| /* Copyright (c) 2016, Google Inc. |
| * |
| * Permission to use, copy, modify, and/or distribute this software for any |
| * purpose with or without fee is hereby granted, provided that the above |
| * copyright notice and this permission notice appear in all copies. |
| * |
| * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES |
| * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF |
| * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY |
| * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES |
| * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION |
| * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN |
| * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ |
| |
| #include <openssl/ssl.h> |
| |
| #include <assert.h> |
| #include <string.h> |
| |
| #include <algorithm> |
| #include <utility> |
| |
| #include <openssl/aead.h> |
| #include <openssl/bytestring.h> |
| #include <openssl/digest.h> |
| #include <openssl/hkdf.h> |
| #include <openssl/hmac.h> |
| #include <openssl/mem.h> |
| |
| #include "../crypto/internal.h" |
| #include "internal.h" |
| |
| |
| BSSL_NAMESPACE_BEGIN |
| |
| static bool init_key_schedule(SSL_HANDSHAKE *hs, SSLTranscript *transcript, |
| uint16_t version, const SSL_CIPHER *cipher) { |
| if (!transcript->InitHash(version, cipher)) { |
| return false; |
| } |
| |
| // Initialize the secret to the zero key. |
| hs->ResizeSecrets(transcript->DigestLen()); |
| OPENSSL_memset(hs->secret().data(), 0, hs->secret().size()); |
| |
| return true; |
| } |
| |
| static bool hkdf_extract_to_secret(SSL_HANDSHAKE *hs, |
| const SSLTranscript &transcript, |
| Span<const uint8_t> in) { |
| size_t len; |
| if (!HKDF_extract(hs->secret().data(), &len, transcript.Digest(), in.data(), |
| in.size(), hs->secret().data(), hs->secret().size())) { |
| return false; |
| } |
| assert(len == hs->secret().size()); |
| return true; |
| } |
| |
| bool tls13_init_key_schedule(SSL_HANDSHAKE *hs, Span<const uint8_t> psk) { |
| if (!init_key_schedule(hs, &hs->transcript, ssl_protocol_version(hs->ssl), |
| hs->new_cipher)) { |
| return false; |
| } |
| |
| // Handback includes the whole handshake transcript, so we cannot free the |
| // transcript buffer in the handback case. |
| if (!hs->handback) { |
| hs->transcript.FreeBuffer(); |
| } |
| return hkdf_extract_to_secret(hs, hs->transcript, psk); |
| } |
| |
| bool tls13_init_early_key_schedule(SSL_HANDSHAKE *hs, |
| const SSL_SESSION *session) { |
| assert(!hs->ssl->server); |
| // When offering ECH, early data is associated with ClientHelloInner, not |
| // ClientHelloOuter. |
| SSLTranscript *transcript = |
| hs->selected_ech_config ? &hs->inner_transcript : &hs->transcript; |
| return init_key_schedule(hs, transcript, |
| ssl_session_protocol_version(session), |
| session->cipher) && |
| hkdf_extract_to_secret( |
| hs, *transcript, |
| MakeConstSpan(session->secret, session->secret_length)); |
| } |
| |
| static Span<const char> label_to_span(const char *label) { |
| return MakeConstSpan(label, strlen(label)); |
| } |
| |
| static bool 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) { |
| Span<const char> protocol_label = label_to_span("tls13 "); |
| ScopedCBB cbb; |
| CBB child; |
| Array<uint8_t> hkdf_label; |
| if (!CBB_init(cbb.get(), 2 + 1 + protocol_label.size() + label.size() + 1 + |
| hash.size()) || |
| !CBB_add_u16(cbb.get(), out.size()) || |
| !CBB_add_u8_length_prefixed(cbb.get(), &child) || |
| !CBB_add_bytes(&child, |
| reinterpret_cast<const uint8_t *>(protocol_label.data()), |
| protocol_label.size()) || |
| !CBB_add_bytes(&child, reinterpret_cast<const uint8_t *>(label.data()), |
| label.size()) || |
| !CBB_add_u8_length_prefixed(cbb.get(), &child) || |
| !CBB_add_bytes(&child, hash.data(), hash.size()) || |
| !CBBFinishArray(cbb.get(), &hkdf_label)) { |
| return false; |
| } |
| |
| return HKDF_expand(out.data(), out.size(), digest, secret.data(), |
| secret.size(), hkdf_label.data(), hkdf_label.size()); |
| } |
| |
| static const char kTLS13LabelDerived[] = "derived"; |
| |
| bool tls13_advance_key_schedule(SSL_HANDSHAKE *hs, Span<const uint8_t> in) { |
| uint8_t derive_context[EVP_MAX_MD_SIZE]; |
| unsigned derive_context_len; |
| return EVP_Digest(nullptr, 0, derive_context, &derive_context_len, |
| hs->transcript.Digest(), nullptr) && |
| hkdf_expand_label(hs->secret(), hs->transcript.Digest(), hs->secret(), |
| label_to_span(kTLS13LabelDerived), |
| MakeConstSpan(derive_context, derive_context_len)) && |
| hkdf_extract_to_secret(hs, hs->transcript, in); |
| } |
| |
| // derive_secret_with_transcript derives a secret of length |out.size()| and |
| // writes the result in |out| with the given label, the current base secret, and |
| // the state of |transcript|. It returns true on success and false on error. |
| static bool derive_secret_with_transcript(const SSL_HANDSHAKE *hs, |
| Span<uint8_t> out, |
| const SSLTranscript &transcript, |
| Span<const char> label) { |
| uint8_t context_hash[EVP_MAX_MD_SIZE]; |
| size_t context_hash_len; |
| if (!transcript.GetHash(context_hash, &context_hash_len)) { |
| return false; |
| } |
| |
| return hkdf_expand_label(out, transcript.Digest(), hs->secret(), label, |
| MakeConstSpan(context_hash, context_hash_len)); |
| } |
| |
| static bool derive_secret(SSL_HANDSHAKE *hs, Span<uint8_t> out, |
| Span<const char> label) { |
| return derive_secret_with_transcript(hs, out, hs->transcript, label); |
| } |
| |
| bool 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) { |
| uint16_t version = ssl_session_protocol_version(session); |
| UniquePtr<SSLAEADContext> traffic_aead; |
| Span<const uint8_t> secret_for_quic; |
| if (ssl->quic_method != nullptr) { |
| // Install a placeholder SSLAEADContext so that SSL accessors work. The |
| // encryption itself will be handled by the SSL_QUIC_METHOD. |
| traffic_aead = |
| SSLAEADContext::CreatePlaceholderForQUIC(version, session->cipher); |
| secret_for_quic = traffic_secret; |
| } else { |
| // Look up cipher suite properties. |
| const EVP_AEAD *aead; |
| size_t discard; |
| if (!ssl_cipher_get_evp_aead(&aead, &discard, &discard, session->cipher, |
| version, SSL_is_dtls(ssl))) { |
| return false; |
| } |
| |
| const EVP_MD *digest = ssl_session_get_digest(session); |
| |
| // Derive the key. |
| size_t key_len = EVP_AEAD_key_length(aead); |
| uint8_t key_buf[EVP_AEAD_MAX_KEY_LENGTH]; |
| auto key = MakeSpan(key_buf, key_len); |
| if (!hkdf_expand_label(key, digest, traffic_secret, label_to_span("key"), |
| {})) { |
| return false; |
| } |
| |
| // Derive the IV. |
| size_t iv_len = EVP_AEAD_nonce_length(aead); |
| uint8_t iv_buf[EVP_AEAD_MAX_NONCE_LENGTH]; |
| auto iv = MakeSpan(iv_buf, iv_len); |
| if (!hkdf_expand_label(iv, digest, traffic_secret, label_to_span("iv"), |
| {})) { |
| return false; |
| } |
| |
| traffic_aead = SSLAEADContext::Create(direction, session->ssl_version, |
| SSL_is_dtls(ssl), session->cipher, |
| key, Span<const uint8_t>(), iv); |
| } |
| |
| if (!traffic_aead) { |
| return false; |
| } |
| |
| if (traffic_secret.size() > |
| OPENSSL_ARRAY_SIZE(ssl->s3->read_traffic_secret) || |
| traffic_secret.size() > |
| OPENSSL_ARRAY_SIZE(ssl->s3->write_traffic_secret)) { |
| OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR); |
| return false; |
| } |
| |
| if (direction == evp_aead_open) { |
| if (!ssl->method->set_read_state(ssl, level, std::move(traffic_aead), |
| secret_for_quic)) { |
| return false; |
| } |
| OPENSSL_memmove(ssl->s3->read_traffic_secret, traffic_secret.data(), |
| traffic_secret.size()); |
| ssl->s3->read_traffic_secret_len = traffic_secret.size(); |
| } else { |
| if (!ssl->method->set_write_state(ssl, level, std::move(traffic_aead), |
| secret_for_quic)) { |
| return false; |
| } |
| OPENSSL_memmove(ssl->s3->write_traffic_secret, traffic_secret.data(), |
| traffic_secret.size()); |
| ssl->s3->write_traffic_secret_len = traffic_secret.size(); |
| } |
| |
| return true; |
| } |
| |
| |
| static const char kTLS13LabelExporter[] = "exp master"; |
| |
| static const char kTLS13LabelClientEarlyTraffic[] = "c e traffic"; |
| static const char kTLS13LabelClientHandshakeTraffic[] = "c hs traffic"; |
| static const char kTLS13LabelServerHandshakeTraffic[] = "s hs traffic"; |
| static const char kTLS13LabelClientApplicationTraffic[] = "c ap traffic"; |
| static const char kTLS13LabelServerApplicationTraffic[] = "s ap traffic"; |
| |
| bool tls13_derive_early_secret(SSL_HANDSHAKE *hs) { |
| SSL *const ssl = hs->ssl; |
| // When offering ECH on the client, early data is associated with |
| // ClientHelloInner, not ClientHelloOuter. |
| const SSLTranscript &transcript = (!ssl->server && hs->selected_ech_config) |
| ? hs->inner_transcript |
| : hs->transcript; |
| if (!derive_secret_with_transcript( |
| hs, hs->early_traffic_secret(), transcript, |
| label_to_span(kTLS13LabelClientEarlyTraffic)) || |
| !ssl_log_secret(ssl, "CLIENT_EARLY_TRAFFIC_SECRET", |
| hs->early_traffic_secret())) { |
| return false; |
| } |
| return true; |
| } |
| |
| bool tls13_derive_handshake_secrets(SSL_HANDSHAKE *hs) { |
| SSL *const ssl = hs->ssl; |
| if (!derive_secret(hs, hs->client_handshake_secret(), |
| label_to_span(kTLS13LabelClientHandshakeTraffic)) || |
| !ssl_log_secret(ssl, "CLIENT_HANDSHAKE_TRAFFIC_SECRET", |
| hs->client_handshake_secret()) || |
| !derive_secret(hs, hs->server_handshake_secret(), |
| label_to_span(kTLS13LabelServerHandshakeTraffic)) || |
| !ssl_log_secret(ssl, "SERVER_HANDSHAKE_TRAFFIC_SECRET", |
| hs->server_handshake_secret())) { |
| return false; |
| } |
| |
| return true; |
| } |
| |
| bool tls13_derive_application_secrets(SSL_HANDSHAKE *hs) { |
| SSL *const ssl = hs->ssl; |
| ssl->s3->exporter_secret_len = hs->transcript.DigestLen(); |
| if (!derive_secret(hs, hs->client_traffic_secret_0(), |
| label_to_span(kTLS13LabelClientApplicationTraffic)) || |
| !ssl_log_secret(ssl, "CLIENT_TRAFFIC_SECRET_0", |
| hs->client_traffic_secret_0()) || |
| !derive_secret(hs, hs->server_traffic_secret_0(), |
| label_to_span(kTLS13LabelServerApplicationTraffic)) || |
| !ssl_log_secret(ssl, "SERVER_TRAFFIC_SECRET_0", |
| hs->server_traffic_secret_0()) || |
| !derive_secret( |
| hs, MakeSpan(ssl->s3->exporter_secret, ssl->s3->exporter_secret_len), |
| label_to_span(kTLS13LabelExporter)) || |
| !ssl_log_secret(ssl, "EXPORTER_SECRET", |
| MakeConstSpan(ssl->s3->exporter_secret, |
| ssl->s3->exporter_secret_len))) { |
| return false; |
| } |
| |
| return true; |
| } |
| |
| static const char kTLS13LabelApplicationTraffic[] = "traffic upd"; |
| |
| bool tls13_rotate_traffic_key(SSL *ssl, enum evp_aead_direction_t direction) { |
| Span<uint8_t> secret; |
| if (direction == evp_aead_open) { |
| secret = MakeSpan(ssl->s3->read_traffic_secret, |
| ssl->s3->read_traffic_secret_len); |
| } else { |
| secret = MakeSpan(ssl->s3->write_traffic_secret, |
| ssl->s3->write_traffic_secret_len); |
| } |
| |
| const SSL_SESSION *session = SSL_get_session(ssl); |
| const EVP_MD *digest = ssl_session_get_digest(session); |
| return hkdf_expand_label(secret, digest, secret, |
| label_to_span(kTLS13LabelApplicationTraffic), {}) && |
| tls13_set_traffic_key(ssl, ssl_encryption_application, direction, |
| session, secret); |
| } |
| |
| static const char kTLS13LabelResumption[] = "res master"; |
| |
| bool tls13_derive_resumption_secret(SSL_HANDSHAKE *hs) { |
| if (hs->transcript.DigestLen() > SSL_MAX_MASTER_KEY_LENGTH) { |
| OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR); |
| return false; |
| } |
| hs->new_session->secret_length = hs->transcript.DigestLen(); |
| return derive_secret( |
| hs, MakeSpan(hs->new_session->secret, hs->new_session->secret_length), |
| label_to_span(kTLS13LabelResumption)); |
| } |
| |
| static const char kTLS13LabelFinished[] = "finished"; |
| |
| // tls13_verify_data sets |out| to be the HMAC of |context| using a derived |
| // Finished key for both Finished messages and the PSK binder. |out| must have |
| // space available for |EVP_MAX_MD_SIZE| bytes. |
| static bool 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) { |
| uint8_t key_buf[EVP_MAX_MD_SIZE]; |
| auto key = MakeSpan(key_buf, EVP_MD_size(digest)); |
| unsigned len; |
| if (!hkdf_expand_label(key, digest, secret, |
| label_to_span(kTLS13LabelFinished), {}) || |
| HMAC(digest, key.data(), key.size(), context.data(), context.size(), out, |
| &len) == nullptr) { |
| return false; |
| } |
| *out_len = len; |
| return true; |
| } |
| |
| bool tls13_finished_mac(SSL_HANDSHAKE *hs, uint8_t *out, size_t *out_len, |
| bool is_server) { |
| Span<const uint8_t> traffic_secret = |
| is_server ? hs->server_handshake_secret() : hs->client_handshake_secret(); |
| |
| uint8_t context_hash[EVP_MAX_MD_SIZE]; |
| size_t context_hash_len; |
| if (!hs->transcript.GetHash(context_hash, &context_hash_len) || |
| !tls13_verify_data(out, out_len, hs->transcript.Digest(), |
| hs->ssl->version, traffic_secret, |
| MakeConstSpan(context_hash, context_hash_len))) { |
| return 0; |
| } |
| return 1; |
| } |
| |
| static const char kTLS13LabelResumptionPSK[] = "resumption"; |
| |
| bool tls13_derive_session_psk(SSL_SESSION *session, Span<const uint8_t> nonce) { |
| const EVP_MD *digest = ssl_session_get_digest(session); |
| // The session initially stores the resumption_master_secret, which we |
| // override with the PSK. |
| auto session_secret = MakeSpan(session->secret, session->secret_length); |
| return hkdf_expand_label(session_secret, digest, session_secret, |
| label_to_span(kTLS13LabelResumptionPSK), nonce); |
| } |
| |
| static const char kTLS13LabelExportKeying[] = "exporter"; |
| |
| bool tls13_export_keying_material(SSL *ssl, Span<uint8_t> out, |
| Span<const uint8_t> secret, |
| Span<const char> label, |
| Span<const uint8_t> context) { |
| if (secret.empty()) { |
| assert(0); |
| OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR); |
| return false; |
| } |
| |
| const EVP_MD *digest = ssl_session_get_digest(SSL_get_session(ssl)); |
| |
| uint8_t hash_buf[EVP_MAX_MD_SIZE]; |
| uint8_t export_context_buf[EVP_MAX_MD_SIZE]; |
| unsigned hash_len; |
| unsigned export_context_len; |
| if (!EVP_Digest(context.data(), context.size(), hash_buf, &hash_len, digest, |
| nullptr) || |
| !EVP_Digest(nullptr, 0, export_context_buf, &export_context_len, digest, |
| nullptr)) { |
| return false; |
| } |
| |
| auto hash = MakeConstSpan(hash_buf, hash_len); |
| auto export_context = MakeConstSpan(export_context_buf, export_context_len); |
| uint8_t derived_secret_buf[EVP_MAX_MD_SIZE]; |
| auto derived_secret = MakeSpan(derived_secret_buf, EVP_MD_size(digest)); |
| return hkdf_expand_label(derived_secret, digest, secret, label, |
| export_context) && |
| hkdf_expand_label(out, digest, derived_secret, |
| label_to_span(kTLS13LabelExportKeying), hash); |
| } |
| |
| static const char kTLS13LabelPSKBinder[] = "res binder"; |
| |
| static bool 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) { |
| const EVP_MD *digest = ssl_session_get_digest(session); |
| |
| // Compute the binder key. |
| // |
| // TODO(davidben): Ideally we wouldn't recompute early secret and the binder |
| // key each time. |
| uint8_t binder_context[EVP_MAX_MD_SIZE]; |
| unsigned binder_context_len; |
| uint8_t early_secret[EVP_MAX_MD_SIZE] = {0}; |
| size_t early_secret_len; |
| uint8_t binder_key_buf[EVP_MAX_MD_SIZE] = {0}; |
| auto binder_key = MakeSpan(binder_key_buf, EVP_MD_size(digest)); |
| if (!EVP_Digest(nullptr, 0, binder_context, &binder_context_len, digest, |
| nullptr) || |
| !HKDF_extract(early_secret, &early_secret_len, digest, session->secret, |
| session->secret_length, nullptr, 0) || |
| !hkdf_expand_label(binder_key, digest, |
| MakeConstSpan(early_secret, early_secret_len), |
| label_to_span(kTLS13LabelPSKBinder), |
| MakeConstSpan(binder_context, binder_context_len))) { |
| return false; |
| } |
| |
| // Hash the transcript and truncated ClientHello. |
| if (client_hello.size() < binders_len) { |
| OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR); |
| return false; |
| } |
| auto truncated = client_hello.subspan(0, client_hello.size() - binders_len); |
| uint8_t context[EVP_MAX_MD_SIZE]; |
| unsigned context_len; |
| ScopedEVP_MD_CTX ctx; |
| if (!transcript.CopyToHashContext(ctx.get(), digest) || |
| !EVP_DigestUpdate(ctx.get(), truncated.data(), |
| truncated.size()) || |
| !EVP_DigestFinal_ex(ctx.get(), context, &context_len)) { |
| return false; |
| } |
| |
| if (!tls13_verify_data(out, out_len, digest, session->ssl_version, binder_key, |
| MakeConstSpan(context, context_len))) { |
| return false; |
| } |
| |
| assert(*out_len == EVP_MD_size(digest)); |
| return true; |
| } |
| |
| bool tls13_write_psk_binder(const SSL_HANDSHAKE *hs, |
| const SSLTranscript &transcript, Span<uint8_t> msg, |
| size_t *out_binder_len) { |
| const SSL *const ssl = hs->ssl; |
| const EVP_MD *digest = ssl_session_get_digest(ssl->session.get()); |
| const size_t hash_len = EVP_MD_size(digest); |
| // We only offer one PSK, so the binders are a u16 and u8 length |
| // prefix, followed by the binder. The caller is assumed to have constructed |
| // |msg| with placeholder binders. |
| const size_t binders_len = 3 + hash_len; |
| uint8_t verify_data[EVP_MAX_MD_SIZE]; |
| size_t verify_data_len; |
| if (!tls13_psk_binder(verify_data, &verify_data_len, ssl->session.get(), |
| transcript, msg, binders_len) || |
| verify_data_len != hash_len) { |
| OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR); |
| return false; |
| } |
| |
| OPENSSL_memcpy(msg.data() + msg.size() - verify_data_len, verify_data, |
| verify_data_len); |
| if (out_binder_len != nullptr) { |
| *out_binder_len = verify_data_len; |
| } |
| return true; |
| } |
| |
| bool tls13_verify_psk_binder(const SSL_HANDSHAKE *hs, |
| const SSL_SESSION *session, const SSLMessage &msg, |
| CBS *binders) { |
| uint8_t verify_data[EVP_MAX_MD_SIZE]; |
| size_t verify_data_len; |
| CBS binder; |
| // The binders are computed over |msg| with |binders| and its u16 length |
| // prefix removed. The caller is assumed to have parsed |msg|, extracted |
| // |binders|, and verified the PSK extension is last. |
| if (!tls13_psk_binder(verify_data, &verify_data_len, session, hs->transcript, |
| msg.raw, 2 + CBS_len(binders)) || |
| // We only consider the first PSK, so compare against the first binder. |
| !CBS_get_u8_length_prefixed(binders, &binder)) { |
| OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR); |
| return false; |
| } |
| |
| bool binder_ok = |
| CBS_len(&binder) == verify_data_len && |
| CRYPTO_memcmp(CBS_data(&binder), verify_data, verify_data_len) == 0; |
| #if defined(BORINGSSL_UNSAFE_FUZZER_MODE) |
| binder_ok = true; |
| #endif |
| if (!binder_ok) { |
| OPENSSL_PUT_ERROR(SSL, SSL_R_DIGEST_CHECK_FAILED); |
| return false; |
| } |
| |
| return true; |
| } |
| |
| size_t ssl_ech_confirmation_signal_hello_offset(const SSL *ssl) { |
| static_assert(ECH_CONFIRMATION_SIGNAL_LEN < SSL3_RANDOM_SIZE, |
| "the confirmation signal is a suffix of the random"); |
| const size_t header_len = |
| SSL_is_dtls(ssl) ? DTLS1_HM_HEADER_LENGTH : SSL3_HM_HEADER_LENGTH; |
| return header_len + 2 /* version */ + SSL3_RANDOM_SIZE - |
| ECH_CONFIRMATION_SIGNAL_LEN; |
| } |
| |
| bool ssl_ech_accept_confirmation( |
| const SSL_HANDSHAKE *hs, bssl::Span<uint8_t> out, |
| const SSLTranscript &transcript, |
| bssl::Span<const uint8_t> server_hello) { |
| // We hash |server_hello|, with the last |ECH_CONFIRMATION_SIGNAL_LEN| bytes |
| // of the random value zeroed. |
| static const uint8_t kZeroes[ECH_CONFIRMATION_SIGNAL_LEN] = {0}; |
| const size_t offset = ssl_ech_confirmation_signal_hello_offset(hs->ssl); |
| if (server_hello.size() < offset + ECH_CONFIRMATION_SIGNAL_LEN) { |
| OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR); |
| return false; |
| } |
| |
| auto before_zeroes = server_hello.subspan(0, offset); |
| auto after_zeroes = |
| server_hello.subspan(offset + ECH_CONFIRMATION_SIGNAL_LEN); |
| uint8_t context_hash[EVP_MAX_MD_SIZE]; |
| unsigned context_hash_len; |
| ScopedEVP_MD_CTX ctx; |
| if (!transcript.CopyToHashContext(ctx.get(), transcript.Digest()) || |
| !EVP_DigestUpdate(ctx.get(), before_zeroes.data(), |
| before_zeroes.size()) || |
| !EVP_DigestUpdate(ctx.get(), kZeroes, sizeof(kZeroes)) || |
| !EVP_DigestUpdate(ctx.get(), after_zeroes.data(), after_zeroes.size()) || |
| !EVP_DigestFinal_ex(ctx.get(), context_hash, &context_hash_len)) { |
| return false; |
| } |
| |
| // Per draft-ietf-tls-esni-10, accept_confirmation is computed with |
| // Derive-Secret, which derives a secret of size Hash.length. That value is |
| // then truncated to the first 8 bytes. Note this differs from deriving an |
| // 8-byte secret because the target length is included in the derivation. |
| // |
| // TODO(https://crbug.com/boringssl/275): draft-11 will avoid this. |
| uint8_t accept_confirmation_buf[EVP_MAX_MD_SIZE]; |
| bssl::Span<uint8_t> accept_confirmation = |
| MakeSpan(accept_confirmation_buf, transcript.DigestLen()); |
| if (!hkdf_expand_label(accept_confirmation, transcript.Digest(), |
| hs->secret(), label_to_span("ech accept confirmation"), |
| MakeConstSpan(context_hash, context_hash_len))) { |
| return false; |
| } |
| |
| static_assert(ECH_CONFIRMATION_SIGNAL_LEN < EVP_MAX_MD_SIZE, |
| "ECH confirmation signal too big"); |
| if (out.size() != ECH_CONFIRMATION_SIGNAL_LEN) { |
| OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR); |
| return false; |
| } |
| OPENSSL_memcpy(out.data(), accept_confirmation.data(), out.size()); |
| return true; |
| } |
| |
| BSSL_NAMESPACE_END |