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1 | /* | |
2 | * Copyright (c) 2000 Niels Provos. All rights reserved. | |
3 | * | |
4 | * Redistribution and use in source and binary forms, with or without | |
5 | * modification, are permitted provided that the following conditions | |
6 | * are met: | |
7 | * 1. Redistributions of source code must retain the above copyright | |
8 | * notice, this list of conditions and the following disclaimer. | |
9 | * 2. Redistributions in binary form must reproduce the above copyright | |
10 | * notice, this list of conditions and the following disclaimer in the | |
11 | * documentation and/or other materials provided with the distribution. | |
12 | * | |
13 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR | |
14 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
15 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
16 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
17 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
18 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
19 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
20 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
21 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
22 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
23 | */ | |
24 | ||
25 | #include "includes.h" | |
26 | RCSID("$OpenBSD: dh.c,v 1.14 2001/04/15 08:43:45 markus Exp $"); | |
27 | ||
28 | #include "xmalloc.h" | |
29 | ||
30 | #include <openssl/bn.h> | |
31 | #include <openssl/dh.h> | |
32 | #include <openssl/evp.h> | |
33 | ||
34 | #include "buffer.h" | |
35 | #include "cipher.h" | |
36 | #include "kex.h" | |
37 | #include "dh.h" | |
38 | #include "pathnames.h" | |
39 | #include "log.h" | |
40 | #include "misc.h" | |
41 | ||
42 | int | |
43 | parse_prime(int linenum, char *line, struct dhgroup *dhg) | |
44 | { | |
45 | char *cp, *arg; | |
46 | char *strsize, *gen, *prime; | |
47 | ||
48 | cp = line; | |
49 | arg = strdelim(&cp); | |
50 | /* Ignore leading whitespace */ | |
51 | if (*arg == '\0') | |
52 | arg = strdelim(&cp); | |
53 | if (!*arg || *arg == '#') | |
54 | return 0; | |
55 | ||
56 | /* time */ | |
57 | if (cp == NULL || *arg == '\0') | |
58 | goto fail; | |
59 | arg = strsep(&cp, " "); /* type */ | |
60 | if (cp == NULL || *arg == '\0') | |
61 | goto fail; | |
62 | arg = strsep(&cp, " "); /* tests */ | |
63 | if (cp == NULL || *arg == '\0') | |
64 | goto fail; | |
65 | arg = strsep(&cp, " "); /* tries */ | |
66 | if (cp == NULL || *arg == '\0') | |
67 | goto fail; | |
68 | strsize = strsep(&cp, " "); /* size */ | |
69 | if (cp == NULL || *strsize == '\0' || | |
70 | (dhg->size = atoi(strsize)) == 0) | |
71 | goto fail; | |
72 | /* The whole group is one bit larger */ | |
73 | dhg->size++; | |
74 | gen = strsep(&cp, " "); /* gen */ | |
75 | if (cp == NULL || *gen == '\0') | |
76 | goto fail; | |
77 | prime = strsep(&cp, " "); /* prime */ | |
78 | if (cp != NULL || *prime == '\0') | |
79 | goto fail; | |
80 | ||
81 | dhg->g = BN_new(); | |
82 | dhg->p = BN_new(); | |
83 | if (BN_hex2bn(&dhg->g, gen) == 0) | |
84 | goto failclean; | |
85 | ||
86 | if (BN_hex2bn(&dhg->p, prime) == 0) | |
87 | goto failclean; | |
88 | ||
89 | if (BN_num_bits(dhg->p) != dhg->size) | |
90 | goto failclean; | |
91 | ||
92 | return (1); | |
93 | ||
94 | failclean: | |
95 | BN_free(dhg->g); | |
96 | BN_free(dhg->p); | |
97 | fail: | |
98 | error("Bad prime description in line %d", linenum); | |
99 | return (0); | |
100 | } | |
101 | ||
102 | DH * | |
103 | choose_dh(int min, int wantbits, int max) | |
104 | { | |
105 | FILE *f; | |
106 | char line[1024]; | |
107 | int best, bestcount, which; | |
108 | int linenum; | |
109 | struct dhgroup dhg; | |
110 | ||
111 | f = fopen(_PATH_DH_PRIMES, "r"); | |
112 | if (!f) { | |
113 | log("WARNING: %s does not exist, using old prime", _PATH_DH_PRIMES); | |
114 | return (dh_new_group1()); | |
115 | } | |
116 | ||
117 | linenum = 0; | |
118 | best = bestcount = 0; | |
119 | while (fgets(line, sizeof(line), f)) { | |
120 | linenum++; | |
121 | if (!parse_prime(linenum, line, &dhg)) | |
122 | continue; | |
123 | BN_free(dhg.g); | |
124 | BN_free(dhg.p); | |
125 | ||
126 | if (dhg.size > max || dhg.size < min) | |
127 | continue; | |
128 | ||
129 | if ((dhg.size > wantbits && dhg.size < best) || | |
130 | (dhg.size > best && best < wantbits)) { | |
131 | best = dhg.size; | |
132 | bestcount = 0; | |
133 | } | |
134 | if (dhg.size == best) | |
135 | bestcount++; | |
136 | } | |
137 | fclose (f); | |
138 | ||
139 | if (bestcount == 0) { | |
140 | log("WARNING: no suitable primes in %s", _PATH_DH_PRIMES); | |
141 | return (NULL); | |
142 | } | |
143 | ||
144 | f = fopen(_PATH_DH_PRIMES, "r"); | |
145 | if (!f) { | |
146 | fatal("WARNING: %s disappeared, giving up", _PATH_DH_PRIMES); | |
147 | } | |
148 | ||
149 | linenum = 0; | |
150 | which = arc4random() % bestcount; | |
151 | while (fgets(line, sizeof(line), f)) { | |
152 | if (!parse_prime(linenum, line, &dhg)) | |
153 | continue; | |
154 | if ((dhg.size > max || dhg.size < min) || | |
155 | dhg.size != best || | |
156 | linenum++ != which) { | |
157 | BN_free(dhg.g); | |
158 | BN_free(dhg.p); | |
159 | continue; | |
160 | } | |
161 | break; | |
162 | } | |
163 | fclose(f); | |
164 | if (linenum != which+1) | |
165 | fatal("WARNING: line %d disappeared in %s, giving up", | |
166 | which, _PATH_DH_PRIMES); | |
167 | ||
168 | return (dh_new_group(dhg.g, dhg.p)); | |
169 | } | |
170 | ||
171 | /* diffie-hellman-group1-sha1 */ | |
172 | ||
173 | int | |
174 | dh_pub_is_valid(DH *dh, BIGNUM *dh_pub) | |
175 | { | |
176 | int i; | |
177 | int n = BN_num_bits(dh_pub); | |
178 | int bits_set = 0; | |
179 | ||
180 | if (dh_pub->neg) { | |
181 | log("invalid public DH value: negativ"); | |
182 | return 0; | |
183 | } | |
184 | for (i = 0; i <= n; i++) | |
185 | if (BN_is_bit_set(dh_pub, i)) | |
186 | bits_set++; | |
187 | debug("bits set: %d/%d", bits_set, BN_num_bits(dh->p)); | |
188 | ||
189 | /* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */ | |
190 | if (bits_set > 1 && (BN_cmp(dh_pub, dh->p) == -1)) | |
191 | return 1; | |
192 | log("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p)); | |
193 | return 0; | |
194 | } | |
195 | ||
196 | void | |
197 | dh_gen_key(DH *dh, int need) | |
198 | { | |
199 | int i, bits_set = 0, tries = 0; | |
200 | ||
201 | if (dh->p == NULL) | |
202 | fatal("dh_gen_key: dh->p == NULL"); | |
203 | if (2*need >= BN_num_bits(dh->p)) | |
204 | fatal("dh_gen_key: group too small: %d (2*need %d)", | |
205 | BN_num_bits(dh->p), 2*need); | |
206 | do { | |
207 | if (dh->priv_key != NULL) | |
208 | BN_free(dh->priv_key); | |
209 | dh->priv_key = BN_new(); | |
210 | if (dh->priv_key == NULL) | |
211 | fatal("dh_gen_key: BN_new failed"); | |
212 | /* generate a 2*need bits random private exponent */ | |
213 | if (!BN_rand(dh->priv_key, 2*need, 0, 0)) | |
214 | fatal("dh_gen_key: BN_rand failed"); | |
215 | if (DH_generate_key(dh) == 0) | |
216 | fatal("DH_generate_key"); | |
217 | for (i = 0; i <= BN_num_bits(dh->priv_key); i++) | |
218 | if (BN_is_bit_set(dh->priv_key, i)) | |
219 | bits_set++; | |
220 | debug("dh_gen_key: priv key bits set: %d/%d", | |
221 | bits_set, BN_num_bits(dh->priv_key)); | |
222 | if (tries++ > 10) | |
223 | fatal("dh_gen_key: too many bad keys: giving up"); | |
224 | } while (!dh_pub_is_valid(dh, dh->pub_key)); | |
225 | } | |
226 | ||
227 | DH * | |
228 | dh_new_group_asc(const char *gen, const char *modulus) | |
229 | { | |
230 | DH *dh; | |
231 | ||
232 | dh = DH_new(); | |
233 | if (dh == NULL) | |
234 | fatal("DH_new"); | |
235 | ||
236 | if (BN_hex2bn(&dh->p, modulus) == 0) | |
237 | fatal("BN_hex2bn p"); | |
238 | if (BN_hex2bn(&dh->g, gen) == 0) | |
239 | fatal("BN_hex2bn g"); | |
240 | ||
241 | return (dh); | |
242 | } | |
243 | ||
244 | /* | |
245 | * This just returns the group, we still need to generate the exchange | |
246 | * value. | |
247 | */ | |
248 | ||
249 | DH * | |
250 | dh_new_group(BIGNUM *gen, BIGNUM *modulus) | |
251 | { | |
252 | DH *dh; | |
253 | ||
254 | dh = DH_new(); | |
255 | if (dh == NULL) | |
256 | fatal("DH_new"); | |
257 | dh->p = modulus; | |
258 | dh->g = gen; | |
259 | ||
260 | return (dh); | |
261 | } | |
262 | ||
263 | DH * | |
264 | dh_new_group1(void) | |
265 | { | |
266 | static char *gen = "2", *group1 = | |
267 | "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1" | |
268 | "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD" | |
269 | "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245" | |
270 | "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED" | |
271 | "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381" | |
272 | "FFFFFFFF" "FFFFFFFF"; | |
273 | ||
274 | return (dh_new_group_asc(gen, group1)); | |
275 | } | |
276 | ||
277 | /* | |
278 | * Estimates the group order for a Diffie-Hellman group that has an | |
279 | * attack complexity approximately the same as O(2**bits). Estimate | |
280 | * with: O(exp(1.9223 * (ln q)^(1/3) (ln ln q)^(2/3))) | |
281 | */ | |
282 | ||
283 | int | |
284 | dh_estimate(int bits) | |
285 | { | |
286 | ||
287 | if (bits < 64) | |
288 | return (512); /* O(2**63) */ | |
289 | if (bits < 128) | |
290 | return (1024); /* O(2**86) */ | |
291 | if (bits < 192) | |
292 | return (2048); /* O(2**116) */ | |
293 | return (4096); /* O(2**156) */ | |
294 | } |