1 /* $OpenBSD: dh_check.c,v 1.28 2023/07/24 16:25:02 tb Exp $ */
2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
3 * All rights reserved.
4 *
5 * This package is an SSL implementation written
6 * by Eric Young (eay@cryptsoft.com).
7 * The implementation was written so as to conform with Netscapes SSL.
8 *
9 * This library is free for commercial and non-commercial use as long as
10 * the following conditions are aheared to. The following conditions
11 * apply to all code found in this distribution, be it the RC4, RSA,
12 * lhash, DES, etc., code; not just the SSL code. The SSL documentation
13 * included with this distribution is covered by the same copyright terms
14 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
15 *
16 * Copyright remains Eric Young's, and as such any Copyright notices in
17 * the code are not to be removed.
18 * If this package is used in a product, Eric Young should be given attribution
19 * as the author of the parts of the library used.
20 * This can be in the form of a textual message at program startup or
21 * in documentation (online or textual) provided with the package.
22 *
23 * Redistribution and use in source and binary forms, with or without
24 * modification, are permitted provided that the following conditions
25 * are met:
26 * 1. Redistributions of source code must retain the copyright
27 * notice, this list of conditions and the following disclaimer.
28 * 2. Redistributions in binary form must reproduce the above copyright
29 * notice, this list of conditions and the following disclaimer in the
30 * documentation and/or other materials provided with the distribution.
31 * 3. All advertising materials mentioning features or use of this software
32 * must display the following acknowledgement:
33 * "This product includes cryptographic software written by
34 * Eric Young (eay@cryptsoft.com)"
35 * The word 'cryptographic' can be left out if the rouines from the library
36 * being used are not cryptographic related :-).
37 * 4. If you include any Windows specific code (or a derivative thereof) from
38 * the apps directory (application code) you must include an acknowledgement:
39 * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
40 *
41 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
42 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
43 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
44 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
45 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
46 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
47 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
48 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
49 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
50 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
51 * SUCH DAMAGE.
52 *
53 * The licence and distribution terms for any publically available version or
54 * derivative of this code cannot be changed. i.e. this code cannot simply be
55 * copied and put under another distribution licence
56 * [including the GNU Public Licence.]
57 */
58
59 #include <stdio.h>
60
61 #include <openssl/bn.h>
62 #include <openssl/dh.h>
63 #include <openssl/err.h>
64
65 #include "bn_local.h"
66 #include "dh_local.h"
67
68 #define DH_NUMBER_ITERATIONS_FOR_PRIME 64
69
70 /*
71 * Check that p is odd and 1 < g < p - 1. The _ex version removes the need of
72 * inspecting flags and pushes errors on the stack instead.
73 */
74
75 int
DH_check_params_ex(const DH * dh)76 DH_check_params_ex(const DH *dh)
77 {
78 int flags = 0;
79
80 if (!DH_check_params(dh, &flags))
81 return 0;
82
83 if ((flags & DH_CHECK_P_NOT_PRIME) != 0)
84 DHerror(DH_R_CHECK_P_NOT_PRIME);
85 if ((flags & DH_NOT_SUITABLE_GENERATOR) != 0)
86 DHerror(DH_R_NOT_SUITABLE_GENERATOR);
87
88 return flags == 0;
89 }
90
91 int
DH_check_params(const DH * dh,int * flags)92 DH_check_params(const DH *dh, int *flags)
93 {
94 BIGNUM *max_g = NULL;
95 int ok = 0;
96
97 *flags = 0;
98
99 if (!BN_is_odd(dh->p))
100 *flags |= DH_CHECK_P_NOT_PRIME;
101
102 /*
103 * Check that 1 < dh->g < p - 1
104 */
105
106 if (BN_cmp(dh->g, BN_value_one()) <= 0)
107 *flags |= DH_NOT_SUITABLE_GENERATOR;
108 /* max_g = p - 1 */
109 if ((max_g = BN_dup(dh->p)) == NULL)
110 goto err;
111 if (!BN_sub_word(max_g, 1))
112 goto err;
113 /* check that g < max_g */
114 if (BN_cmp(dh->g, max_g) >= 0)
115 *flags |= DH_NOT_SUITABLE_GENERATOR;
116
117 ok = 1;
118
119 err:
120 BN_free(max_g);
121
122 return ok;
123 }
124
125 /*
126 * Check that p is a safe prime and that g is a suitable generator.
127 * The _ex version puts errors on the stack instead of returning flags.
128 */
129
130 int
DH_check_ex(const DH * dh)131 DH_check_ex(const DH *dh)
132 {
133 int flags = 0;
134
135 if (!DH_check(dh, &flags))
136 return 0;
137
138 if ((flags & DH_NOT_SUITABLE_GENERATOR) != 0)
139 DHerror(DH_R_NOT_SUITABLE_GENERATOR);
140 if ((flags & DH_CHECK_Q_NOT_PRIME) != 0)
141 DHerror(DH_R_CHECK_Q_NOT_PRIME);
142 if ((flags & DH_CHECK_INVALID_Q_VALUE) != 0)
143 DHerror(DH_R_CHECK_INVALID_Q_VALUE);
144 if ((flags & DH_CHECK_INVALID_J_VALUE) != 0)
145 DHerror(DH_R_CHECK_INVALID_J_VALUE);
146 if ((flags & DH_UNABLE_TO_CHECK_GENERATOR) != 0)
147 DHerror(DH_R_UNABLE_TO_CHECK_GENERATOR);
148 if ((flags & DH_CHECK_P_NOT_PRIME) != 0)
149 DHerror(DH_R_CHECK_P_NOT_PRIME);
150 if ((flags & DH_CHECK_P_NOT_SAFE_PRIME) != 0)
151 DHerror(DH_R_CHECK_P_NOT_SAFE_PRIME);
152
153 return flags == 0;
154 }
155
156 int
DH_check(const DH * dh,int * flags)157 DH_check(const DH *dh, int *flags)
158 {
159 BN_CTX *ctx = NULL;
160 int is_prime;
161 int ok = 0;
162
163 *flags = 0;
164
165 if (!DH_check_params(dh, flags))
166 goto err;
167
168 ctx = BN_CTX_new();
169 if (ctx == NULL)
170 goto err;
171 BN_CTX_start(ctx);
172
173 if (dh->q != NULL) {
174 BIGNUM *quotient, *residue;
175
176 if ((quotient = BN_CTX_get(ctx)) == NULL)
177 goto err;
178 if ((residue = BN_CTX_get(ctx)) == NULL)
179 goto err;
180 if ((*flags & DH_NOT_SUITABLE_GENERATOR) == 0) {
181 /* Check g^q == 1 mod p */
182 if (!BN_mod_exp_ct(residue, dh->g, dh->q, dh->p, ctx))
183 goto err;
184 if (!BN_is_one(residue))
185 *flags |= DH_NOT_SUITABLE_GENERATOR;
186 }
187 is_prime = BN_is_prime_ex(dh->q, DH_NUMBER_ITERATIONS_FOR_PRIME,
188 ctx, NULL);
189 if (is_prime < 0)
190 goto err;
191 if (is_prime == 0)
192 *flags |= DH_CHECK_Q_NOT_PRIME;
193 /* Check p == 1 mod q, i.e., q divides p - 1 */
194 if (!BN_div_ct(quotient, residue, dh->p, dh->q, ctx))
195 goto err;
196 if (!BN_is_one(residue))
197 *flags |= DH_CHECK_INVALID_Q_VALUE;
198 if (dh->j != NULL && BN_cmp(dh->j, quotient) != 0)
199 *flags |= DH_CHECK_INVALID_J_VALUE;
200 }
201
202 is_prime = BN_is_prime_ex(dh->p, DH_NUMBER_ITERATIONS_FOR_PRIME,
203 ctx, NULL);
204 if (is_prime < 0)
205 goto err;
206 if (is_prime == 0)
207 *flags |= DH_CHECK_P_NOT_PRIME;
208 else if (dh->q == NULL) {
209 BIGNUM *q;
210
211 if ((q = BN_CTX_get(ctx)) == NULL)
212 goto err;
213 if (!BN_rshift1(q, dh->p))
214 goto err;
215 is_prime = BN_is_prime_ex(q, DH_NUMBER_ITERATIONS_FOR_PRIME,
216 ctx, NULL);
217 if (is_prime < 0)
218 goto err;
219 if (is_prime == 0)
220 *flags |= DH_CHECK_P_NOT_SAFE_PRIME;
221 }
222
223 ok = 1;
224
225 err:
226 BN_CTX_end(ctx);
227 BN_CTX_free(ctx);
228 return ok;
229 }
230 LCRYPTO_ALIAS(DH_check);
231
232 int
DH_check_pub_key_ex(const DH * dh,const BIGNUM * pub_key)233 DH_check_pub_key_ex(const DH *dh, const BIGNUM *pub_key)
234 {
235 int flags = 0;
236
237 if (!DH_check_pub_key(dh, pub_key, &flags))
238 return 0;
239
240 if ((flags & DH_CHECK_PUBKEY_TOO_SMALL) != 0)
241 DHerror(DH_R_CHECK_PUBKEY_TOO_SMALL);
242 if ((flags & DH_CHECK_PUBKEY_TOO_LARGE) != 0)
243 DHerror(DH_R_CHECK_PUBKEY_TOO_LARGE);
244 if ((flags & DH_CHECK_PUBKEY_INVALID) != 0)
245 DHerror(DH_R_CHECK_PUBKEY_INVALID);
246
247 return flags == 0;
248 }
249
250 int
DH_check_pub_key(const DH * dh,const BIGNUM * pub_key,int * flags)251 DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *flags)
252 {
253 BN_CTX *ctx = NULL;
254 BIGNUM *max_pub_key;
255 int ok = 0;
256
257 *flags = 0;
258
259 if ((ctx = BN_CTX_new()) == NULL)
260 goto err;
261 BN_CTX_start(ctx);
262 if ((max_pub_key = BN_CTX_get(ctx)) == NULL)
263 goto err;
264
265 /*
266 * Check that 1 < pub_key < dh->p - 1
267 */
268
269 if (BN_cmp(pub_key, BN_value_one()) <= 0)
270 *flags |= DH_CHECK_PUBKEY_TOO_SMALL;
271
272 /* max_pub_key = dh->p - 1 */
273 if (!BN_sub(max_pub_key, dh->p, BN_value_one()))
274 goto err;
275
276 if (BN_cmp(pub_key, max_pub_key) >= 0)
277 *flags |= DH_CHECK_PUBKEY_TOO_LARGE;
278
279 /*
280 * If dh->q is set, check that pub_key^q == 1 mod p
281 */
282
283 if (dh->q != NULL) {
284 BIGNUM *residue;
285
286 if ((residue = BN_CTX_get(ctx)) == NULL)
287 goto err;
288
289 if (!BN_mod_exp_ct(residue, pub_key, dh->q, dh->p, ctx))
290 goto err;
291 if (!BN_is_one(residue))
292 *flags |= DH_CHECK_PUBKEY_INVALID;
293 }
294
295 ok = 1;
296
297 err:
298 BN_CTX_end(ctx);
299 BN_CTX_free(ctx);
300
301 return ok;
302 }
303 LCRYPTO_ALIAS(DH_check_pub_key);
304