();