1 /* Copyright (c) 2016, Google Inc.
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15 #include <openssl/ssl.h>
16
17 #include <assert.h>
18 #include <string.h>
19
20 #include <algorithm>
21 #include <utility>
22
23 #include <openssl/aead.h>
24 #include <openssl/bytestring.h>
25 #include <openssl/digest.h>
26 #include <openssl/hkdf.h>
27 #include <openssl/hmac.h>
28 #include <openssl/mem.h>
29
30 #include "../crypto/fipsmodule/tls/internal.h"
31 #include "../crypto/internal.h"
32 #include "internal.h"
33
34
35 BSSL_NAMESPACE_BEGIN
36
init_key_schedule(SSL_HANDSHAKE * hs,SSLTranscript * transcript,uint16_t version,const SSL_CIPHER * cipher)37 static bool init_key_schedule(SSL_HANDSHAKE *hs, SSLTranscript *transcript,
38 uint16_t version, const SSL_CIPHER *cipher) {
39 if (!transcript->InitHash(version, cipher)) {
40 return false;
41 }
42
43 // Initialize the secret to the zero key.
44 hs->ResizeSecrets(transcript->DigestLen());
45 OPENSSL_memset(hs->secret().data(), 0, hs->secret().size());
46
47 return true;
48 }
49
hkdf_extract_to_secret(SSL_HANDSHAKE * hs,const SSLTranscript & transcript,Span<const uint8_t> in)50 static bool hkdf_extract_to_secret(SSL_HANDSHAKE *hs,
51 const SSLTranscript &transcript,
52 Span<const uint8_t> in) {
53 size_t len;
54 if (!HKDF_extract(hs->secret().data(), &len, transcript.Digest(), in.data(),
55 in.size(), hs->secret().data(), hs->secret().size())) {
56 return false;
57 }
58 assert(len == hs->secret().size());
59 return true;
60 }
61
tls13_init_key_schedule(SSL_HANDSHAKE * hs,Span<const uint8_t> psk)62 bool tls13_init_key_schedule(SSL_HANDSHAKE *hs, Span<const uint8_t> psk) {
63 if (!init_key_schedule(hs, &hs->transcript, ssl_protocol_version(hs->ssl),
64 hs->new_cipher)) {
65 return false;
66 }
67
68 // Handback includes the whole handshake transcript, so we cannot free the
69 // transcript buffer in the handback case.
70 if (!hs->handback) {
71 hs->transcript.FreeBuffer();
72 }
73 return hkdf_extract_to_secret(hs, hs->transcript, psk);
74 }
75
tls13_init_early_key_schedule(SSL_HANDSHAKE * hs,const SSL_SESSION * session)76 bool tls13_init_early_key_schedule(SSL_HANDSHAKE *hs,
77 const SSL_SESSION *session) {
78 assert(!hs->ssl->server);
79 // When offering ECH, early data is associated with ClientHelloInner, not
80 // ClientHelloOuter.
81 SSLTranscript *transcript =
82 hs->selected_ech_config ? &hs->inner_transcript : &hs->transcript;
83 return init_key_schedule(hs, transcript,
84 ssl_session_protocol_version(session),
85 session->cipher) &&
86 hkdf_extract_to_secret(
87 hs, *transcript,
88 MakeConstSpan(session->secret, session->secret_length));
89 }
90
label_to_span(const char * label)91 static Span<const char> label_to_span(const char *label) {
92 return MakeConstSpan(label, strlen(label));
93 }
94
hkdf_expand_label(Span<uint8_t> out,const EVP_MD * digest,Span<const uint8_t> secret,Span<const char> label,Span<const uint8_t> hash)95 static bool hkdf_expand_label(Span<uint8_t> out, const EVP_MD *digest,
96 Span<const uint8_t> secret,
97 Span<const char> label,
98 Span<const uint8_t> hash) {
99 return CRYPTO_tls13_hkdf_expand_label(
100 out.data(), out.size(), digest, secret.data(), secret.size(),
101 reinterpret_cast<const uint8_t *>(label.data()), label.size(),
102 hash.data(), hash.size()) == 1;
103 }
104
105 static const char kTLS13LabelDerived[] = "derived";
106
tls13_advance_key_schedule(SSL_HANDSHAKE * hs,Span<const uint8_t> in)107 bool tls13_advance_key_schedule(SSL_HANDSHAKE *hs, Span<const uint8_t> in) {
108 uint8_t derive_context[EVP_MAX_MD_SIZE];
109 unsigned derive_context_len;
110 return EVP_Digest(nullptr, 0, derive_context, &derive_context_len,
111 hs->transcript.Digest(), nullptr) &&
112 hkdf_expand_label(hs->secret(), hs->transcript.Digest(), hs->secret(),
113 label_to_span(kTLS13LabelDerived),
114 MakeConstSpan(derive_context, derive_context_len)) &&
115 hkdf_extract_to_secret(hs, hs->transcript, in);
116 }
117
118 // derive_secret_with_transcript derives a secret of length |out.size()| and
119 // writes the result in |out| with the given label, the current base secret, and
120 // the state of |transcript|. It returns true on success and false on error.
derive_secret_with_transcript(const SSL_HANDSHAKE * hs,Span<uint8_t> out,const SSLTranscript & transcript,Span<const char> label)121 static bool derive_secret_with_transcript(const SSL_HANDSHAKE *hs,
122 Span<uint8_t> out,
123 const SSLTranscript &transcript,
124 Span<const char> label) {
125 uint8_t context_hash[EVP_MAX_MD_SIZE];
126 size_t context_hash_len;
127 if (!transcript.GetHash(context_hash, &context_hash_len)) {
128 return false;
129 }
130
131 return hkdf_expand_label(out, transcript.Digest(), hs->secret(), label,
132 MakeConstSpan(context_hash, context_hash_len));
133 }
134
derive_secret(SSL_HANDSHAKE * hs,Span<uint8_t> out,Span<const char> label)135 static bool derive_secret(SSL_HANDSHAKE *hs, Span<uint8_t> out,
136 Span<const char> label) {
137 return derive_secret_with_transcript(hs, out, hs->transcript, label);
138 }
139
tls13_set_traffic_key(SSL * ssl,enum ssl_encryption_level_t level,enum evp_aead_direction_t direction,const SSL_SESSION * session,Span<const uint8_t> traffic_secret)140 bool tls13_set_traffic_key(SSL *ssl, enum ssl_encryption_level_t level,
141 enum evp_aead_direction_t direction,
142 const SSL_SESSION *session,
143 Span<const uint8_t> traffic_secret) {
144 uint16_t version = ssl_session_protocol_version(session);
145 UniquePtr<SSLAEADContext> traffic_aead;
146 Span<const uint8_t> secret_for_quic;
147 if (ssl->quic_method != nullptr) {
148 // Install a placeholder SSLAEADContext so that SSL accessors work. The
149 // encryption itself will be handled by the SSL_QUIC_METHOD.
150 traffic_aead =
151 SSLAEADContext::CreatePlaceholderForQUIC(version, session->cipher);
152 secret_for_quic = traffic_secret;
153 } else {
154 // Look up cipher suite properties.
155 const EVP_AEAD *aead;
156 size_t discard;
157 if (!ssl_cipher_get_evp_aead(&aead, &discard, &discard, session->cipher,
158 version, SSL_is_dtls(ssl))) {
159 return false;
160 }
161
162 const EVP_MD *digest = ssl_session_get_digest(session);
163
164 // Derive the key.
165 size_t key_len = EVP_AEAD_key_length(aead);
166 uint8_t key_buf[EVP_AEAD_MAX_KEY_LENGTH];
167 auto key = MakeSpan(key_buf, key_len);
168 if (!hkdf_expand_label(key, digest, traffic_secret, label_to_span("key"),
169 {})) {
170 return false;
171 }
172
173 // Derive the IV.
174 size_t iv_len = EVP_AEAD_nonce_length(aead);
175 uint8_t iv_buf[EVP_AEAD_MAX_NONCE_LENGTH];
176 auto iv = MakeSpan(iv_buf, iv_len);
177 if (!hkdf_expand_label(iv, digest, traffic_secret, label_to_span("iv"),
178 {})) {
179 return false;
180 }
181
182 traffic_aead = SSLAEADContext::Create(direction, session->ssl_version,
183 SSL_is_dtls(ssl), session->cipher,
184 key, Span<const uint8_t>(), iv);
185 }
186
187 if (!traffic_aead) {
188 return false;
189 }
190
191 if (traffic_secret.size() >
192 OPENSSL_ARRAY_SIZE(ssl->s3->read_traffic_secret) ||
193 traffic_secret.size() >
194 OPENSSL_ARRAY_SIZE(ssl->s3->write_traffic_secret)) {
195 OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
196 return false;
197 }
198
199 if (direction == evp_aead_open) {
200 if (!ssl->method->set_read_state(ssl, level, std::move(traffic_aead),
201 secret_for_quic)) {
202 return false;
203 }
204 OPENSSL_memmove(ssl->s3->read_traffic_secret, traffic_secret.data(),
205 traffic_secret.size());
206 ssl->s3->read_traffic_secret_len = traffic_secret.size();
207 } else {
208 if (!ssl->method->set_write_state(ssl, level, std::move(traffic_aead),
209 secret_for_quic)) {
210 return false;
211 }
212 OPENSSL_memmove(ssl->s3->write_traffic_secret, traffic_secret.data(),
213 traffic_secret.size());
214 ssl->s3->write_traffic_secret_len = traffic_secret.size();
215 }
216
217 return true;
218 }
219
220
221 static const char kTLS13LabelExporter[] = "exp master";
222
223 static const char kTLS13LabelClientEarlyTraffic[] = "c e traffic";
224 static const char kTLS13LabelClientHandshakeTraffic[] = "c hs traffic";
225 static const char kTLS13LabelServerHandshakeTraffic[] = "s hs traffic";
226 static const char kTLS13LabelClientApplicationTraffic[] = "c ap traffic";
227 static const char kTLS13LabelServerApplicationTraffic[] = "s ap traffic";
228
tls13_derive_early_secret(SSL_HANDSHAKE * hs)229 bool tls13_derive_early_secret(SSL_HANDSHAKE *hs) {
230 SSL *const ssl = hs->ssl;
231 // When offering ECH on the client, early data is associated with
232 // ClientHelloInner, not ClientHelloOuter.
233 const SSLTranscript &transcript = (!ssl->server && hs->selected_ech_config)
234 ? hs->inner_transcript
235 : hs->transcript;
236 if (!derive_secret_with_transcript(
237 hs, hs->early_traffic_secret(), transcript,
238 label_to_span(kTLS13LabelClientEarlyTraffic)) ||
239 !ssl_log_secret(ssl, "CLIENT_EARLY_TRAFFIC_SECRET",
240 hs->early_traffic_secret())) {
241 return false;
242 }
243 return true;
244 }
245
tls13_derive_handshake_secrets(SSL_HANDSHAKE * hs)246 bool tls13_derive_handshake_secrets(SSL_HANDSHAKE *hs) {
247 SSL *const ssl = hs->ssl;
248 if (!derive_secret(hs, hs->client_handshake_secret(),
249 label_to_span(kTLS13LabelClientHandshakeTraffic)) ||
250 !ssl_log_secret(ssl, "CLIENT_HANDSHAKE_TRAFFIC_SECRET",
251 hs->client_handshake_secret()) ||
252 !derive_secret(hs, hs->server_handshake_secret(),
253 label_to_span(kTLS13LabelServerHandshakeTraffic)) ||
254 !ssl_log_secret(ssl, "SERVER_HANDSHAKE_TRAFFIC_SECRET",
255 hs->server_handshake_secret())) {
256 return false;
257 }
258
259 return true;
260 }
261
tls13_derive_application_secrets(SSL_HANDSHAKE * hs)262 bool tls13_derive_application_secrets(SSL_HANDSHAKE *hs) {
263 SSL *const ssl = hs->ssl;
264 ssl->s3->exporter_secret_len = hs->transcript.DigestLen();
265 if (!derive_secret(hs, hs->client_traffic_secret_0(),
266 label_to_span(kTLS13LabelClientApplicationTraffic)) ||
267 !ssl_log_secret(ssl, "CLIENT_TRAFFIC_SECRET_0",
268 hs->client_traffic_secret_0()) ||
269 !derive_secret(hs, hs->server_traffic_secret_0(),
270 label_to_span(kTLS13LabelServerApplicationTraffic)) ||
271 !ssl_log_secret(ssl, "SERVER_TRAFFIC_SECRET_0",
272 hs->server_traffic_secret_0()) ||
273 !derive_secret(
274 hs, MakeSpan(ssl->s3->exporter_secret, ssl->s3->exporter_secret_len),
275 label_to_span(kTLS13LabelExporter)) ||
276 !ssl_log_secret(ssl, "EXPORTER_SECRET",
277 MakeConstSpan(ssl->s3->exporter_secret,
278 ssl->s3->exporter_secret_len))) {
279 return false;
280 }
281
282 return true;
283 }
284
285 static const char kTLS13LabelApplicationTraffic[] = "traffic upd";
286
tls13_rotate_traffic_key(SSL * ssl,enum evp_aead_direction_t direction)287 bool tls13_rotate_traffic_key(SSL *ssl, enum evp_aead_direction_t direction) {
288 Span<uint8_t> secret;
289 if (direction == evp_aead_open) {
290 secret = MakeSpan(ssl->s3->read_traffic_secret,
291 ssl->s3->read_traffic_secret_len);
292 } else {
293 secret = MakeSpan(ssl->s3->write_traffic_secret,
294 ssl->s3->write_traffic_secret_len);
295 }
296
297 const SSL_SESSION *session = SSL_get_session(ssl);
298 const EVP_MD *digest = ssl_session_get_digest(session);
299 return hkdf_expand_label(secret, digest, secret,
300 label_to_span(kTLS13LabelApplicationTraffic), {}) &&
301 tls13_set_traffic_key(ssl, ssl_encryption_application, direction,
302 session, secret);
303 }
304
305 static const char kTLS13LabelResumption[] = "res master";
306
tls13_derive_resumption_secret(SSL_HANDSHAKE * hs)307 bool tls13_derive_resumption_secret(SSL_HANDSHAKE *hs) {
308 if (hs->transcript.DigestLen() > SSL_MAX_MASTER_KEY_LENGTH) {
309 OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
310 return false;
311 }
312 hs->new_session->secret_length = hs->transcript.DigestLen();
313 return derive_secret(
314 hs, MakeSpan(hs->new_session->secret, hs->new_session->secret_length),
315 label_to_span(kTLS13LabelResumption));
316 }
317
318 static const char kTLS13LabelFinished[] = "finished";
319
320 // tls13_verify_data sets |out| to be the HMAC of |context| using a derived
321 // Finished key for both Finished messages and the PSK binder. |out| must have
322 // space available for |EVP_MAX_MD_SIZE| bytes.
tls13_verify_data(uint8_t * out,size_t * out_len,const EVP_MD * digest,uint16_t version,Span<const uint8_t> secret,Span<const uint8_t> context)323 static bool tls13_verify_data(uint8_t *out, size_t *out_len,
324 const EVP_MD *digest, uint16_t version,
325 Span<const uint8_t> secret,
326 Span<const uint8_t> context) {
327 uint8_t key_buf[EVP_MAX_MD_SIZE];
328 auto key = MakeSpan(key_buf, EVP_MD_size(digest));
329 unsigned len;
330 if (!hkdf_expand_label(key, digest, secret,
331 label_to_span(kTLS13LabelFinished), {}) ||
332 HMAC(digest, key.data(), key.size(), context.data(), context.size(), out,
333 &len) == nullptr) {
334 return false;
335 }
336 *out_len = len;
337 return true;
338 }
339
tls13_finished_mac(SSL_HANDSHAKE * hs,uint8_t * out,size_t * out_len,bool is_server)340 bool tls13_finished_mac(SSL_HANDSHAKE *hs, uint8_t *out, size_t *out_len,
341 bool is_server) {
342 Span<const uint8_t> traffic_secret =
343 is_server ? hs->server_handshake_secret() : hs->client_handshake_secret();
344
345 uint8_t context_hash[EVP_MAX_MD_SIZE];
346 size_t context_hash_len;
347 if (!hs->transcript.GetHash(context_hash, &context_hash_len) ||
348 !tls13_verify_data(out, out_len, hs->transcript.Digest(),
349 hs->ssl->version, traffic_secret,
350 MakeConstSpan(context_hash, context_hash_len))) {
351 return false;
352 }
353 return true;
354 }
355
356 static const char kTLS13LabelResumptionPSK[] = "resumption";
357
tls13_derive_session_psk(SSL_SESSION * session,Span<const uint8_t> nonce)358 bool tls13_derive_session_psk(SSL_SESSION *session, Span<const uint8_t> nonce) {
359 const EVP_MD *digest = ssl_session_get_digest(session);
360 // The session initially stores the resumption_master_secret, which we
361 // override with the PSK.
362 auto session_secret = MakeSpan(session->secret, session->secret_length);
363 return hkdf_expand_label(session_secret, digest, session_secret,
364 label_to_span(kTLS13LabelResumptionPSK), nonce);
365 }
366
367 static const char kTLS13LabelExportKeying[] = "exporter";
368
tls13_export_keying_material(SSL * ssl,Span<uint8_t> out,Span<const uint8_t> secret,Span<const char> label,Span<const uint8_t> context)369 bool tls13_export_keying_material(SSL *ssl, Span<uint8_t> out,
370 Span<const uint8_t> secret,
371 Span<const char> label,
372 Span<const uint8_t> context) {
373 if (secret.empty()) {
374 assert(0);
375 OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
376 return false;
377 }
378
379 const EVP_MD *digest = ssl_session_get_digest(SSL_get_session(ssl));
380
381 uint8_t hash_buf[EVP_MAX_MD_SIZE];
382 uint8_t export_context_buf[EVP_MAX_MD_SIZE];
383 unsigned hash_len;
384 unsigned export_context_len;
385 if (!EVP_Digest(context.data(), context.size(), hash_buf, &hash_len, digest,
386 nullptr) ||
387 !EVP_Digest(nullptr, 0, export_context_buf, &export_context_len, digest,
388 nullptr)) {
389 return false;
390 }
391
392 auto hash = MakeConstSpan(hash_buf, hash_len);
393 auto export_context = MakeConstSpan(export_context_buf, export_context_len);
394 uint8_t derived_secret_buf[EVP_MAX_MD_SIZE];
395 auto derived_secret = MakeSpan(derived_secret_buf, EVP_MD_size(digest));
396 return hkdf_expand_label(derived_secret, digest, secret, label,
397 export_context) &&
398 hkdf_expand_label(out, digest, derived_secret,
399 label_to_span(kTLS13LabelExportKeying), hash);
400 }
401
402 static const char kTLS13LabelPSKBinder[] = "res binder";
403
tls13_psk_binder(uint8_t * out,size_t * out_len,const SSL_SESSION * session,const SSLTranscript & transcript,Span<const uint8_t> client_hello,size_t binders_len)404 static bool tls13_psk_binder(uint8_t *out, size_t *out_len,
405 const SSL_SESSION *session,
406 const SSLTranscript &transcript,
407 Span<const uint8_t> client_hello,
408 size_t binders_len) {
409 const EVP_MD *digest = ssl_session_get_digest(session);
410
411 // Compute the binder key.
412 //
413 // TODO(davidben): Ideally we wouldn't recompute early secret and the binder
414 // key each time.
415 uint8_t binder_context[EVP_MAX_MD_SIZE];
416 unsigned binder_context_len;
417 uint8_t early_secret[EVP_MAX_MD_SIZE] = {0};
418 size_t early_secret_len;
419 uint8_t binder_key_buf[EVP_MAX_MD_SIZE] = {0};
420 auto binder_key = MakeSpan(binder_key_buf, EVP_MD_size(digest));
421 if (!EVP_Digest(nullptr, 0, binder_context, &binder_context_len, digest,
422 nullptr) ||
423 !HKDF_extract(early_secret, &early_secret_len, digest, session->secret,
424 session->secret_length, nullptr, 0) ||
425 !hkdf_expand_label(binder_key, digest,
426 MakeConstSpan(early_secret, early_secret_len),
427 label_to_span(kTLS13LabelPSKBinder),
428 MakeConstSpan(binder_context, binder_context_len))) {
429 return false;
430 }
431
432 // Hash the transcript and truncated ClientHello.
433 if (client_hello.size() < binders_len) {
434 OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
435 return false;
436 }
437 auto truncated = client_hello.subspan(0, client_hello.size() - binders_len);
438 uint8_t context[EVP_MAX_MD_SIZE];
439 unsigned context_len;
440 ScopedEVP_MD_CTX ctx;
441 if (!transcript.CopyToHashContext(ctx.get(), digest) ||
442 !EVP_DigestUpdate(ctx.get(), truncated.data(),
443 truncated.size()) ||
444 !EVP_DigestFinal_ex(ctx.get(), context, &context_len)) {
445 return false;
446 }
447
448 if (!tls13_verify_data(out, out_len, digest, session->ssl_version, binder_key,
449 MakeConstSpan(context, context_len))) {
450 return false;
451 }
452
453 assert(*out_len == EVP_MD_size(digest));
454 return true;
455 }
456
tls13_write_psk_binder(const SSL_HANDSHAKE * hs,const SSLTranscript & transcript,Span<uint8_t> msg,size_t * out_binder_len)457 bool tls13_write_psk_binder(const SSL_HANDSHAKE *hs,
458 const SSLTranscript &transcript, Span<uint8_t> msg,
459 size_t *out_binder_len) {
460 const SSL *const ssl = hs->ssl;
461 const EVP_MD *digest = ssl_session_get_digest(ssl->session.get());
462 const size_t hash_len = EVP_MD_size(digest);
463 // We only offer one PSK, so the binders are a u16 and u8 length
464 // prefix, followed by the binder. The caller is assumed to have constructed
465 // |msg| with placeholder binders.
466 const size_t binders_len = 3 + hash_len;
467 uint8_t verify_data[EVP_MAX_MD_SIZE];
468 size_t verify_data_len;
469 if (!tls13_psk_binder(verify_data, &verify_data_len, ssl->session.get(),
470 transcript, msg, binders_len) ||
471 verify_data_len != hash_len) {
472 OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
473 return false;
474 }
475
476 auto msg_binder = msg.last(verify_data_len);
477 OPENSSL_memcpy(msg_binder.data(), verify_data, verify_data_len);
478 if (out_binder_len != nullptr) {
479 *out_binder_len = verify_data_len;
480 }
481 return true;
482 }
483
tls13_verify_psk_binder(const SSL_HANDSHAKE * hs,const SSL_SESSION * session,const SSLMessage & msg,CBS * binders)484 bool tls13_verify_psk_binder(const SSL_HANDSHAKE *hs,
485 const SSL_SESSION *session, const SSLMessage &msg,
486 CBS *binders) {
487 uint8_t verify_data[EVP_MAX_MD_SIZE];
488 size_t verify_data_len;
489 CBS binder;
490 // The binders are computed over |msg| with |binders| and its u16 length
491 // prefix removed. The caller is assumed to have parsed |msg|, extracted
492 // |binders|, and verified the PSK extension is last.
493 if (!tls13_psk_binder(verify_data, &verify_data_len, session, hs->transcript,
494 msg.raw, 2 + CBS_len(binders)) ||
495 // We only consider the first PSK, so compare against the first binder.
496 !CBS_get_u8_length_prefixed(binders, &binder)) {
497 OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
498 return false;
499 }
500
501 bool binder_ok =
502 CBS_len(&binder) == verify_data_len &&
503 CRYPTO_memcmp(CBS_data(&binder), verify_data, verify_data_len) == 0;
504 #if defined(BORINGSSL_UNSAFE_FUZZER_MODE)
505 binder_ok = true;
506 #endif
507 if (!binder_ok) {
508 OPENSSL_PUT_ERROR(SSL, SSL_R_DIGEST_CHECK_FAILED);
509 return false;
510 }
511
512 return true;
513 }
514
ssl_ech_confirmation_signal_hello_offset(const SSL * ssl)515 size_t ssl_ech_confirmation_signal_hello_offset(const SSL *ssl) {
516 static_assert(ECH_CONFIRMATION_SIGNAL_LEN < SSL3_RANDOM_SIZE,
517 "the confirmation signal is a suffix of the random");
518 const size_t header_len =
519 SSL_is_dtls(ssl) ? DTLS1_HM_HEADER_LENGTH : SSL3_HM_HEADER_LENGTH;
520 return header_len + 2 /* version */ + SSL3_RANDOM_SIZE -
521 ECH_CONFIRMATION_SIGNAL_LEN;
522 }
523
ssl_ech_accept_confirmation(const SSL_HANDSHAKE * hs,Span<uint8_t> out,Span<const uint8_t> client_random,const SSLTranscript & transcript,bool is_hrr,Span<const uint8_t> msg,size_t offset)524 bool ssl_ech_accept_confirmation(const SSL_HANDSHAKE *hs, Span<uint8_t> out,
525 Span<const uint8_t> client_random,
526 const SSLTranscript &transcript, bool is_hrr,
527 Span<const uint8_t> msg, size_t offset) {
528 // See draft-ietf-tls-esni-13, sections 7.2 and 7.2.1.
529 static const uint8_t kZeros[EVP_MAX_MD_SIZE] = {0};
530
531 // We hash |msg|, with bytes from |offset| zeroed.
532 if (msg.size() < offset + ECH_CONFIRMATION_SIGNAL_LEN) {
533 OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
534 return false;
535 }
536
537 auto before_zeros = msg.subspan(0, offset);
538 auto after_zeros = msg.subspan(offset + ECH_CONFIRMATION_SIGNAL_LEN);
539 uint8_t context[EVP_MAX_MD_SIZE];
540 unsigned context_len;
541 ScopedEVP_MD_CTX ctx;
542 if (!transcript.CopyToHashContext(ctx.get(), transcript.Digest()) ||
543 !EVP_DigestUpdate(ctx.get(), before_zeros.data(), before_zeros.size()) ||
544 !EVP_DigestUpdate(ctx.get(), kZeros, ECH_CONFIRMATION_SIGNAL_LEN) ||
545 !EVP_DigestUpdate(ctx.get(), after_zeros.data(), after_zeros.size()) ||
546 !EVP_DigestFinal_ex(ctx.get(), context, &context_len)) {
547 return false;
548 }
549
550 uint8_t secret[EVP_MAX_MD_SIZE];
551 size_t secret_len;
552 if (!HKDF_extract(secret, &secret_len, transcript.Digest(),
553 client_random.data(), client_random.size(), kZeros,
554 transcript.DigestLen())) {
555 return false;
556 }
557
558 assert(out.size() == ECH_CONFIRMATION_SIGNAL_LEN);
559 return hkdf_expand_label(out, transcript.Digest(),
560 MakeConstSpan(secret, secret_len),
561 is_hrr ? label_to_span("hrr ech accept confirmation")
562 : label_to_span("ech accept confirmation"),
563 MakeConstSpan(context, context_len));
564 }
565
566 BSSL_NAMESPACE_END
567