Annotation of src/usr.bin/ssh/dh.c, Revision 1.14
1.1 provos 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"
1.14 ! markus 26: RCSID("$OpenBSD: dh.c,v 1.13 2001/04/04 23:09:17 markus Exp $");
1.1 provos 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"
1.6 markus 35: #include "cipher.h"
1.1 provos 36: #include "kex.h"
37: #include "dh.h"
1.5 markus 38: #include "pathnames.h"
1.6 markus 39: #include "log.h"
40: #include "misc.h"
1.1 provos 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;
1.9 provos 72: /* The whole group is one bit larger */
73: dhg->size++;
1.1 provos 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();
1.14 ! markus 83: if (BN_hex2bn(&dhg->g, gen) == 0)
1.10 provos 84: goto failclean;
85:
1.14 ! markus 86: if (BN_hex2bn(&dhg->p, prime) == 0)
1.10 provos 87: goto failclean;
88:
89: if (BN_num_bits(dhg->p) != dhg->size)
90: goto failclean;
1.1 provos 91:
92: return (1);
1.10 provos 93:
94: failclean:
95: BN_free(dhg->g);
96: BN_free(dhg->p);
1.1 provos 97: fail:
1.7 millert 98: error("Bad prime description in line %d", linenum);
1.1 provos 99: return (0);
100: }
101:
102: DH *
1.9 provos 103: choose_dh(int min, int wantbits, int max)
1.1 provos 104: {
105: FILE *f;
106: char line[1024];
107: int best, bestcount, which;
108: int linenum;
109: struct dhgroup dhg;
110:
1.5 markus 111: f = fopen(_PATH_DH_PRIMES, "r");
1.1 provos 112: if (!f) {
1.5 markus 113: log("WARNING: %s does not exist, using old prime", _PATH_DH_PRIMES);
1.1 provos 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:
1.9 provos 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)) {
1.1 provos 131: best = dhg.size;
132: bestcount = 0;
133: }
134: if (dhg.size == best)
135: bestcount++;
136: }
137: fclose (f);
138:
139: if (bestcount == 0) {
1.9 provos 140: log("WARNING: no suitable primes in %s", _PATH_DH_PRIMES);
141: return (NULL);
1.1 provos 142: }
143:
1.5 markus 144: f = fopen(_PATH_DH_PRIMES, "r");
1.1 provos 145: if (!f) {
1.8 stevesk 146: fatal("WARNING: %s disappeared, giving up", _PATH_DH_PRIMES);
1.1 provos 147: }
148:
149: linenum = 0;
150: which = arc4random() % bestcount;
151: while (fgets(line, sizeof(line), f)) {
152: if (!parse_prime(linenum, line, &dhg))
1.9 provos 153: continue;
1.13 markus 154: if ((dhg.size > max || dhg.size < min) ||
155: dhg.size != best ||
156: linenum++ != which) {
1.1 provos 157: BN_free(dhg.g);
158: BN_free(dhg.p);
159: continue;
160: }
161: break;
162: }
163: fclose(f);
1.13 markus 164: if (linenum != which+1)
165: fatal("WARNING: line %d disappeared in %s, giving up",
166: which, _PATH_DH_PRIMES);
1.1 provos 167:
168: return (dh_new_group(dhg.g, dhg.p));
1.11 markus 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:
1.14 ! markus 236: if (BN_hex2bn(&dh->p, modulus) == 0)
1.11 markus 237: fatal("BN_hex2bn p");
1.14 ! markus 238: if (BN_hex2bn(&dh->g, gen) == 0)
1.11 markus 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));
1.12 markus 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) */
1.1 provos 294: }
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