1/*
2 * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10#include <stdio.h>
11#include "internal/cryptlib.h"
12#include "dh_local.h"
13#include "crypto/bn.h"
14
15static int generate_key(DH *dh);
16static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
17static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
18 const BIGNUM *a, const BIGNUM *p,
19 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
20static int dh_init(DH *dh);
21static int dh_finish(DH *dh);
22
23int DH_generate_key(DH *dh)
24{
25 return dh->meth->generate_key(dh);
26}
27
28int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
29{
30 return dh->meth->compute_key(key, pub_key, dh);
31}
32
33int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
34{
35 int rv, pad;
36 rv = dh->meth->compute_key(key, pub_key, dh);
37 if (rv <= 0)
38 return rv;
39 pad = BN_num_bytes(dh->p) - rv;
40 if (pad > 0) {
41 memmove(key + pad, key, rv);
42 memset(key, 0, pad);
43 }
44 return rv + pad;
45}
46
47static DH_METHOD dh_ossl = {
48 "OpenSSL DH Method",
49 generate_key,
50 compute_key,
51 dh_bn_mod_exp,
52 dh_init,
53 dh_finish,
54 DH_FLAG_FIPS_METHOD,
55 NULL,
56 NULL
57};
58
59static const DH_METHOD *default_DH_method = &dh_ossl;
60
61const DH_METHOD *DH_OpenSSL(void)
62{
63 return &dh_ossl;
64}
65
66void DH_set_default_method(const DH_METHOD *meth)
67{
68 default_DH_method = meth;
69}
70
71const DH_METHOD *DH_get_default_method(void)
72{
73 return default_DH_method;
74}
75
76static int generate_key(DH *dh)
77{
78 int ok = 0;
79 int generate_new_key = 0;
80 unsigned l;
81 BN_CTX *ctx = NULL;
82 BN_MONT_CTX *mont = NULL;
83 BIGNUM *pub_key = NULL, *priv_key = NULL;
84
85 if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
86 DHerr(DH_F_GENERATE_KEY, DH_R_MODULUS_TOO_LARGE);
87 return 0;
88 }
89
90 if (BN_num_bits(dh->p) < DH_MIN_MODULUS_BITS) {
91 DHerr(DH_F_GENERATE_KEY, DH_R_MODULUS_TOO_SMALL);
92 return 0;
93 }
94
95 ctx = BN_CTX_new();
96 if (ctx == NULL)
97 goto err;
98
99 if (dh->priv_key == NULL) {
100 priv_key = BN_secure_new();
101 if (priv_key == NULL)
102 goto err;
103 generate_new_key = 1;
104 } else
105 priv_key = dh->priv_key;
106
107 if (dh->pub_key == NULL) {
108 pub_key = BN_new();
109 if (pub_key == NULL)
110 goto err;
111 } else
112 pub_key = dh->pub_key;
113
114 if (dh->flags & DH_FLAG_CACHE_MONT_P) {
115 mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
116 dh->lock, dh->p, ctx);
117 if (!mont)
118 goto err;
119 }
120
121 if (generate_new_key) {
122 if (dh->q) {
123 do {
124 if (!BN_priv_rand_range(priv_key, dh->q))
125 goto err;
126 }
127 while (BN_is_zero(priv_key) || BN_is_one(priv_key));
128 } else {
129 /* secret exponent length */
130 l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
131 if (!BN_priv_rand(priv_key, l, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY))
132 goto err;
133 /*
134 * We handle just one known case where g is a quadratic non-residue:
135 * for g = 2: p % 8 == 3
136 */
137 if (BN_is_word(dh->g, DH_GENERATOR_2) && !BN_is_bit_set(dh->p, 2)) {
138 /* clear bit 0, since it won't be a secret anyway */
139 if (!BN_clear_bit(priv_key, 0))
140 goto err;
141 }
142 }
143 }
144
145 {
146 BIGNUM *prk = BN_new();
147
148 if (prk == NULL)
149 goto err;
150 BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
151
152 if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) {
153 BN_clear_free(prk);
154 goto err;
155 }
156 /* We MUST free prk before any further use of priv_key */
157 BN_clear_free(prk);
158 }
159
160 dh->pub_key = pub_key;
161 dh->priv_key = priv_key;
162 dh->dirty_cnt++;
163 ok = 1;
164 err:
165 if (ok != 1)
166 DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);
167
168 if (pub_key != dh->pub_key)
169 BN_free(pub_key);
170 if (priv_key != dh->priv_key)
171 BN_free(priv_key);
172 BN_CTX_free(ctx);
173 return ok;
174}
175
176static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
177{
178 BN_CTX *ctx = NULL;
179 BN_MONT_CTX *mont = NULL;
180 BIGNUM *tmp;
181 int ret = -1;
182 int check_result;
183
184 if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
185 DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);
186 goto err;
187 }
188
189 if (BN_num_bits(dh->p) < DH_MIN_MODULUS_BITS) {
190 DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_SMALL);
191 return 0;
192 }
193
194 ctx = BN_CTX_new();
195 if (ctx == NULL)
196 goto err;
197 BN_CTX_start(ctx);
198 tmp = BN_CTX_get(ctx);
199 if (tmp == NULL)
200 goto err;
201
202 if (dh->priv_key == NULL) {
203 DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);
204 goto err;
205 }
206
207 if (dh->flags & DH_FLAG_CACHE_MONT_P) {
208 mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
209 dh->lock, dh->p, ctx);
210 BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
211 if (!mont)
212 goto err;
213 }
214
215 if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
216 DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);
217 goto err;
218 }
219
220 if (!dh->
221 meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {
222 DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);
223 goto err;
224 }
225
226 ret = BN_bn2bin(tmp, key);
227 err:
228 BN_CTX_end(ctx);
229 BN_CTX_free(ctx);
230 return ret;
231}
232
233static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
234 const BIGNUM *a, const BIGNUM *p,
235 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
236{
237 return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
238}
239
240static int dh_init(DH *dh)
241{
242 dh->flags |= DH_FLAG_CACHE_MONT_P;
243 return 1;
244}
245
246static int dh_finish(DH *dh)
247{
248 BN_MONT_CTX_free(dh->method_mont_p);
249 return 1;
250}
251
252int dh_buf2key(DH *dh, const unsigned char *buf, size_t len)
253{
254 int err_reason = DH_R_BN_ERROR;
255 BIGNUM *pubkey = NULL;
256 const BIGNUM *p;
257 size_t p_size;
258
259 if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL)
260 goto err;
261 DH_get0_pqg(dh, &p, NULL, NULL);
262 if (p == NULL || (p_size = BN_num_bytes(p)) == 0) {
263 err_reason = DH_R_NO_PARAMETERS_SET;
264 goto err;
265 }
266 /*
267 * As per Section 4.2.8.1 of RFC 8446 fail if DHE's
268 * public key is of size not equal to size of p
269 */
270 if (BN_is_zero(pubkey) || p_size != len) {
271 err_reason = DH_R_INVALID_PUBKEY;
272 goto err;
273 }
274 if (DH_set0_key(dh, pubkey, NULL) != 1)
275 goto err;
276 return 1;
277err:
278 DHerr(DH_F_DH_BUF2KEY, err_reason);
279 BN_free(pubkey);
280 return 0;
281}
282
283size_t dh_key2buf(const DH *dh, unsigned char **pbuf_out)
284{
285 const BIGNUM *pubkey;
286 unsigned char *pbuf;
287 const BIGNUM *p;
288 int p_size;
289
290 DH_get0_pqg(dh, &p, NULL, NULL);
291 DH_get0_key(dh, &pubkey, NULL);
292 if (p == NULL || pubkey == NULL
293 || (p_size = BN_num_bytes(p)) == 0
294 || BN_num_bytes(pubkey) == 0) {
295 DHerr(DH_F_DH_KEY2BUF, DH_R_INVALID_PUBKEY);
296 return 0;
297 }
298 if ((pbuf = OPENSSL_malloc(p_size)) == NULL) {
299 DHerr(DH_F_DH_KEY2BUF, ERR_R_MALLOC_FAILURE);
300 return 0;
301 }
302 /*
303 * As per Section 4.2.8.1 of RFC 8446 left pad public
304 * key with zeros to the size of p
305 */
306 if (BN_bn2binpad(pubkey, pbuf, p_size) < 0) {
307 OPENSSL_free(pbuf);
308 DHerr(DH_F_DH_KEY2BUF, DH_R_BN_ERROR);
309 return 0;
310 }
311 *pbuf_out = pbuf;
312 return p_size;
313}
314