2 Copyright 2001, 2002, 2003, 2006 Free Software Foundation, Inc.
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39 package gnu.java.security.key.dss;
41 import gnu.java.security.hash.Sha160;
42 import gnu.java.security.util.PRNG;
44 import java.math.BigInteger;
45 import java.security.SecureRandom;
48 * An implementation of the DSA parameters generation as described in FIPS-186.
52 * <a href="http://www.itl.nist.gov/fipspubs/fip186.htm">Digital Signature
53 * Standard (DSS)</a>, Federal Information Processing Standards Publication
54 * 186. National Institute of Standards and Technology.
58 public static final int DSA_PARAMS_SEED = 0;
60 public static final int DSA_PARAMS_COUNTER = 1;
62 public static final int DSA_PARAMS_Q = 2;
64 public static final int DSA_PARAMS_P = 3;
66 public static final int DSA_PARAMS_E = 4;
68 public static final int DSA_PARAMS_G = 5;
70 /** The BigInteger constant 2. */
71 private static final BigInteger TWO = BigInteger.valueOf(2L);
73 private static final BigInteger TWO_POW_160 = TWO.pow(160);
75 /** The SHA instance to use. */
76 private Sha160 sha = new Sha160();
78 /** The length of the modulus of DSS keys generated by this instance. */
81 /** The optional {@link SecureRandom} instance to use. */
82 private SecureRandom rnd = null;
84 /** Our default source of randomness. */
85 private PRNG prng = null;
87 public FIPS186(int L, SecureRandom rnd)
96 * This method generates the DSS <code>p</code>, <code>q</code>, and
97 * <code>g</code> parameters only when <code>L</code> (the modulus length)
98 * is not one of the following: <code>512</code>, <code>768</code> and
99 * <code>1024</code>. For those values of <code>L</code>, this
100 * implementation uses pre-computed values of <code>p</code>,
101 * <code>q</code>, and <code>g</code> given in the document <i>CryptoSpec</i>
102 * included in the security guide documentation of the standard JDK
105 * The DSS requires two primes , <code>p</code> and <code>q</code>,
106 * satisfying the following three conditions:
108 * <li><code>2<sup>159</sup> < q < 2<sup>160</sup></code></li>
109 * <li><code>2<sup>L-1</sup> < p < 2<sup>L</sup></code> for a
110 * specified <code>L</code>, where <code>L = 512 + 64j</code> for some
111 * <code>0 <= j <= 8</code></li>
112 * <li>q divides p - 1.</li>
114 * The algorithm used to find these primes is as described in FIPS-186,
115 * section 2.2: GENERATION OF PRIMES. This prime generation scheme starts by
116 * using the {@link Sha160} and a user supplied <i>SEED</i> to construct a
117 * prime, <code>q</code>, in the range 2<sup>159</sup> < q < 2<sup>160</sup>.
118 * Once this is accomplished, the same <i>SEED</i> value is used to construct
119 * an <code>X</code> in the range <code>2<sup>L-1
120 * </sup> < X < 2<sup>L</sup>. The prime, <code>p</code>, is then
121 * formed by rounding <code>X</code> to a number congruent to <code>1 mod
122 * 2q</code>. In this implementation we use the same <i>SEED</i> value given
123 * in FIPS-186, Appendix 5.
125 public BigInteger[] generateParameters()
128 BigInteger SEED, alpha, U, q, OFFSET, SEED_PLUS_OFFSET, W, X, p, c, g;
130 byte[] kb = new byte[20]; // to hold 160 bits of randomness
132 // Let L-1 = n*160 + b, where b and n are integers and 0 <= b < 160.
133 int b = (L - 1) % 160;
134 int n = (L - 1 - b) / 160;
135 BigInteger[] V = new BigInteger[n + 1];
136 algorithm: while (true)
140 // 1. Choose an arbitrary sequence of at least 160 bits and
143 SEED = new BigInteger(1, kb).setBit(159).setBit(0);
144 // Let g be the length of SEED in bits. here always 160
145 // 2. Compute: U = SHA[SEED] XOR SHA[(SEED+1) mod 2**g]
146 alpha = SEED.add(BigInteger.ONE).mod(TWO_POW_160);
149 a = SEED.toByteArray();
150 sha.update(a, 0, a.length);
152 u = alpha.toByteArray();
153 sha.update(u, 0, u.length);
156 for (int i = 0; i < a.length; i++)
159 U = new BigInteger(1, a);
160 // 3. Form q from U by setting the most significant bit (the
161 // 2**159 bit) and the least significant bit to 1. In terms of
162 // boolean operations, q = U OR 2**159 OR 1. Note that
163 // 2**159 < q < 2**160.
164 q = U.setBit(159).setBit(0);
165 // 4. Use a robust primality testing algorithm to test whether
166 // q is prime(1). A robust primality test is one where the
167 // probability of a non-prime number passing the test is at
169 // 5. If q is not prime, go to step 1.
170 if (q.isProbablePrime(80))
173 // 6. Let counter = 0 and offset = 2.
178 OFFSET = BigInteger.valueOf(offset & 0xFFFFFFFFL);
179 SEED_PLUS_OFFSET = SEED.add(OFFSET);
180 // 7. For k = 0,...,n let V[k] = SHA[(SEED + offset + k) mod 2**g].
183 for (int k = 0; k <= n; k++)
186 .add(BigInteger.valueOf(k & 0xFFFFFFFFL))
187 .mod(TWO_POW_160).toByteArray();
188 sha.update(a, 0, a.length);
189 V[k] = new BigInteger(1, sha.digest());
192 // 8. Let W be the integer:
193 // V[0]+V[1]*2**160+...+V[n-1]*2**((n-1)*160)+(V[n]mod2**b)*2**(n*160)
194 // and let : X = W + 2**(L-1).
195 // Note that 0 <= W < 2**(L-1) and hence 2**(L-1) <= X < 2**L.
197 for (int k = 1; k < n; k++)
198 W = W.add(V[k].multiply(TWO.pow(k * 160)));
200 W = W.add(V[n].mod(TWO.pow(b)).multiply(TWO.pow(n * 160)));
201 X = W.add(TWO.pow(L - 1));
202 // 9. Let c = X mod 2q and set p = X - (c - 1).
203 // Note that p is congruent to 1 mod 2q.
204 c = X.mod(TWO.multiply(q));
205 p = X.subtract(c.subtract(BigInteger.ONE));
206 // 10. If p < 2**(L-1), then go to step 13.
207 if (p.compareTo(TWO.pow(L - 1)) >= 0)
209 // 11. Perform a robust primality test on p.
210 // 12. If p passes the test performed in step 11, go to step 15.
211 if (p.isProbablePrime(80))
214 // 13. Let counter = counter + 1 and offset = offset + n + 1.
217 // 14. If counter >= 4096 go to step 1, otherwise go to step 7.
222 // compute g. from FIPS-186, Appendix 4:
223 // 1. Generate p and q as specified in Appendix 2.
224 // 2. Let e = (p - 1) / q
225 BigInteger e = p.subtract(BigInteger.ONE).divide(q);
227 BigInteger p_minus_1 = p.subtract(BigInteger.ONE);
229 // 3. Set h = any integer, where 1 < h < p - 1 and
230 // h differs from any value previously tried
231 for (; h.compareTo(p_minus_1) < 0; h = h.add(BigInteger.ONE))
233 // 4. Set g = h**e mod p
235 // 5. If g = 1, go to step 3
236 if (! g.equals(BigInteger.ONE))
239 return new BigInteger[] { SEED, BigInteger.valueOf(counter), q, p, e, g };
243 * Fills the designated byte array with random data.
245 * @param buffer the byte array to fill with random data.
247 private void nextRandomBytes(byte[] buffer)
250 rnd.nextBytes(buffer);
252 getDefaultPRNG().nextBytes(buffer);
255 private PRNG getDefaultPRNG()
258 prng = PRNG.getInstance();