dh.c revision 162852
1/* $OpenBSD: dh.c,v 1.42 2006/08/03 03:34:42 deraadt 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 43static int 44parse_prime(int linenum, char *line, struct dhgroup *dhg) 45{ 46 char *cp, *arg; 47 char *strsize, *gen, *prime; 48 const char *errstr = NULL; 49 50 cp = line; 51 if ((arg = strdelim(&cp)) == NULL) 52 return 0; 53 /* Ignore leading whitespace */ 54 if (*arg == '\0') 55 arg = strdelim(&cp); 56 if (!arg || !*arg || *arg == '#') 57 return 0; 58 59 /* time */ 60 if (cp == NULL || *arg == '\0') 61 goto fail; 62 arg = strsep(&cp, " "); /* type */ 63 if (cp == NULL || *arg == '\0') 64 goto fail; 65 arg = strsep(&cp, " "); /* tests */ 66 if (cp == NULL || *arg == '\0') 67 goto fail; 68 arg = strsep(&cp, " "); /* tries */ 69 if (cp == NULL || *arg == '\0') 70 goto fail; 71 strsize = strsep(&cp, " "); /* size */ 72 if (cp == NULL || *strsize == '\0' || 73 (dhg->size = (u_int)strtonum(strsize, 0, 64*1024, &errstr)) == 0 || 74 errstr) 75 goto fail; 76 /* The whole group is one bit larger */ 77 dhg->size++; 78 gen = strsep(&cp, " "); /* gen */ 79 if (cp == NULL || *gen == '\0') 80 goto fail; 81 prime = strsep(&cp, " "); /* prime */ 82 if (cp != NULL || *prime == '\0') 83 goto fail; 84 85 if ((dhg->g = BN_new()) == NULL) 86 fatal("parse_prime: BN_new failed"); 87 if ((dhg->p = BN_new()) == NULL) 88 fatal("parse_prime: BN_new failed"); 89 if (BN_hex2bn(&dhg->g, gen) == 0) 90 goto failclean; 91 92 if (BN_hex2bn(&dhg->p, prime) == 0) 93 goto failclean; 94 95 if (BN_num_bits(dhg->p) != dhg->size) 96 goto failclean; 97 98 if (BN_is_zero(dhg->g) || BN_is_one(dhg->g)) 99 goto failclean; 100 101 return (1); 102 103 failclean: 104 BN_clear_free(dhg->g); 105 BN_clear_free(dhg->p); 106 fail: 107 error("Bad prime description in line %d", linenum); 108 return (0); 109} 110 111DH * 112choose_dh(int min, int wantbits, int max) 113{ 114 FILE *f; 115 char line[4096]; 116 int best, bestcount, which; 117 int linenum; 118 struct dhgroup dhg; 119 120 if ((f = fopen(_PATH_DH_MODULI, "r")) == NULL && 121 (f = fopen(_PATH_DH_PRIMES, "r")) == NULL) { 122 logit("WARNING: %s does not exist, using fixed modulus", 123 _PATH_DH_MODULI); 124 return (dh_new_group14()); 125 } 126 127 linenum = 0; 128 best = bestcount = 0; 129 while (fgets(line, sizeof(line), f)) { 130 linenum++; 131 if (!parse_prime(linenum, line, &dhg)) 132 continue; 133 BN_clear_free(dhg.g); 134 BN_clear_free(dhg.p); 135 136 if (dhg.size > max || dhg.size < min) 137 continue; 138 139 if ((dhg.size > wantbits && dhg.size < best) || 140 (dhg.size > best && best < wantbits)) { 141 best = dhg.size; 142 bestcount = 0; 143 } 144 if (dhg.size == best) 145 bestcount++; 146 } 147 rewind(f); 148 149 if (bestcount == 0) { 150 fclose(f); 151 logit("WARNING: no suitable primes in %s", _PATH_DH_PRIMES); 152 return (dh_new_group14()); 153 } 154 155 linenum = 0; 156 which = arc4random() % bestcount; 157 while (fgets(line, sizeof(line), f)) { 158 if (!parse_prime(linenum, line, &dhg)) 159 continue; 160 if ((dhg.size > max || dhg.size < min) || 161 dhg.size != best || 162 linenum++ != which) { 163 BN_clear_free(dhg.g); 164 BN_clear_free(dhg.p); 165 continue; 166 } 167 break; 168 } 169 fclose(f); 170 if (linenum != which+1) 171 fatal("WARNING: line %d disappeared in %s, giving up", 172 which, _PATH_DH_PRIMES); 173 174 return (dh_new_group(dhg.g, dhg.p)); 175} 176 177/* diffie-hellman-groupN-sha1 */ 178 179int 180dh_pub_is_valid(DH *dh, BIGNUM *dh_pub) 181{ 182 int i; 183 int n = BN_num_bits(dh_pub); 184 int bits_set = 0; 185 BIGNUM *tmp; 186 187 if (dh_pub->neg) { 188 logit("invalid public DH value: negativ"); 189 return 0; 190 } 191 if (BN_cmp(dh_pub, BN_value_one()) != 1) { /* pub_exp <= 1 */ 192 logit("invalid public DH value: <= 1"); 193 return 0; 194 } 195 196 if ((tmp = BN_new()) == NULL) 197 return (-1); 198 if (!BN_sub(tmp, dh->p, BN_value_one()) || 199 BN_cmp(dh_pub, tmp) != -1) { /* pub_exp > p-2 */ 200 BN_clear_free(tmp); 201 logit("invalid public DH value: >= p-1"); 202 return 0; 203 } 204 BN_clear_free(tmp); 205 206 for (i = 0; i <= n; i++) 207 if (BN_is_bit_set(dh_pub, i)) 208 bits_set++; 209 debug2("bits set: %d/%d", bits_set, BN_num_bits(dh->p)); 210 211 /* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */ 212 if (bits_set > 1) 213 return 1; 214 215 logit("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p)); 216 return 0; 217} 218 219void 220dh_gen_key(DH *dh, int need) 221{ 222 int i, bits_set, tries = 0; 223 224 if (dh->p == NULL) 225 fatal("dh_gen_key: dh->p == NULL"); 226 if (need > INT_MAX / 2 || 2 * need >= BN_num_bits(dh->p)) 227 fatal("dh_gen_key: group too small: %d (2*need %d)", 228 BN_num_bits(dh->p), 2*need); 229 do { 230 if (dh->priv_key != NULL) 231 BN_clear_free(dh->priv_key); 232 if ((dh->priv_key = BN_new()) == NULL) 233 fatal("dh_gen_key: BN_new failed"); 234 /* generate a 2*need bits random private exponent */ 235 if (!BN_rand(dh->priv_key, 2*need, 0, 0)) 236 fatal("dh_gen_key: BN_rand failed"); 237 if (DH_generate_key(dh) == 0) 238 fatal("DH_generate_key"); 239 for (i = 0, bits_set = 0; i <= BN_num_bits(dh->priv_key); i++) 240 if (BN_is_bit_set(dh->priv_key, i)) 241 bits_set++; 242 debug2("dh_gen_key: priv key bits set: %d/%d", 243 bits_set, BN_num_bits(dh->priv_key)); 244 if (tries++ > 10) 245 fatal("dh_gen_key: too many bad keys: giving up"); 246 } while (!dh_pub_is_valid(dh, dh->pub_key)); 247} 248 249DH * 250dh_new_group_asc(const char *gen, const char *modulus) 251{ 252 DH *dh; 253 254 if ((dh = DH_new()) == NULL) 255 fatal("dh_new_group_asc: DH_new"); 256 257 if (BN_hex2bn(&dh->p, modulus) == 0) 258 fatal("BN_hex2bn p"); 259 if (BN_hex2bn(&dh->g, gen) == 0) 260 fatal("BN_hex2bn g"); 261 262 return (dh); 263} 264 265/* 266 * This just returns the group, we still need to generate the exchange 267 * value. 268 */ 269 270DH * 271dh_new_group(BIGNUM *gen, BIGNUM *modulus) 272{ 273 DH *dh; 274 275 if ((dh = DH_new()) == NULL) 276 fatal("dh_new_group: DH_new"); 277 dh->p = modulus; 278 dh->g = gen; 279 280 return (dh); 281} 282 283DH * 284dh_new_group1(void) 285{ 286 static char *gen = "2", *group1 = 287 "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1" 288 "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD" 289 "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245" 290 "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED" 291 "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381" 292 "FFFFFFFF" "FFFFFFFF"; 293 294 return (dh_new_group_asc(gen, group1)); 295} 296 297DH * 298dh_new_group14(void) 299{ 300 static char *gen = "2", *group14 = 301 "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1" 302 "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD" 303 "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245" 304 "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED" 305 "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D" 306 "C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F" 307 "83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D" 308 "670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B" 309 "E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9" 310 "DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510" 311 "15728E5A" "8AACAA68" "FFFFFFFF" "FFFFFFFF"; 312 313 return (dh_new_group_asc(gen, group14)); 314} 315 316/* 317 * Estimates the group order for a Diffie-Hellman group that has an 318 * attack complexity approximately the same as O(2**bits). Estimate 319 * with: O(exp(1.9223 * (ln q)^(1/3) (ln ln q)^(2/3))) 320 */ 321 322int 323dh_estimate(int bits) 324{ 325 326 if (bits <= 128) 327 return (1024); /* O(2**86) */ 328 if (bits <= 192) 329 return (2048); /* O(2**116) */ 330 return (4096); /* O(2**156) */ 331} 332