1 /* SRPKeyPairGenerator.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.srp6;
41 import gnu.java.security.Configuration;
42 import gnu.java.security.Registry;
43 import gnu.java.security.key.IKeyPairGenerator;
44 import gnu.java.security.util.PRNG;
46 import java.math.BigInteger;
47 import java.security.KeyPair;
48 import java.security.SecureRandom;
50 import java.util.logging.Logger;
55 * <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
59 public class SRPKeyPairGenerator
60 implements IKeyPairGenerator
62 private static final Logger log = Logger.getLogger(SRPKeyPairGenerator.class.getName());
63 private static final BigInteger ZERO = BigInteger.ZERO;
64 private static final BigInteger ONE = BigInteger.ONE;
65 private static final BigInteger TWO = BigInteger.valueOf(2L);
66 private static final BigInteger THREE = BigInteger.valueOf(3L);
67 /** Property name of the length (Integer) of the modulus (N) of an SRP key. */
68 public static final String MODULUS_LENGTH = "gnu.crypto.srp.L";
69 /** Property name of the Boolean indicating wether or not to use defaults. */
70 public static final String USE_DEFAULTS = "gnu.crypto.srp.use.defaults";
71 /** Property name of the modulus (N) of an SRP key. */
72 public static final String SHARED_MODULUS = "gnu.crypto.srp.N";
73 /** Property name of the generator (g) of an SRP key. */
74 public static final String GENERATOR = "gnu.crypto.srp.g";
75 /** Property name of the user's verifier (v) for a Server SRP key. */
76 public static final String USER_VERIFIER = "gnu.crypto.srp.v";
78 * Property name of an optional {@link SecureRandom} instance to use. The
79 * default is to use a classloader singleton from {@link PRNG}.
81 public static final String SOURCE_OF_RANDOMNESS = "gnu.crypto.srp.prng";
82 /** Default value for the modulus length. */
83 private static final int DEFAULT_MODULUS_LENGTH = 1024;
84 /** The optional {@link SecureRandom} instance to use. */
85 private SecureRandom rnd = null;
86 /** Bit length of the shared modulus. */
88 /** The shared public modulus. */
90 /** The Field generator. */
92 /** The user's verifier MPI. */
94 /** Our default source of randomness. */
95 private PRNG prng = null;
97 // implicit 0-arguments constructor
101 return Registry.SRP_KPG;
104 public void setup(Map attributes)
106 // do we have a SecureRandom, or should we use our own?
107 rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);
108 N = (BigInteger) attributes.get(SHARED_MODULUS);
112 g = (BigInteger) attributes.get(GENERATOR);
115 SRPAlgorithm.checkParams(N, g);
118 { // generate or use default values for N and g
119 Boolean useDefaults = (Boolean) attributes.get(USE_DEFAULTS);
120 if (useDefaults == null)
121 useDefaults = Boolean.TRUE;
122 Integer L = (Integer) attributes.get(MODULUS_LENGTH);
123 l = DEFAULT_MODULUS_LENGTH;
124 if (useDefaults.equals(Boolean.TRUE))
132 N = SRPAlgorithm.N_512;
135 N = SRPAlgorithm.N_640;
138 N = SRPAlgorithm.N_768;
141 N = SRPAlgorithm.N_1024;
144 N = SRPAlgorithm.N_1280;
147 N = SRPAlgorithm.N_1536;
150 N = SRPAlgorithm.N_2048;
153 throw new IllegalArgumentException(
154 "unknown default shared modulus bit length");
160 else // generate new N and g
165 if ((l % 256) != 0 || l < 512 || l > 2048)
166 throw new IllegalArgumentException(
167 "invalid shared modulus bit length");
171 // are we using this generator on the server side, or the client side?
172 v = (BigInteger) attributes.get(USER_VERIFIER);
175 public KeyPair generate()
179 BigInteger[] params = generateParameters();
180 BigInteger q = params[0];
183 if (Configuration.DEBUG)
185 log.fine("q: " + q.toString(16));
186 log.fine("N: " + N.toString(16));
187 log.fine("g: " + g.toString(16));
190 return (v != null ? hostKeyPair() : userKeyPair());
193 private synchronized BigInteger[] generateParameters()
195 // N A large safe prime (N = 2q+1, where q is prime)
196 // g A generator modulo N
198 byte[] qBytes = new byte[l / 8];
203 nextRandomBytes(qBytes);
204 q = new BigInteger(1, qBytes);
205 q = q.setBit(0).setBit(l - 2).clearBit(l - 1);
207 while (! q.isProbablePrime(80));
208 p = q.multiply(TWO).add(ONE);
210 while (p.bitLength() != l || ! p.isProbablePrime(80));
211 // compute g. from FIPS-186, Appendix 4: e == 2
212 BigInteger p_minus_1 = p.subtract(ONE);
214 // Set h = any integer, where 1 < h < p - 1 and
215 // h differs from any value previously tried
216 for (BigInteger h = TWO; h.compareTo(p_minus_1) < 0; h = h.add(ONE))
218 // Set g = h**2 mod p
219 g = h.modPow(TWO, p);
220 // If g = 1, go to step 3
224 return new BigInteger[] { q, p, g };
227 private KeyPair hostKeyPair()
229 byte[] bBytes = new byte[(l + 7) / 8];
235 nextRandomBytes(bBytes);
236 b = new BigInteger(1, bBytes);
238 while (b.compareTo(ONE) <= 0 || b.compareTo(N) >= 0);
239 B = THREE.multiply(v).add(g.modPow(b, N)).mod(N);
241 while (B.compareTo(ZERO) == 0 || B.compareTo(N) >= 0);
242 KeyPair result = new KeyPair(new SRPPublicKey(new BigInteger[] { N, g, B }),
243 new SRPPrivateKey(new BigInteger[] { N, g, b, v }));
247 private KeyPair userKeyPair()
249 byte[] aBytes = new byte[(l + 7) / 8];
255 nextRandomBytes(aBytes);
256 a = new BigInteger(1, aBytes);
258 while (a.compareTo(ONE) <= 0 || a.compareTo(N) >= 0);
261 while (A.compareTo(ZERO) == 0 || A.compareTo(N) >= 0);
262 KeyPair result = new KeyPair(new SRPPublicKey(new BigInteger[] { N, g, A }),
263 new SRPPrivateKey(new BigInteger[] { N, g, a }));
267 private void nextRandomBytes(byte[] buffer)
270 rnd.nextBytes(buffer);
272 getDefaultPRNG().nextBytes(buffer);
275 private PRNG getDefaultPRNG()
278 prng = PRNG.getInstance();