1/* $OpenBSD: dh_key.c,v 1.42 2024/05/09 20:43:36 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
68static int
69generate_key(DH *dh)
70{
71	int ok = 0;
72	unsigned l;
73	BN_CTX *ctx;
74	BN_MONT_CTX *mont = NULL;
75	BIGNUM *pub_key = NULL, *priv_key = NULL;
76
77	if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
78		DHerror(DH_R_MODULUS_TOO_LARGE);
79		return 0;
80	}
81
82	ctx = BN_CTX_new();
83	if (ctx == NULL)
84		goto err;
85
86	if ((priv_key = dh->priv_key) == NULL) {
87		if ((priv_key = BN_new()) == NULL)
88			goto err;
89	}
90
91	if ((pub_key = dh->pub_key) == NULL) {
92		if ((pub_key = BN_new()) == NULL)
93			goto err;
94	}
95
96	if (dh->flags & DH_FLAG_CACHE_MONT_P) {
97		mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
98		    CRYPTO_LOCK_DH, dh->p, ctx);
99		if (!mont)
100			goto err;
101	}
102
103	if (dh->priv_key == NULL) {
104		if (dh->q) {
105			if (!bn_rand_interval(priv_key, 2, dh->q))
106				goto err;
107		} else {
108			/* secret exponent length */
109			l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
110			if (!BN_rand(priv_key, l, 0, 0))
111				goto err;
112		}
113	}
114
115	if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, priv_key, dh->p, ctx,
116	    mont))
117		goto err;
118
119	dh->pub_key = pub_key;
120	dh->priv_key = priv_key;
121	ok = 1;
122 err:
123	if (ok != 1)
124		DHerror(ERR_R_BN_LIB);
125
126	if (dh->pub_key == NULL)
127		BN_free(pub_key);
128	if (dh->priv_key == NULL)
129		BN_free(priv_key);
130	BN_CTX_free(ctx);
131
132	return ok;
133}
134
135static int
136compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
137{
138	BN_CTX *ctx = NULL;
139	BN_MONT_CTX *mont = NULL;
140	BIGNUM *tmp;
141	int ret = -1;
142        int check_result;
143
144	if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
145		DHerror(DH_R_MODULUS_TOO_LARGE);
146		goto err;
147	}
148
149	ctx = BN_CTX_new();
150	if (ctx == NULL)
151		goto err;
152	BN_CTX_start(ctx);
153	if ((tmp = BN_CTX_get(ctx)) == NULL)
154		goto err;
155
156	if (dh->priv_key == NULL) {
157		DHerror(DH_R_NO_PRIVATE_VALUE);
158		goto err;
159	}
160
161	if (dh->flags & DH_FLAG_CACHE_MONT_P) {
162		mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
163		    CRYPTO_LOCK_DH, dh->p, ctx);
164
165		BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
166
167		if (!mont)
168			goto err;
169	}
170
171        if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
172		DHerror(DH_R_INVALID_PUBKEY);
173		goto err;
174	}
175
176	if (!dh->meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx,
177	    mont)) {
178		DHerror(ERR_R_BN_LIB);
179		goto err;
180	}
181
182	ret = BN_bn2bin(tmp, key);
183 err:
184	if (ctx != NULL) {
185		BN_CTX_end(ctx);
186		BN_CTX_free(ctx);
187	}
188	return ret;
189}
190
191static int
192dh_bn_mod_exp(const DH *dh, BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
193    const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
194{
195	return BN_mod_exp_mont_ct(r, a, p, m, ctx, m_ctx);
196}
197
198static int
199dh_init(DH *dh)
200{
201	dh->flags |= DH_FLAG_CACHE_MONT_P;
202	return 1;
203}
204
205static int
206dh_finish(DH *dh)
207{
208	BN_MONT_CTX_free(dh->method_mont_p);
209	return 1;
210}
211
212int
213DH_generate_key(DH *dh)
214{
215	return dh->meth->generate_key(dh);
216}
217LCRYPTO_ALIAS(DH_generate_key);
218
219int
220DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
221{
222	return dh->meth->compute_key(key, pub_key, dh);
223}
224LCRYPTO_ALIAS(DH_compute_key);
225
226static const DH_METHOD dh_ossl = {
227	.name = "OpenSSL DH Method",
228	.generate_key = generate_key,
229	.compute_key = compute_key,
230	.bn_mod_exp = dh_bn_mod_exp,
231	.init = dh_init,
232	.finish = dh_finish,
233};
234
235const DH_METHOD *
236DH_OpenSSL(void)
237{
238	return &dh_ossl;
239}
240LCRYPTO_ALIAS(DH_OpenSSL);
241