1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
|
/*
* Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <stdio.h>
#include "internal/cryptlib.h"
#include "dh_local.h"
#include "crypto/bn.h"
static int generate_key(DH *dh);
static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
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);
static int dh_init(DH *dh);
static int dh_finish(DH *dh);
int DH_generate_key(DH *dh)
{
return dh->meth->generate_key(dh);
}
/*-
* NB: This function is inherently not constant time due to the
* RFC 5246 (8.1.2) padding style that strips leading zero bytes.
*/
int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
{
int ret = 0, i;
volatile size_t npad = 0, mask = 1;
/* compute the key; ret is constant unless compute_key is external */
if ((ret = dh->meth->compute_key(key, pub_key, dh)) <= 0)
return ret;
/* count leading zero bytes, yet still touch all bytes */
for (i = 0; i < ret; i++) {
mask &= !key[i];
npad += mask;
}
/* unpad key */
ret -= npad;
/* key-dependent memory access, potentially leaking npad / ret */
memmove(key, key + npad, ret);
/* key-dependent memory access, potentially leaking npad / ret */
memset(key + ret, 0, npad);
return ret;
}
int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
{
int rv, pad;
/* rv is constant unless compute_key is external */
rv = dh->meth->compute_key(key, pub_key, dh);
if (rv <= 0)
return rv;
pad = BN_num_bytes(dh->p) - rv;
/* pad is constant (zero) unless compute_key is external */
if (pad > 0) {
memmove(key + pad, key, rv);
memset(key, 0, pad);
}
return rv + pad;
}
static DH_METHOD dh_ossl = {
"OpenSSL DH Method",
generate_key,
compute_key,
dh_bn_mod_exp,
dh_init,
dh_finish,
DH_FLAG_FIPS_METHOD,
NULL,
NULL
};
static const DH_METHOD *default_DH_method = &dh_ossl;
const DH_METHOD *DH_OpenSSL(void)
{
return &dh_ossl;
}
void DH_set_default_method(const DH_METHOD *meth)
{
default_DH_method = meth;
}
const DH_METHOD *DH_get_default_method(void)
{
return default_DH_method;
}
static int generate_key(DH *dh)
{
int ok = 0;
int generate_new_key = 0;
unsigned l;
BN_CTX *ctx = NULL;
BN_MONT_CTX *mont = NULL;
BIGNUM *pub_key = NULL, *priv_key = NULL;
if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
DHerr(DH_F_GENERATE_KEY, DH_R_MODULUS_TOO_LARGE);
return 0;
}
ctx = BN_CTX_new();
if (ctx == NULL)
goto err;
if (dh->priv_key == NULL) {
priv_key = BN_secure_new();
if (priv_key == NULL)
goto err;
generate_new_key = 1;
} else
priv_key = dh->priv_key;
if (dh->pub_key == NULL) {
pub_key = BN_new();
if (pub_key == NULL)
goto err;
} else
pub_key = dh->pub_key;
if (dh->flags & DH_FLAG_CACHE_MONT_P) {
mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
dh->lock, dh->p, ctx);
if (!mont)
goto err;
}
if (generate_new_key) {
if (dh->q) {
do {
if (!BN_priv_rand_range(priv_key, dh->q))
goto err;
}
while (BN_is_zero(priv_key) || BN_is_one(priv_key));
} else {
/* secret exponent length */
l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
if (!BN_priv_rand(priv_key, l, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY))
goto err;
/*
* We handle just one known case where g is a quadratic non-residue:
* for g = 2: p % 8 == 3
*/
if (BN_is_word(dh->g, DH_GENERATOR_2) && !BN_is_bit_set(dh->p, 2)) {
/* clear bit 0, since it won't be a secret anyway */
if (!BN_clear_bit(priv_key, 0))
goto err;
}
}
}
{
BIGNUM *prk = BN_new();
if (prk == NULL)
goto err;
BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) {
BN_clear_free(prk);
goto err;
}
/* We MUST free prk before any further use of priv_key */
BN_clear_free(prk);
}
dh->pub_key = pub_key;
dh->priv_key = priv_key;
ok = 1;
err:
if (ok != 1)
DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);
if (pub_key != dh->pub_key)
BN_free(pub_key);
if (priv_key != dh->priv_key)
BN_free(priv_key);
BN_CTX_free(ctx);
return ok;
}
static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
{
BN_CTX *ctx = NULL;
BN_MONT_CTX *mont = NULL;
BIGNUM *tmp;
int ret = -1;
int check_result;
if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);
goto err;
}
ctx = BN_CTX_new();
if (ctx == NULL)
goto err;
BN_CTX_start(ctx);
tmp = BN_CTX_get(ctx);
if (tmp == NULL)
goto err;
if (dh->priv_key == NULL) {
DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);
goto err;
}
if (dh->flags & DH_FLAG_CACHE_MONT_P) {
mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
dh->lock, dh->p, ctx);
BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
if (!mont)
goto err;
}
if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);
goto err;
}
if (!dh->
meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {
DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);
goto err;
}
ret = BN_bn2binpad(tmp, key, BN_num_bytes(dh->p));
err:
BN_CTX_end(ctx);
BN_CTX_free(ctx);
return ret;
}
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)
{
return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
}
static int dh_init(DH *dh)
{
dh
|