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1 : : /*
2 : : * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
3 : : *
4 : : * Licensed under the Apache License, Version 2.0 (the "License").
5 : : * You may not use this file except in compliance with the License.
6 : : * A copy of the License is located at
7 : : *
8 : : * http://aws.amazon.com/apache2.0
9 : : *
10 : : * or in the "license" file accompanying this file. This file is distributed
11 : : * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
12 : : * express or implied. See the License for the specific language governing
13 : : * permissions and limitations under the License.
14 : : */
15 : :
16 : : #include "crypto/s2n_dhe.h"
17 : :
18 : : #include <openssl/bn.h>
19 : : #include <openssl/dh.h>
20 : : #include <openssl/evp.h>
21 : : #include <stdint.h>
22 : :
23 : : #include "crypto/s2n_openssl.h"
24 : : #include "error/s2n_errno.h"
25 : : #include "stuffer/s2n_stuffer.h"
26 : : #include "utils/s2n_blob.h"
27 : : #include "utils/s2n_mem.h"
28 : : #include "utils/s2n_safety.h"
29 : :
30 : : #define S2N_MIN_DH_PRIME_SIZE_BYTES (2048 / 8)
31 : :
32 : : /* Caller is not responsible for freeing values returned by these accessors
33 : : * Per https://www.openssl.org/docs/man1.1.0/crypto/DH_get0_pqg.html
34 : : */
35 : : static const BIGNUM *s2n_get_Ys_dh_param(struct s2n_dh_params *dh_params)
36 : 151 : {
37 : 151 : const BIGNUM *Ys = NULL;
38 : :
39 : : /* DH made opaque in Openssl 1.1.0 */
40 : 151 : #if S2N_OPENSSL_VERSION_AT_LEAST(1, 1, 0)
41 : 151 : DH_get0_key(dh_params->dh, &Ys, NULL);
42 : : #else
43 : : Ys = dh_params->dh->pub_key;
44 : : #endif
45 : :
46 : 151 : return Ys;
47 : 151 : }
48 : :
49 : : static const BIGNUM *s2n_get_p_dh_param(struct s2n_dh_params *dh_params)
50 : 362 : {
51 : 362 : const BIGNUM *p = NULL;
52 : 362 : #if S2N_OPENSSL_VERSION_AT_LEAST(1, 1, 0)
53 : 362 : DH_get0_pqg(dh_params->dh, &p, NULL, NULL);
54 : : #else
55 : : p = dh_params->dh->p;
56 : : #endif
57 : :
58 : 362 : return p;
59 : 362 : }
60 : :
61 : : static const BIGNUM *s2n_get_g_dh_param(struct s2n_dh_params *dh_params)
62 : 285 : {
63 : 285 : const BIGNUM *g = NULL;
64 : 285 : #if S2N_OPENSSL_VERSION_AT_LEAST(1, 1, 0)
65 : 285 : DH_get0_pqg(dh_params->dh, NULL, NULL, &g);
66 : : #else
67 : : g = dh_params->dh->g;
68 : : #endif
69 : :
70 : 285 : return g;
71 : 285 : }
72 : :
73 : : static int s2n_check_p_g_dh_params(struct s2n_dh_params *dh_params)
74 : 260 : {
75 [ - + ][ # # ]: 260 : POSIX_ENSURE_REF(dh_params);
76 [ - + ][ # # ]: 260 : POSIX_ENSURE_REF(dh_params->dh);
77 : :
78 : 260 : const BIGNUM *p = s2n_get_p_dh_param(dh_params);
79 : 260 : const BIGNUM *g = s2n_get_g_dh_param(dh_params);
80 : :
81 [ - + ][ # # ]: 260 : POSIX_ENSURE_REF(g);
82 [ # # ][ - + ]: 260 : POSIX_ENSURE_REF(p);
83 : :
84 [ - + ][ # # ]: 260 : S2N_ERROR_IF(DH_size(dh_params->dh) < S2N_MIN_DH_PRIME_SIZE_BYTES, S2N_ERR_DH_PARAMS_CREATE);
85 [ - + ][ # # ]: 260 : S2N_ERROR_IF(BN_is_zero(g), S2N_ERR_DH_PARAMS_CREATE);
86 [ - + ][ # # ]: 260 : S2N_ERROR_IF(BN_is_zero(p), S2N_ERR_DH_PARAMS_CREATE);
87 : :
88 : 260 : return S2N_SUCCESS;
89 : 260 : }
90 : :
91 : : static int s2n_check_pub_key_dh_params(struct s2n_dh_params *dh_params)
92 : 78 : {
93 : 78 : const BIGNUM *pub_key = s2n_get_Ys_dh_param(dh_params);
94 [ # # ][ - + ]: 78 : POSIX_ENSURE_REF(pub_key);
95 : :
96 : : /*
97 : : * https://www.rfc-editor.org/rfc/rfc2631#section-2.1.5
98 : : *
99 : : * The following algorithm MAY be used to validate a received public
100 : : * key y.
101 : : *
102 : : * 1. Verify that y lies within the interval [2,p-1].
103 : : * If it does not, the key is invalid.
104 : : *
105 : : * This check is optional per the RFC, but applied here as
106 : : * defense-in-depth to reject degenerate public key values.
107 : : */
108 [ - + ][ # # ]: 78 : S2N_ERROR_IF(BN_is_zero(pub_key), S2N_ERR_DH_PARAMS_CREATE);
109 [ + + ][ + - ]: 78 : S2N_ERROR_IF(BN_is_one(pub_key), S2N_ERR_DH_PARAMS_CREATE);
110 : :
111 : 77 : const BIGNUM *p = s2n_get_p_dh_param(dh_params);
112 [ # # ][ - + ]: 77 : POSIX_ENSURE_REF(p);
113 : :
114 : 77 : BIGNUM *p_minus_one = BN_dup(p);
115 [ - + ][ # # ]: 77 : POSIX_ENSURE_REF(p_minus_one);
116 [ - + ]: 77 : if (!BN_sub_word(p_minus_one, 1)) {
117 : 0 : BN_free(p_minus_one);
118 [ # # ]: 0 : POSIX_BAIL(S2N_ERR_DH_PARAMS_CREATE);
119 : 0 : }
120 : 77 : int cmp = BN_cmp(pub_key, p_minus_one);
121 : 77 : BN_free(p_minus_one);
122 [ + + ][ + - ]: 77 : S2N_ERROR_IF(cmp > 0, S2N_ERR_DH_PARAMS_CREATE);
123 : :
124 : 76 : return S2N_SUCCESS;
125 : 77 : }
126 : :
127 : : static int s2n_set_p_g_Ys_dh_params(struct s2n_dh_params *dh_params, struct s2n_blob *p, struct s2n_blob *g,
128 : : struct s2n_blob *Ys)
129 : 28 : {
130 [ - + ][ # # ]: 28 : POSIX_ENSURE(p->size <= INT_MAX, S2N_ERR_INTEGER_OVERFLOW);
131 [ - + ][ # # ]: 28 : POSIX_ENSURE(g->size <= INT_MAX, S2N_ERR_INTEGER_OVERFLOW);
132 [ # # ][ - + ]: 28 : POSIX_ENSURE(Ys->size <= INT_MAX, S2N_ERR_INTEGER_OVERFLOW);
133 : 28 : BIGNUM *bn_p = BN_bin2bn((const unsigned char *) p->data, p->size, NULL);
134 : 28 : BIGNUM *bn_g = BN_bin2bn((const unsigned char *) g->data, g->size, NULL);
135 : 28 : BIGNUM *bn_Ys = BN_bin2bn((const unsigned char *) Ys->data, Ys->size, NULL);
136 : :
137 : 28 : #if S2N_OPENSSL_VERSION_AT_LEAST(1, 1, 0)
138 : : /* Per https://www.openssl.org/docs/man1.1.0/crypto/DH_get0_pqg.html:
139 : : * values that have been passed in should not be freed directly after this function has been called
140 : : */
141 [ - + ][ # # ]: 28 : POSIX_GUARD_OSSL(DH_set0_pqg(dh_params->dh, bn_p, NULL, bn_g), S2N_ERR_DH_PARAMS_CREATE);
142 : :
143 : : /* Same as DH_set0_pqg */
144 [ - + ][ # # ]: 28 : POSIX_GUARD_OSSL(DH_set0_key(dh_params->dh, bn_Ys, NULL), S2N_ERR_DH_PARAMS_CREATE);
145 : : #else
146 : : dh_params->dh->p = bn_p;
147 : : dh_params->dh->g = bn_g;
148 : : dh_params->dh->pub_key = bn_Ys;
149 : : #endif
150 : :
151 : 28 : return S2N_SUCCESS;
152 : 28 : }
153 : :
154 : : int s2n_check_all_dh_params(struct s2n_dh_params *dh_params)
155 : 78 : {
156 [ - + ]: 78 : POSIX_GUARD(s2n_check_p_g_dh_params(dh_params));
157 [ + + ]: 78 : POSIX_GUARD(s2n_check_pub_key_dh_params(dh_params));
158 : :
159 : 76 : return S2N_SUCCESS;
160 : 78 : }
161 : :
162 : : int s2n_pkcs3_to_dh_params(struct s2n_dh_params *dh_params, struct s2n_blob *pkcs3)
163 : 84 : {
164 [ # # ][ - + ]: 84 : POSIX_ENSURE_REF(dh_params);
165 [ - + ][ + - ]: 84 : POSIX_PRECONDITION(s2n_blob_validate(pkcs3));
166 : 84 : DEFER_CLEANUP(struct s2n_dh_params temp_dh_params = { 0 }, s2n_dh_params_free);
167 : :
168 : 84 : uint8_t *original_ptr = pkcs3->data;
169 : 84 : temp_dh_params.dh = d2i_DHparams(NULL, (const unsigned char **) (void *) &pkcs3->data, pkcs3->size);
170 : :
171 [ - + ]: 84 : POSIX_GUARD(s2n_check_p_g_dh_params(&temp_dh_params));
172 : :
173 [ + - ]: 84 : if (pkcs3->data) {
174 [ - + ][ # # ]: 84 : POSIX_ENSURE_GTE(pkcs3->data, original_ptr);
175 [ - + ][ # # ]: 84 : POSIX_ENSURE((uint32_t) (pkcs3->data - original_ptr) == pkcs3->size, S2N_ERR_INVALID_PKCS3);
176 : 84 : }
177 : :
178 : 84 : pkcs3->data = original_ptr;
179 : :
180 : : /* Require at least 2048 bits for the DH size */
181 [ - + ][ # # ]: 84 : POSIX_ENSURE(DH_size(temp_dh_params.dh) >= S2N_MIN_DH_PRIME_SIZE_BYTES, S2N_ERR_DH_TOO_SMALL);
182 : :
183 : : /* Check the generator and prime */
184 [ - + ]: 84 : POSIX_GUARD(s2n_dh_params_check(&temp_dh_params));
185 : :
186 : 84 : dh_params->dh = temp_dh_params.dh;
187 : :
188 : 84 : ZERO_TO_DISABLE_DEFER_CLEANUP(temp_dh_params);
189 : :
190 : 84 : return S2N_SUCCESS;
191 : 84 : }
192 : :
193 : : int s2n_dh_p_g_Ys_to_dh_params(struct s2n_dh_params *server_dh_params, struct s2n_blob *p, struct s2n_blob *g,
194 : : struct s2n_blob *Ys)
195 : 28 : {
196 [ # # ][ - + ]: 28 : POSIX_ENSURE_REF(server_dh_params);
197 [ - + ][ + - ]: 28 : POSIX_PRECONDITION(s2n_blob_validate(p));
198 [ - + ][ + - ]: 28 : POSIX_PRECONDITION(s2n_blob_validate(g));
199 [ - + ][ + - ]: 28 : POSIX_PRECONDITION(s2n_blob_validate(Ys));
200 : :
201 : 28 : server_dh_params->dh = DH_new();
202 [ - + ][ # # ]: 28 : POSIX_ENSURE(server_dh_params->dh != NULL, S2N_ERR_DH_PARAMS_CREATE);
203 : :
204 [ - + ]: 28 : POSIX_GUARD(s2n_set_p_g_Ys_dh_params(server_dh_params, p, g, Ys));
205 [ + + ]: 28 : POSIX_GUARD(s2n_check_all_dh_params(server_dh_params));
206 : :
207 : 26 : return S2N_SUCCESS;
208 : 28 : }
209 : :
210 : : int s2n_dh_params_to_p_g_Ys(struct s2n_dh_params *server_dh_params, struct s2n_stuffer *out, struct s2n_blob *output)
211 : 25 : {
212 [ - + ]: 25 : POSIX_GUARD(s2n_check_all_dh_params(server_dh_params));
213 [ - + ][ + - ]: 25 : POSIX_PRECONDITION(s2n_stuffer_validate(out));
214 [ - + ][ + - ]: 25 : POSIX_PRECONDITION(s2n_blob_validate(output));
215 : :
216 : 25 : const BIGNUM *bn_p = s2n_get_p_dh_param(server_dh_params);
217 : 25 : const BIGNUM *bn_g = s2n_get_g_dh_param(server_dh_params);
218 : 25 : const BIGNUM *bn_Ys = s2n_get_Ys_dh_param(server_dh_params);
219 : :
220 : 25 : uint16_t p_size = BN_num_bytes(bn_p);
221 : 25 : uint16_t g_size = BN_num_bytes(bn_g);
222 : 25 : uint16_t Ys_size = BN_num_bytes(bn_Ys);
223 : 25 : uint8_t *p = NULL;
224 : 25 : uint8_t *g = NULL;
225 : 25 : uint8_t *Ys = NULL;
226 : :
227 : 25 : output->data = s2n_stuffer_raw_write(out, 0);
228 [ - + ][ # # ]: 25 : POSIX_ENSURE_REF(output->data);
229 : :
230 [ - + ]: 25 : POSIX_GUARD(s2n_stuffer_write_uint16(out, p_size));
231 : 25 : p = s2n_stuffer_raw_write(out, p_size);
232 [ - + ][ # # ]: 25 : POSIX_ENSURE_REF(p);
233 [ # # ][ - + ]: 25 : POSIX_ENSURE(BN_bn2bin(bn_p, p) == p_size, S2N_ERR_DH_SERIALIZING);
234 : :
235 [ - + ]: 25 : POSIX_GUARD(s2n_stuffer_write_uint16(out, g_size));
236 : 25 : g = s2n_stuffer_raw_write(out, g_size);
237 [ - + ][ # # ]: 25 : POSIX_ENSURE_REF(g);
238 [ # # ][ - + ]: 25 : POSIX_ENSURE(BN_bn2bin(bn_g, g) == g_size, S2N_ERR_DH_SERIALIZING);
239 : :
240 [ - + ]: 25 : POSIX_GUARD(s2n_stuffer_write_uint16(out, Ys_size));
241 : 25 : Ys = s2n_stuffer_raw_write(out, Ys_size);
242 [ - + ][ # # ]: 25 : POSIX_ENSURE_REF(Ys);
243 [ # # ][ - + ]: 25 : POSIX_ENSURE(BN_bn2bin(bn_Ys, Ys) == Ys_size, S2N_ERR_DH_SERIALIZING);
244 : :
245 : 25 : output->size = p_size + 2 + g_size + 2 + Ys_size + 2;
246 : :
247 : 25 : return S2N_SUCCESS;
248 : 25 : }
249 : :
250 : : int s2n_dh_compute_shared_secret_as_client(struct s2n_dh_params *server_dh_params, struct s2n_stuffer *Yc_out,
251 : : struct s2n_blob *shared_key)
252 : 24 : {
253 : 24 : struct s2n_dh_params client_params = { 0 };
254 : 24 : uint8_t *client_pub_key = NULL;
255 : 24 : uint16_t client_pub_key_size = 0;
256 : 24 : int shared_key_size = 0;
257 : :
258 [ - + ]: 24 : POSIX_GUARD(s2n_dh_params_check(server_dh_params));
259 [ - + ]: 24 : POSIX_GUARD(s2n_dh_params_copy(server_dh_params, &client_params));
260 [ - + ]: 24 : POSIX_GUARD(s2n_dh_generate_ephemeral_key(&client_params));
261 [ - + ]: 24 : POSIX_GUARD(s2n_alloc(shared_key, DH_size(server_dh_params->dh)));
262 : :
263 : 24 : const BIGNUM *client_pub_key_bn = s2n_get_Ys_dh_param(&client_params);
264 [ - + ][ # # ]: 24 : POSIX_ENSURE_REF(client_pub_key_bn);
265 : 24 : client_pub_key_size = BN_num_bytes(client_pub_key_bn);
266 [ - + ]: 24 : POSIX_GUARD(s2n_stuffer_write_uint16(Yc_out, client_pub_key_size));
267 : 24 : client_pub_key = s2n_stuffer_raw_write(Yc_out, client_pub_key_size);
268 [ - + ]: 24 : if (client_pub_key == NULL) {
269 [ # # ]: 0 : POSIX_GUARD(s2n_free(shared_key));
270 [ # # ]: 0 : POSIX_GUARD(s2n_dh_params_free(&client_params));
271 [ # # ]: 0 : POSIX_BAIL(S2N_ERR_DH_WRITING_PUBLIC_KEY);
272 : 0 : }
273 : :
274 [ - + ]: 24 : if (BN_bn2bin(client_pub_key_bn, client_pub_key) != client_pub_key_size) {
275 [ # # ]: 0 : POSIX_GUARD(s2n_free(shared_key));
276 [ # # ]: 0 : POSIX_GUARD(s2n_dh_params_free(&client_params));
277 [ # # ]: 0 : POSIX_BAIL(S2N_ERR_DH_COPYING_PUBLIC_KEY);
278 : 0 : }
279 : :
280 : : /* server_dh_params already validated */
281 : 24 : const BIGNUM *server_pub_key_bn = s2n_get_Ys_dh_param(server_dh_params);
282 : 24 : shared_key_size = DH_compute_key(shared_key->data, server_pub_key_bn, client_params.dh);
283 [ - + ]: 24 : if (shared_key_size < 0) {
284 [ # # ]: 0 : POSIX_GUARD(s2n_free(shared_key));
285 [ # # ]: 0 : POSIX_GUARD(s2n_dh_params_free(&client_params));
286 [ # # ]: 0 : POSIX_BAIL(S2N_ERR_DH_SHARED_SECRET);
287 : 0 : }
288 : :
289 : 24 : shared_key->size = shared_key_size;
290 : :
291 [ - + ]: 24 : POSIX_GUARD(s2n_dh_params_free(&client_params));
292 : :
293 : 24 : return S2N_SUCCESS;
294 : 24 : }
295 : :
296 : : int s2n_dh_compute_shared_secret_as_server(struct s2n_dh_params *server_dh_params, struct s2n_stuffer *Yc_in,
297 : : struct s2n_blob *shared_key)
298 : 25 : {
299 : 25 : uint16_t Yc_length = 0;
300 : 25 : struct s2n_blob Yc = { 0 };
301 : 25 : int shared_key_size = 0;
302 : 25 : BIGNUM *pub_key = NULL;
303 : :
304 [ - + ]: 25 : POSIX_GUARD(s2n_check_all_dh_params(server_dh_params));
305 : 25 : int server_dh_params_size = DH_size(server_dh_params->dh);
306 [ - + ][ # # ]: 25 : POSIX_ENSURE(server_dh_params_size <= INT32_MAX, S2N_ERR_INTEGER_OVERFLOW);
307 : :
308 : : /*
309 : : * As defined in https://www.rfc-editor.org/rfc/rfc5246#section-7.4.7.2,
310 : : * the client's DH public value (Yc) is sent as a variable-length opaque value.
311 : : * Validate that Yc_length does not exceed the DH group size to prevent
312 : : * unnecessary computation and memory allocation on oversized keys.
313 : : *
314 : : * According to https://www.rfc-editor.org/rfc/rfc2631#section-2.1.5,
315 : : * the valid range of Yc is [2, p-1]. When encoding a BIGNUM to bytes,
316 : : * leading zeros are often stripped, in which case Yc_length might be
317 : : * less than server_dh_params_size.
318 : : */
319 [ - + ]: 25 : POSIX_GUARD(s2n_stuffer_read_uint16(Yc_in, &Yc_length));
320 [ # # ][ - + ]: 25 : POSIX_ENSURE(Yc_length > 0, S2N_ERR_DH_SHARED_SECRET);
321 [ + + ][ + - ]: 25 : POSIX_ENSURE((int) Yc_length <= server_dh_params_size, S2N_ERR_DH_SHARED_SECRET);
322 : :
323 : 24 : Yc.size = Yc_length;
324 : 24 : Yc.data = s2n_stuffer_raw_read(Yc_in, Yc.size);
325 [ - + ][ # # ]: 24 : POSIX_ENSURE_REF(Yc.data);
326 : :
327 : 24 : pub_key = BN_bin2bn((const unsigned char *) Yc.data, Yc.size, NULL);
328 [ - + ][ # # ]: 24 : POSIX_ENSURE_REF(pub_key);
329 [ - + ]: 24 : POSIX_GUARD(s2n_alloc(shared_key, server_dh_params_size));
330 : :
331 : 24 : shared_key_size = DH_compute_key(shared_key->data, pub_key, server_dh_params->dh);
332 [ - + ]: 24 : if (shared_key_size <= 0) {
333 : 0 : BN_free(pub_key);
334 [ # # ]: 0 : POSIX_BAIL(S2N_ERR_DH_SHARED_SECRET);
335 : 0 : }
336 : :
337 : 24 : shared_key->size = shared_key_size;
338 : :
339 : 24 : BN_free(pub_key);
340 : :
341 : 24 : return S2N_SUCCESS;
342 : 24 : }
343 : :
344 : : int s2n_dh_params_check(struct s2n_dh_params *dh_params)
345 : 108 : {
346 [ # # ][ - + ]: 108 : POSIX_ENSURE_REF(dh_params);
347 [ - + ][ # # ]: 108 : POSIX_ENSURE_REF(dh_params->dh);
348 : 108 : int codes = 0;
349 : :
350 [ - + ][ # # ]: 108 : POSIX_GUARD_OSSL(DH_check(dh_params->dh, &codes), S2N_ERR_DH_PARAMETER_CHECK);
351 [ # # ][ - + ]: 108 : POSIX_ENSURE(codes == 0, S2N_ERR_DH_PARAMETER_CHECK);
352 : :
353 : 108 : return S2N_SUCCESS;
354 : 108 : }
355 : :
356 : : int s2n_dh_params_copy(struct s2n_dh_params *from, struct s2n_dh_params *to)
357 : 48 : {
358 [ - + ]: 48 : POSIX_GUARD(s2n_check_p_g_dh_params(from));
359 [ # # ][ - + ]: 48 : POSIX_ENSURE_REF(to);
360 : :
361 : 48 : to->dh = DHparams_dup(from->dh);
362 [ # # ][ - + ]: 48 : POSIX_ENSURE(to->dh != NULL, S2N_ERR_DH_COPYING_PARAMETERS);
363 : :
364 : 48 : return S2N_SUCCESS;
365 : 48 : }
366 : :
367 : : int s2n_dh_generate_ephemeral_key(struct s2n_dh_params *dh_params)
368 : 50 : {
369 [ - + ]: 50 : POSIX_GUARD(s2n_check_p_g_dh_params(dh_params));
370 : :
371 [ # # ][ - + ]: 50 : POSIX_GUARD_OSSL(DH_generate_key(dh_params->dh), S2N_ERR_DH_GENERATING_PARAMETERS);
372 : :
373 : 50 : return S2N_SUCCESS;
374 : 50 : }
375 : :
376 : : int s2n_dh_params_free(struct s2n_dh_params *dh_params)
377 : 3548927 : {
378 [ - + ][ # # ]: 3548927 : POSIX_ENSURE_REF(dh_params);
379 : 3548927 : DH_free(dh_params->dh);
380 : 3548927 : dh_params->dh = NULL;
381 : :
382 : 3548927 : return S2N_SUCCESS;
383 : 3548927 : }
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