1 /* $OpenBSD: tls12_key_schedule.c,v 1.4 2024/02/03 15:58:34 beck Exp $ */
2 /*
3 * Copyright (c) 2021 Joel Sing <jsing@openbsd.org>
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17
18 #include <stdlib.h>
19
20 #include <openssl/evp.h>
21
22 #include "bytestring.h"
23 #include "ssl_local.h"
24 #include "tls12_internal.h"
25
26 struct tls12_key_block {
27 CBS client_write_mac_key;
28 CBS server_write_mac_key;
29 CBS client_write_key;
30 CBS server_write_key;
31 CBS client_write_iv;
32 CBS server_write_iv;
33
34 uint8_t *key_block;
35 size_t key_block_len;
36 };
37
38 struct tls12_key_block *
tls12_key_block_new(void)39 tls12_key_block_new(void)
40 {
41 return calloc(1, sizeof(struct tls12_key_block));
42 }
43
44 static void
tls12_key_block_clear(struct tls12_key_block * kb)45 tls12_key_block_clear(struct tls12_key_block *kb)
46 {
47 CBS_init(&kb->client_write_mac_key, NULL, 0);
48 CBS_init(&kb->server_write_mac_key, NULL, 0);
49 CBS_init(&kb->client_write_key, NULL, 0);
50 CBS_init(&kb->server_write_key, NULL, 0);
51 CBS_init(&kb->client_write_iv, NULL, 0);
52 CBS_init(&kb->server_write_iv, NULL, 0);
53
54 freezero(kb->key_block, kb->key_block_len);
55 kb->key_block = NULL;
56 kb->key_block_len = 0;
57 }
58
59 void
tls12_key_block_free(struct tls12_key_block * kb)60 tls12_key_block_free(struct tls12_key_block *kb)
61 {
62 if (kb == NULL)
63 return;
64
65 tls12_key_block_clear(kb);
66
67 freezero(kb, sizeof(struct tls12_key_block));
68 }
69
70 void
tls12_key_block_client_write(struct tls12_key_block * kb,CBS * mac_key,CBS * key,CBS * iv)71 tls12_key_block_client_write(struct tls12_key_block *kb, CBS *mac_key,
72 CBS *key, CBS *iv)
73 {
74 CBS_dup(&kb->client_write_mac_key, mac_key);
75 CBS_dup(&kb->client_write_key, key);
76 CBS_dup(&kb->client_write_iv, iv);
77 }
78
79 void
tls12_key_block_server_write(struct tls12_key_block * kb,CBS * mac_key,CBS * key,CBS * iv)80 tls12_key_block_server_write(struct tls12_key_block *kb, CBS *mac_key,
81 CBS *key, CBS *iv)
82 {
83 CBS_dup(&kb->server_write_mac_key, mac_key);
84 CBS_dup(&kb->server_write_key, key);
85 CBS_dup(&kb->server_write_iv, iv);
86 }
87
88 int
tls12_key_block_generate(struct tls12_key_block * kb,SSL * s,const EVP_AEAD * aead,const EVP_CIPHER * cipher,const EVP_MD * mac_hash)89 tls12_key_block_generate(struct tls12_key_block *kb, SSL *s,
90 const EVP_AEAD *aead, const EVP_CIPHER *cipher, const EVP_MD *mac_hash)
91 {
92 size_t mac_key_len = 0, key_len = 0, iv_len = 0;
93 uint8_t *key_block = NULL;
94 size_t key_block_len = 0;
95 CBS cbs;
96
97 /*
98 * Generate a TLSv1.2 key block and partition into individual secrets,
99 * as per RFC 5246 section 6.3.
100 */
101
102 tls12_key_block_clear(kb);
103
104 /* Must have AEAD or cipher/MAC pair. */
105 if (aead == NULL && (cipher == NULL || mac_hash == NULL))
106 goto err;
107
108 if (aead != NULL) {
109 key_len = EVP_AEAD_key_length(aead);
110
111 /* AEAD fixed nonce length. */
112 if (aead == EVP_aead_aes_128_gcm() ||
113 aead == EVP_aead_aes_256_gcm())
114 iv_len = 4;
115 else if (aead == EVP_aead_chacha20_poly1305())
116 iv_len = 12;
117 else
118 goto err;
119 } else if (cipher != NULL && mac_hash != NULL) {
120 /*
121 * A negative integer return value will be detected via the
122 * EVP_MAX_* checks against the size_t variables below.
123 */
124 mac_key_len = EVP_MD_size(mac_hash);
125 key_len = EVP_CIPHER_key_length(cipher);
126 iv_len = EVP_CIPHER_iv_length(cipher);
127 }
128
129 if (mac_key_len > EVP_MAX_MD_SIZE)
130 goto err;
131 if (key_len > EVP_MAX_KEY_LENGTH)
132 goto err;
133 if (iv_len > EVP_MAX_IV_LENGTH)
134 goto err;
135
136 key_block_len = 2 * mac_key_len + 2 * key_len + 2 * iv_len;
137 if ((key_block = calloc(1, key_block_len)) == NULL)
138 goto err;
139
140 if (!tls1_generate_key_block(s, key_block, key_block_len))
141 goto err;
142
143 kb->key_block = key_block;
144 kb->key_block_len = key_block_len;
145 key_block = NULL;
146 key_block_len = 0;
147
148 /* Partition key block into individual secrets. */
149 CBS_init(&cbs, kb->key_block, kb->key_block_len);
150 if (!CBS_get_bytes(&cbs, &kb->client_write_mac_key, mac_key_len))
151 goto err;
152 if (!CBS_get_bytes(&cbs, &kb->server_write_mac_key, mac_key_len))
153 goto err;
154 if (!CBS_get_bytes(&cbs, &kb->client_write_key, key_len))
155 goto err;
156 if (!CBS_get_bytes(&cbs, &kb->server_write_key, key_len))
157 goto err;
158 if (!CBS_get_bytes(&cbs, &kb->client_write_iv, iv_len))
159 goto err;
160 if (!CBS_get_bytes(&cbs, &kb->server_write_iv, iv_len))
161 goto err;
162 if (CBS_len(&cbs) != 0)
163 goto err;
164
165 return 1;
166
167 err:
168 tls12_key_block_clear(kb);
169 freezero(key_block, key_block_len);
170
171 return 0;
172 }
173
174 struct tls12_reserved_label {
175 const char *label;
176 size_t label_len;
177 };
178
179 /*
180 * RFC 5705 section 6.
181 */
182 static const struct tls12_reserved_label tls12_reserved_labels[] = {
183 {
184 .label = TLS_MD_CLIENT_FINISH_CONST,
185 .label_len = TLS_MD_CLIENT_FINISH_CONST_SIZE,
186 },
187 {
188 .label = TLS_MD_SERVER_FINISH_CONST,
189 .label_len = TLS_MD_SERVER_FINISH_CONST_SIZE,
190 },
191 {
192 .label = TLS_MD_MASTER_SECRET_CONST,
193 .label_len = TLS_MD_MASTER_SECRET_CONST_SIZE,
194 },
195 {
196 .label = TLS_MD_KEY_EXPANSION_CONST,
197 .label_len = TLS_MD_KEY_EXPANSION_CONST_SIZE,
198 },
199 {
200 .label = NULL,
201 .label_len = 0,
202 },
203 };
204
205 int
tls12_exporter(SSL * s,const uint8_t * label,size_t label_len,const uint8_t * context_value,size_t context_value_len,int use_context,uint8_t * out,size_t out_len)206 tls12_exporter(SSL *s, const uint8_t *label, size_t label_len,
207 const uint8_t *context_value, size_t context_value_len, int use_context,
208 uint8_t *out, size_t out_len)
209 {
210 uint8_t *data = NULL;
211 size_t data_len = 0;
212 CBB cbb, context;
213 CBS seed;
214 size_t i;
215 int ret = 0;
216
217 /*
218 * RFC 5705 - Key Material Exporters for TLS.
219 */
220
221 memset(&cbb, 0, sizeof(cbb));
222
223 if (!SSL_is_init_finished(s)) {
224 SSLerror(s, SSL_R_BAD_STATE);
225 goto err;
226 }
227
228 if (s->s3->hs.negotiated_tls_version >= TLS1_3_VERSION)
229 goto err;
230
231 /*
232 * Due to exceptional design choices, we need to build a concatenation
233 * of the label and the seed value, before checking for reserved
234 * labels. This prevents a reserved label from being split across the
235 * label and the seed (that includes the client random), which are
236 * concatenated by the PRF.
237 */
238 if (!CBB_init(&cbb, 0))
239 goto err;
240 if (!CBB_add_bytes(&cbb, label, label_len))
241 goto err;
242 if (!CBB_add_bytes(&cbb, s->s3->client_random, SSL3_RANDOM_SIZE))
243 goto err;
244 if (!CBB_add_bytes(&cbb, s->s3->server_random, SSL3_RANDOM_SIZE))
245 goto err;
246 if (use_context) {
247 if (!CBB_add_u16_length_prefixed(&cbb, &context))
248 goto err;
249 if (context_value_len > 0) {
250 if (!CBB_add_bytes(&context, context_value,
251 context_value_len))
252 goto err;
253 }
254 }
255 if (!CBB_finish(&cbb, &data, &data_len))
256 goto err;
257
258 /*
259 * Ensure that the block (label + seed) does not start with a reserved
260 * label - in an ideal world we would ensure that the label has an
261 * explicitly permitted prefix instead, but of course this also got
262 * messed up by the standards.
263 */
264 for (i = 0; tls12_reserved_labels[i].label != NULL; i++) {
265 /* XXX - consider adding/using CBS_has_prefix(). */
266 if (tls12_reserved_labels[i].label_len > data_len)
267 goto err;
268 if (memcmp(data, tls12_reserved_labels[i].label,
269 tls12_reserved_labels[i].label_len) == 0) {
270 SSLerror(s, SSL_R_TLS_ILLEGAL_EXPORTER_LABEL);
271 goto err;
272 }
273 }
274
275 CBS_init(&seed, data, data_len);
276 if (!CBS_skip(&seed, label_len))
277 goto err;
278
279 if (!tls1_PRF(s, s->session->master_key, s->session->master_key_length,
280 label, label_len, CBS_data(&seed), CBS_len(&seed), NULL, 0, NULL, 0,
281 NULL, 0, out, out_len))
282 goto err;
283
284 ret = 1;
285
286 err:
287 freezero(data, data_len);
288 CBB_cleanup(&cbb);
289
290 return ret;
291 }
292