Annotation of src/usr.bin/ssh/dh.c, Revision 1.16
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"
1.16 ! provos 26: RCSID("$OpenBSD: dh.c,v 1.15 2001/06/22 21:27:07 provos 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;
1.16 ! provos 106: char line[2048];
1.1 provos 107: int best, bestcount, which;
108: int linenum;
109: struct dhgroup dhg;
110:
1.15 provos 111: if ((f = fopen(_PATH_DH_MODULI, "r")) == NULL &&
112: (f = fopen(_PATH_DH_PRIMES, "r")) == NULL) {
113: log("WARNING: %s does not exist, using old modulus", _PATH_DH_MODULI);
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: }
1.16 ! provos 137: rewind(f);
1.1 provos 138:
139: if (bestcount == 0) {
1.16 ! provos 140: fclose(f);
1.9 provos 141: log("WARNING: no suitable primes in %s", _PATH_DH_PRIMES);
142: return (NULL);
1.1 provos 143: }
144:
145: linenum = 0;
146: which = arc4random() % bestcount;
147: while (fgets(line, sizeof(line), f)) {
148: if (!parse_prime(linenum, line, &dhg))
1.9 provos 149: continue;
1.13 markus 150: if ((dhg.size > max || dhg.size < min) ||
151: dhg.size != best ||
152: linenum++ != which) {
1.1 provos 153: BN_free(dhg.g);
154: BN_free(dhg.p);
155: continue;
156: }
157: break;
158: }
159: fclose(f);
1.13 markus 160: if (linenum != which+1)
161: fatal("WARNING: line %d disappeared in %s, giving up",
162: which, _PATH_DH_PRIMES);
1.1 provos 163:
164: return (dh_new_group(dhg.g, dhg.p));
1.11 markus 165: }
166:
167: /* diffie-hellman-group1-sha1 */
168:
169: int
170: dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
171: {
172: int i;
173: int n = BN_num_bits(dh_pub);
174: int bits_set = 0;
175:
176: if (dh_pub->neg) {
177: log("invalid public DH value: negativ");
178: return 0;
179: }
180: for (i = 0; i <= n; i++)
181: if (BN_is_bit_set(dh_pub, i))
182: bits_set++;
183: debug("bits set: %d/%d", bits_set, BN_num_bits(dh->p));
184:
185: /* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */
186: if (bits_set > 1 && (BN_cmp(dh_pub, dh->p) == -1))
187: return 1;
188: log("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p));
189: return 0;
190: }
191:
192: void
193: dh_gen_key(DH *dh, int need)
194: {
195: int i, bits_set = 0, tries = 0;
196:
197: if (dh->p == NULL)
198: fatal("dh_gen_key: dh->p == NULL");
199: if (2*need >= BN_num_bits(dh->p))
200: fatal("dh_gen_key: group too small: %d (2*need %d)",
201: BN_num_bits(dh->p), 2*need);
202: do {
203: if (dh->priv_key != NULL)
204: BN_free(dh->priv_key);
205: dh->priv_key = BN_new();
206: if (dh->priv_key == NULL)
207: fatal("dh_gen_key: BN_new failed");
208: /* generate a 2*need bits random private exponent */
209: if (!BN_rand(dh->priv_key, 2*need, 0, 0))
210: fatal("dh_gen_key: BN_rand failed");
211: if (DH_generate_key(dh) == 0)
212: fatal("DH_generate_key");
213: for (i = 0; i <= BN_num_bits(dh->priv_key); i++)
214: if (BN_is_bit_set(dh->priv_key, i))
215: bits_set++;
216: debug("dh_gen_key: priv key bits set: %d/%d",
217: bits_set, BN_num_bits(dh->priv_key));
218: if (tries++ > 10)
219: fatal("dh_gen_key: too many bad keys: giving up");
220: } while (!dh_pub_is_valid(dh, dh->pub_key));
221: }
222:
223: DH *
224: dh_new_group_asc(const char *gen, const char *modulus)
225: {
226: DH *dh;
227:
228: dh = DH_new();
229: if (dh == NULL)
230: fatal("DH_new");
231:
1.14 markus 232: if (BN_hex2bn(&dh->p, modulus) == 0)
1.11 markus 233: fatal("BN_hex2bn p");
1.14 markus 234: if (BN_hex2bn(&dh->g, gen) == 0)
1.11 markus 235: fatal("BN_hex2bn g");
236:
237: return (dh);
238: }
239:
240: /*
241: * This just returns the group, we still need to generate the exchange
242: * value.
243: */
244:
245: DH *
246: dh_new_group(BIGNUM *gen, BIGNUM *modulus)
247: {
248: DH *dh;
249:
250: dh = DH_new();
251: if (dh == NULL)
252: fatal("DH_new");
253: dh->p = modulus;
254: dh->g = gen;
255:
256: return (dh);
257: }
258:
259: DH *
260: dh_new_group1(void)
261: {
262: static char *gen = "2", *group1 =
263: "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
264: "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
265: "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
266: "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
267: "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
268: "FFFFFFFF" "FFFFFFFF";
269:
270: return (dh_new_group_asc(gen, group1));
1.12 markus 271: }
272:
273: /*
274: * Estimates the group order for a Diffie-Hellman group that has an
275: * attack complexity approximately the same as O(2**bits). Estimate
276: * with: O(exp(1.9223 * (ln q)^(1/3) (ln ln q)^(2/3)))
277: */
278:
279: int
280: dh_estimate(int bits)
281: {
282:
283: if (bits < 64)
284: return (512); /* O(2**63) */
285: if (bits < 128)
286: return (1024); /* O(2**86) */
287: if (bits < 192)
288: return (2048); /* O(2**116) */
289: return (4096); /* O(2**156) */
1.1 provos 290: }
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