1 /* $OpenBSD: dh_key.c,v 1.37 2022/01/07 09:27:13 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_lcl.h"
66 #include "dh_local.h"
67
68 static int generate_key(DH *dh);
69 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
70 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r, const BIGNUM *a,
71 const BIGNUM *p, const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
72 static int dh_init(DH *dh);
73 static int dh_finish(DH *dh);
74
75 int
DH_generate_key(DH * dh)76 DH_generate_key(DH *dh)
77 {
78 return dh->meth->generate_key(dh);
79 }
80
81 int
DH_compute_key(unsigned char * key,const BIGNUM * pub_key,DH * dh)82 DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
83 {
84 return dh->meth->compute_key(key, pub_key, dh);
85 }
86
87 static DH_METHOD dh_ossl = {
88 .name = "OpenSSL DH Method",
89 .generate_key = generate_key,
90 .compute_key = compute_key,
91 .bn_mod_exp = dh_bn_mod_exp,
92 .init = dh_init,
93 .finish = dh_finish,
94 };
95
96 const DH_METHOD *
DH_OpenSSL(void)97 DH_OpenSSL(void)
98 {
99 return &dh_ossl;
100 }
101
102 static int
generate_key(DH * dh)103 generate_key(DH *dh)
104 {
105 int ok = 0;
106 unsigned l;
107 BN_CTX *ctx;
108 BN_MONT_CTX *mont = NULL;
109 BIGNUM *pub_key = NULL, *priv_key = NULL, *two = NULL;
110
111 if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
112 DHerror(DH_R_MODULUS_TOO_LARGE);
113 return 0;
114 }
115
116 ctx = BN_CTX_new();
117 if (ctx == NULL)
118 goto err;
119
120 if ((priv_key = dh->priv_key) == NULL) {
121 if ((priv_key = BN_new()) == NULL)
122 goto err;
123 }
124
125 if ((pub_key = dh->pub_key) == NULL) {
126 if ((pub_key = BN_new()) == NULL)
127 goto err;
128 }
129
130 if (dh->flags & DH_FLAG_CACHE_MONT_P) {
131 mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
132 CRYPTO_LOCK_DH, dh->p, ctx);
133 if (!mont)
134 goto err;
135 }
136
137 if (dh->priv_key == NULL) {
138 if (dh->q) {
139 if ((two = BN_new()) == NULL)
140 goto err;
141 if (!BN_add(two, BN_value_one(), BN_value_one()))
142 goto err;
143 if (!bn_rand_interval(priv_key, two, dh->q))
144 goto err;
145 } else {
146 /* secret exponent length */
147 l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
148 if (!BN_rand(priv_key, l, 0, 0))
149 goto err;
150 }
151 }
152
153 if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, priv_key, dh->p, ctx,
154 mont))
155 goto err;
156
157 dh->pub_key = pub_key;
158 dh->priv_key = priv_key;
159 ok = 1;
160 err:
161 if (ok != 1)
162 DHerror(ERR_R_BN_LIB);
163
164 if (dh->pub_key == NULL)
165 BN_free(pub_key);
166 if (dh->priv_key == NULL)
167 BN_free(priv_key);
168 BN_CTX_free(ctx);
169 BN_free(two);
170 return ok;
171 }
172
173 static int
compute_key(unsigned char * key,const BIGNUM * pub_key,DH * dh)174 compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
175 {
176 BN_CTX *ctx = NULL;
177 BN_MONT_CTX *mont = NULL;
178 BIGNUM *tmp;
179 int ret = -1;
180 int check_result;
181
182 if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
183 DHerror(DH_R_MODULUS_TOO_LARGE);
184 goto err;
185 }
186
187 ctx = BN_CTX_new();
188 if (ctx == NULL)
189 goto err;
190 BN_CTX_start(ctx);
191 if ((tmp = BN_CTX_get(ctx)) == NULL)
192 goto err;
193
194 if (dh->priv_key == NULL) {
195 DHerror(DH_R_NO_PRIVATE_VALUE);
196 goto err;
197 }
198
199 if (dh->flags & DH_FLAG_CACHE_MONT_P) {
200 mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
201 CRYPTO_LOCK_DH, dh->p, ctx);
202
203 BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
204
205 if (!mont)
206 goto err;
207 }
208
209 if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
210 DHerror(DH_R_INVALID_PUBKEY);
211 goto err;
212 }
213
214 if (!dh->meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx,
215 mont)) {
216 DHerror(ERR_R_BN_LIB);
217 goto err;
218 }
219
220 ret = BN_bn2bin(tmp, key);
221 err:
222 if (ctx != NULL) {
223 BN_CTX_end(ctx);
224 BN_CTX_free(ctx);
225 }
226 return ret;
227 }
228
229 static int
dh_bn_mod_exp(const DH * dh,BIGNUM * r,const BIGNUM * a,const BIGNUM * p,const BIGNUM * m,BN_CTX * ctx,BN_MONT_CTX * m_ctx)230 dh_bn_mod_exp(const DH *dh, BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
231 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
232 {
233 return BN_mod_exp_mont_ct(r, a, p, m, ctx, m_ctx);
234 }
235
236 static int
dh_init(DH * dh)237 dh_init(DH *dh)
238 {
239 dh->flags |= DH_FLAG_CACHE_MONT_P;
240 return 1;
241 }
242
243 static int
dh_finish(DH * dh)244 dh_finish(DH *dh)
245 {
246 BN_MONT_CTX_free(dh->method_mont_p);
247 return 1;
248 }
249