1 /* $OpenBSD: dh.c,v 1.48 2009/10/01 11:37:33 grunk Exp $ */ 2 /* 3 * Copyright (c) 2000 Niels Provos. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 */ 25 26 #include "includes.h" 27 28 #include <sys/param.h> 29 30 #include <openssl/bn.h> 31 #include <openssl/dh.h> 32 33 #include <stdarg.h> 34 #include <stdio.h> 35 #include <stdlib.h> 36 #include <string.h> 37 38 #include "dh.h" 39 #include "pathnames.h" 40 #include "log.h" 41 #include "misc.h" 42 43 static int 44 parse_prime(int linenum, char *line, struct dhgroup *dhg) 45 { 46 char *cp, *arg; 47 char *strsize, *gen, *prime; 48 const char *errstr = NULL; 49 long long n; 50 51 cp = line; 52 if ((arg = strdelim(&cp)) == NULL) 53 return 0; 54 /* Ignore leading whitespace */ 55 if (*arg == '\0') 56 arg = strdelim(&cp); 57 if (!arg || !*arg || *arg == '#') 58 return 0; 59 60 /* time */ 61 if (cp == NULL || *arg == '\0') 62 goto fail; 63 arg = strsep(&cp, " "); /* type */ 64 if (cp == NULL || *arg == '\0') 65 goto fail; 66 /* Ensure this is a safe prime */ 67 n = strtonum(arg, 0, 5, &errstr); 68 if (errstr != NULL || n != MODULI_TYPE_SAFE) 69 goto fail; 70 arg = strsep(&cp, " "); /* tests */ 71 if (cp == NULL || *arg == '\0') 72 goto fail; 73 /* Ensure prime has been tested and is not composite */ 74 n = strtonum(arg, 0, 0x1f, &errstr); 75 if (errstr != NULL || 76 (n & MODULI_TESTS_COMPOSITE) || !(n & ~MODULI_TESTS_COMPOSITE)) 77 goto fail; 78 arg = strsep(&cp, " "); /* tries */ 79 if (cp == NULL || *arg == '\0') 80 goto fail; 81 n = strtonum(arg, 0, 1<<30, &errstr); 82 if (errstr != NULL || n == 0) 83 goto fail; 84 strsize = strsep(&cp, " "); /* size */ 85 if (cp == NULL || *strsize == '\0' || 86 (dhg->size = (int)strtonum(strsize, 0, 64*1024, &errstr)) == 0 || 87 errstr) 88 goto fail; 89 /* The whole group is one bit larger */ 90 dhg->size++; 91 gen = strsep(&cp, " "); /* gen */ 92 if (cp == NULL || *gen == '\0') 93 goto fail; 94 prime = strsep(&cp, " "); /* prime */ 95 if (cp != NULL || *prime == '\0') 96 goto fail; 97 98 if ((dhg->g = BN_new()) == NULL) 99 fatal("parse_prime: BN_new failed"); 100 if ((dhg->p = BN_new()) == NULL) 101 fatal("parse_prime: BN_new failed"); 102 if (BN_hex2bn(&dhg->g, gen) == 0) 103 goto failclean; 104 105 if (BN_hex2bn(&dhg->p, prime) == 0) 106 goto failclean; 107 108 if (BN_num_bits(dhg->p) != dhg->size) 109 goto failclean; 110 111 if (BN_is_zero(dhg->g) || BN_is_one(dhg->g)) 112 goto failclean; 113 114 return (1); 115 116 failclean: 117 BN_clear_free(dhg->g); 118 BN_clear_free(dhg->p); 119 fail: 120 error("Bad prime description in line %d", linenum); 121 return (0); 122 } 123 124 DH * 125 choose_dh(int min, int wantbits, int max) 126 { 127 FILE *f; 128 char line[4096]; 129 int best, bestcount, which; 130 int linenum; 131 struct dhgroup dhg; 132 133 if ((f = fopen(_PATH_DH_MODULI, "r")) == NULL && 134 (f = fopen(_PATH_DH_PRIMES, "r")) == NULL) { 135 logit("WARNING: %s does not exist, using fixed modulus", 136 _PATH_DH_MODULI); 137 return (dh_new_group14()); 138 } 139 140 linenum = 0; 141 best = bestcount = 0; 142 while (fgets(line, sizeof(line), f)) { 143 linenum++; 144 if (!parse_prime(linenum, line, &dhg)) 145 continue; 146 BN_clear_free(dhg.g); 147 BN_clear_free(dhg.p); 148 149 if (dhg.size > max || dhg.size < min) 150 continue; 151 152 if ((dhg.size > wantbits && dhg.size < best) || 153 (dhg.size > best && best < wantbits)) { 154 best = dhg.size; 155 bestcount = 0; 156 } 157 if (dhg.size == best) 158 bestcount++; 159 } 160 rewind(f); 161 162 if (bestcount == 0) { 163 fclose(f); 164 logit("WARNING: no suitable primes in %s", _PATH_DH_PRIMES); 165 return (dh_new_group14()); 166 } 167 168 linenum = 0; 169 which = arc4random_uniform(bestcount); 170 while (fgets(line, sizeof(line), f)) { 171 if (!parse_prime(linenum, line, &dhg)) 172 continue; 173 if ((dhg.size > max || dhg.size < min) || 174 dhg.size != best || 175 linenum++ != which) { 176 BN_clear_free(dhg.g); 177 BN_clear_free(dhg.p); 178 continue; 179 } 180 break; 181 } 182 fclose(f); 183 if (linenum != which+1) 184 fatal("WARNING: line %d disappeared in %s, giving up", 185 which, _PATH_DH_PRIMES); 186 187 return (dh_new_group(dhg.g, dhg.p)); 188 } 189 190 /* diffie-hellman-groupN-sha1 */ 191 192 int 193 dh_pub_is_valid(DH *dh, BIGNUM *dh_pub) 194 { 195 int i; 196 int n = BN_num_bits(dh_pub); 197 int bits_set = 0; 198 BIGNUM *tmp; 199 200 if (dh_pub->neg) { 201 logit("invalid public DH value: negative"); 202 return 0; 203 } 204 if (BN_cmp(dh_pub, BN_value_one()) != 1) { /* pub_exp <= 1 */ 205 logit("invalid public DH value: <= 1"); 206 return 0; 207 } 208 209 if ((tmp = BN_new()) == NULL) { 210 error("%s: BN_new failed", __func__); 211 return 0; 212 } 213 if (!BN_sub(tmp, dh->p, BN_value_one()) || 214 BN_cmp(dh_pub, tmp) != -1) { /* pub_exp > p-2 */ 215 BN_clear_free(tmp); 216 logit("invalid public DH value: >= p-1"); 217 return 0; 218 } 219 BN_clear_free(tmp); 220 221 for (i = 0; i <= n; i++) 222 if (BN_is_bit_set(dh_pub, i)) 223 bits_set++; 224 debug2("bits set: %d/%d", bits_set, BN_num_bits(dh->p)); 225 226 /* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */ 227 if (bits_set > 1) 228 return 1; 229 230 logit("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p)); 231 return 0; 232 } 233 234 void 235 dh_gen_key(DH *dh, int need) 236 { 237 int i, bits_set, tries = 0; 238 239 if (dh->p == NULL) 240 fatal("dh_gen_key: dh->p == NULL"); 241 if (need > INT_MAX / 2 || 2 * need >= BN_num_bits(dh->p)) 242 fatal("dh_gen_key: group too small: %d (2*need %d)", 243 BN_num_bits(dh->p), 2*need); 244 do { 245 if (dh->priv_key != NULL) 246 BN_clear_free(dh->priv_key); 247 if ((dh->priv_key = BN_new()) == NULL) 248 fatal("dh_gen_key: BN_new failed"); 249 /* generate a 2*need bits random private exponent */ 250 if (!BN_rand(dh->priv_key, 2*need, 0, 0)) 251 fatal("dh_gen_key: BN_rand failed"); 252 if (DH_generate_key(dh) == 0) 253 fatal("DH_generate_key"); 254 for (i = 0, bits_set = 0; i <= BN_num_bits(dh->priv_key); i++) 255 if (BN_is_bit_set(dh->priv_key, i)) 256 bits_set++; 257 debug2("dh_gen_key: priv key bits set: %d/%d", 258 bits_set, BN_num_bits(dh->priv_key)); 259 if (tries++ > 10) 260 fatal("dh_gen_key: too many bad keys: giving up"); 261 } while (!dh_pub_is_valid(dh, dh->pub_key)); 262 } 263 264 DH * 265 dh_new_group_asc(const char *gen, const char *modulus) 266 { 267 DH *dh; 268 269 if ((dh = DH_new()) == NULL) 270 fatal("dh_new_group_asc: DH_new"); 271 272 if (BN_hex2bn(&dh->p, modulus) == 0) 273 fatal("BN_hex2bn p"); 274 if (BN_hex2bn(&dh->g, gen) == 0) 275 fatal("BN_hex2bn g"); 276 277 return (dh); 278 } 279 280 /* 281 * This just returns the group, we still need to generate the exchange 282 * value. 283 */ 284 285 DH * 286 dh_new_group(BIGNUM *gen, BIGNUM *modulus) 287 { 288 DH *dh; 289 290 if ((dh = DH_new()) == NULL) 291 fatal("dh_new_group: DH_new"); 292 dh->p = modulus; 293 dh->g = gen; 294 295 return (dh); 296 } 297 298 DH * 299 dh_new_group1(void) 300 { 301 static char *gen = "2", *group1 = 302 "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1" 303 "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD" 304 "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245" 305 "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED" 306 "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381" 307 "FFFFFFFF" "FFFFFFFF"; 308 309 return (dh_new_group_asc(gen, group1)); 310 } 311 312 DH * 313 dh_new_group14(void) 314 { 315 static char *gen = "2", *group14 = 316 "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1" 317 "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD" 318 "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245" 319 "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED" 320 "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D" 321 "C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F" 322 "83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D" 323 "670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B" 324 "E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9" 325 "DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510" 326 "15728E5A" "8AACAA68" "FFFFFFFF" "FFFFFFFF"; 327 328 return (dh_new_group_asc(gen, group14)); 329 } 330 331 /* 332 * Estimates the group order for a Diffie-Hellman group that has an 333 * attack complexity approximately the same as O(2**bits). Estimate 334 * with: O(exp(1.9223 * (ln q)^(1/3) (ln ln q)^(2/3))) 335 */ 336 337 int 338 dh_estimate(int bits) 339 { 340 341 if (bits <= 128) 342 return (1024); /* O(2**86) */ 343 if (bits <= 192) 344 return (2048); /* O(2**116) */ 345 return (4096); /* O(2**156) */ 346 } 347