1 /* FIPS186.java -- 2 Copyright 2001, 2002, 2003, 2006 Free Software Foundation, Inc. 3 4 This file is a part of GNU Classpath. 5 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. 10 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. 15 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 19 USA 20 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 24 combination. 25 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. */ 37 38 39 package gnu.java.security.key.dss; 40 41 import gnu.java.security.hash.Sha160; 42 import gnu.java.security.util.PRNG; 43 44 import java.math.BigInteger; 45 import java.security.SecureRandom; 46 47 /** 48 * An implementation of the DSA parameters generation as described in FIPS-186. 49 * <p> 50 * References: 51 * <p> 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. 55 */ 56 public class FIPS186 57 { 58 public static final int DSA_PARAMS_SEED = 0; 59 60 public static final int DSA_PARAMS_COUNTER = 1; 61 62 public static final int DSA_PARAMS_Q = 2; 63 64 public static final int DSA_PARAMS_P = 3; 65 66 public static final int DSA_PARAMS_E = 4; 67 68 public static final int DSA_PARAMS_G = 5; 69 70 /** The BigInteger constant 2. */ 71 private static final BigInteger TWO = BigInteger.valueOf(2L); 72 73 private static final BigInteger TWO_POW_160 = TWO.pow(160); 74 75 /** The SHA instance to use. */ 76 private Sha160 sha = new Sha160(); 77 78 /** The length of the modulus of DSS keys generated by this instance. */ 79 private int L; 80 81 /** The optional {@link SecureRandom} instance to use. */ 82 private SecureRandom rnd = null; 83 84 /** Our default source of randomness. */ 85 private PRNG prng = null; 86 FIPS186(int L, SecureRandom rnd)87 public FIPS186(int L, SecureRandom rnd) 88 { 89 super(); 90 91 this.L = L; 92 this.rnd = rnd; 93 } 94 95 /** 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 103 * distribution. 104 * <p> 105 * The DSS requires two primes , <code>p</code> and <code>q</code>, 106 * satisfying the following three conditions: 107 * <ul> 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> 113 * </ul> 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. 124 */ generateParameters()125 public BigInteger[] generateParameters() 126 { 127 int counter, offset; 128 BigInteger SEED, alpha, U, q, OFFSET, SEED_PLUS_OFFSET, W, X, p, c, g; 129 byte[] a, u; 130 byte[] kb = new byte[20]; // to hold 160 bits of randomness 131 132 // 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) 137 { 138 step1: while (true) 139 { 140 // 1. Choose an arbitrary sequence of at least 160 bits and 141 // call it SEED. 142 nextRandomBytes(kb); 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); 147 synchronized (sha) 148 { 149 a = SEED.toByteArray(); 150 sha.update(a, 0, a.length); 151 a = sha.digest(); 152 u = alpha.toByteArray(); 153 sha.update(u, 0, u.length); 154 u = sha.digest(); 155 } 156 for (int i = 0; i < a.length; i++) 157 a[i] ^= u[i]; 158 159 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 168 // most 1/2**80. 169 // 5. If q is not prime, go to step 1. 170 if (q.isProbablePrime(80)) 171 break step1; 172 } // step1 173 // 6. Let counter = 0 and offset = 2. 174 counter = 0; 175 offset = 2; 176 while (true) 177 { 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]. 181 synchronized (sha) 182 { 183 for (int k = 0; k <= n; k++) 184 { 185 a = SEED_PLUS_OFFSET 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()); 190 } 191 } 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. 196 W = V[0]; 197 for (int k = 1; k < n; k++) 198 W = W.add(V[k].multiply(TWO.pow(k * 160))); 199 200 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) 208 { 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)) 212 break algorithm; 213 } 214 // 13. Let counter = counter + 1 and offset = offset + n + 1. 215 counter++; 216 offset += n + 1; 217 // 14. If counter >= 4096 go to step 1, otherwise go to step 7. 218 if (counter >= 4096) 219 continue algorithm; 220 } // step7 221 } // algorithm 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); 226 BigInteger h = TWO; 227 BigInteger p_minus_1 = p.subtract(BigInteger.ONE); 228 g = TWO; 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)) 232 { 233 // 4. Set g = h**e mod p 234 g = h.modPow(e, p); 235 // 5. If g = 1, go to step 3 236 if (! g.equals(BigInteger.ONE)) 237 break; 238 } 239 return new BigInteger[] { SEED, BigInteger.valueOf(counter), q, p, e, g }; 240 } 241 242 /** 243 * Fills the designated byte array with random data. 244 * 245 * @param buffer the byte array to fill with random data. 246 */ nextRandomBytes(byte[] buffer)247 private void nextRandomBytes(byte[] buffer) 248 { 249 if (rnd != null) 250 rnd.nextBytes(buffer); 251 else 252 getDefaultPRNG().nextBytes(buffer); 253 } 254 getDefaultPRNG()255 private PRNG getDefaultPRNG() 256 { 257 if (prng == null) 258 prng = PRNG.getInstance(); 259 260 return prng; 261 } 262 } 263