ssl/tls13_enc.cc - boringssl - Git at Google

 /* 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, uint16_t version,
                               const SSL_CIPHER *cipher) {
   if (!hs->transcript.InitHash(version, cipher)) {
     return false;
   }

   // Initialize the secret to the zero key.
   hs->ResizeSecrets(hs->transcript.DigestLen());
   OPENSSL_memset(hs->secret().data(), 0, hs->secret().size());

   return true;
 }

 static bool hkdf_extract_to_secret(SSL_HANDSHAKE *hs, Span<const uint8_t> in) {
   size_t len;
   if (!HKDF_extract(hs->secret().data(), &len, hs->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, 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, psk);
 }

 bool tls13_init_early_key_schedule(SSL_HANDSHAKE *hs, Span<const uint8_t> psk) {
   SSL *const ssl = hs->ssl;
   return init_key_schedule(hs, ssl_session_protocol_version(ssl->session.get()),
                            ssl->session->cipher) &&
          hkdf_extract_to_secret(hs, psk);
 }

 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, in);
 }

 // derive_secret derives a secret of length |out.size()| and writes the result
 // in |out| with the given label, the current base secret, and the most
 // recently-saved handshake context. It returns true on success and false on
 // error.
 static bool derive_secret(SSL_HANDSHAKE *hs, Span<uint8_t> out,
                           Span<const char> label) {
   uint8_t context_hash[EVP_MAX_MD_SIZE];
   size_t context_hash_len;
   if (!hs->transcript.GetHash(context_hash, &context_hash_len)) {
     return false;
   }

   return hkdf_expand_label(out, hs->transcript.Digest(), hs->secret(), label,
                            MakeConstSpan(context_hash, context_hash_len));
 }

 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;
   if (!derive_secret(hs, hs->early_traffic_secret(),
                      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->master_key_length = hs->transcript.DigestLen();
   return derive_secret(
       hs,
       MakeSpan(hs->new_session->master_key, hs->new_session->master_key_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_key = MakeSpan(session->master_key, session->master_key_length);
   return hkdf_expand_label(session_key, digest, session_key,
                            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, uint16_t version,
                              const EVP_MD *digest, Span<const uint8_t> psk,
                              Span<const uint8_t> context) {
   uint8_t binder_context[EVP_MAX_MD_SIZE];
   unsigned binder_context_len;
   if (!EVP_Digest(NULL, 0, binder_context, &binder_context_len, digest, NULL)) {
     return false;
   }

   uint8_t early_secret[EVP_MAX_MD_SIZE] = {0};
   size_t early_secret_len;
   if (!HKDF_extract(early_secret, &early_secret_len, digest, psk.data(),
                     psk.size(), NULL, 0)) {
     return false;
   }

   uint8_t binder_key_buf[EVP_MAX_MD_SIZE] = {0};
   auto binder_key = MakeSpan(binder_key_buf, EVP_MD_size(digest));
   if (!hkdf_expand_label(binder_key, digest,
                          MakeConstSpan(early_secret, early_secret_len),
                          label_to_span(kTLS13LabelPSKBinder),
                          MakeConstSpan(binder_context, binder_context_len)) ||
       !tls13_verify_data(out, out_len, digest, version, binder_key, context)) {
     return false;
   }

   assert(*out_len == EVP_MD_size(digest));
   return true;
 }

 static bool hash_transcript_and_truncated_client_hello(
     SSL_HANDSHAKE *hs, uint8_t *out, size_t *out_len, const EVP_MD *digest,
     Span<const uint8_t> client_hello, size_t binders_len) {
   // Truncate the ClientHello.
   if (binders_len + 2 < binders_len || client_hello.size() < binders_len + 2) {
     return false;
   }
   client_hello = client_hello.subspan(0, client_hello.size() - binders_len - 2);

   ScopedEVP_MD_CTX ctx;
   unsigned len;
   if (!hs->transcript.CopyToHashContext(ctx.get(), digest) ||
       !EVP_DigestUpdate(ctx.get(), client_hello.data(), client_hello.size()) ||
       !EVP_DigestFinal_ex(ctx.get(), out, &len)) {
     return false;
   }

   *out_len = len;
   return true;
 }

 bool tls13_write_psk_binder(SSL_HANDSHAKE *hs, Span<uint8_t> msg) {
   SSL *const ssl = hs->ssl;
   const EVP_MD *digest = ssl_session_get_digest(ssl->session.get());
   size_t hash_len = EVP_MD_size(digest);

   ScopedEVP_MD_CTX ctx;
   uint8_t context[EVP_MAX_MD_SIZE];
   size_t context_len;
   uint8_t verify_data[EVP_MAX_MD_SIZE];
   size_t verify_data_len;
   if (!hash_transcript_and_truncated_client_hello(
           hs, context, &context_len, digest, msg,
           1 /* length prefix */ + hash_len) ||
       !tls13_psk_binder(verify_data, &verify_data_len,
                         ssl->session->ssl_version, digest,
                         MakeConstSpan(ssl->session->master_key,
                                       ssl->session->master_key_length),
                         MakeConstSpan(context, context_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);
   return true;
 }

 bool tls13_verify_psk_binder(SSL_HANDSHAKE *hs, SSL_SESSION *session,
                              const SSLMessage &msg, CBS *binders) {
   uint8_t context[EVP_MAX_MD_SIZE];
   size_t context_len;
   uint8_t verify_data[EVP_MAX_MD_SIZE];
   size_t verify_data_len;
   CBS binder;
   if (!hash_transcript_and_truncated_client_hello(hs, context, &context_len,
                                                   hs->transcript.Digest(),
                                                   msg.raw, CBS_len(binders)) ||
       !tls13_psk_binder(
           verify_data, &verify_data_len, hs->ssl->version,
           hs->transcript.Digest(),
           MakeConstSpan(session->master_key, session->master_key_length),
           MakeConstSpan(context, context_len)) ||
       // 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;
 }

 BSSL_NAMESPACE_END
	/* 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, uint16_t version,
	const SSL_CIPHER *cipher) {
	if (!hs->transcript.InitHash(version, cipher)) {
	return false;
	}

	// Initialize the secret to the zero key.
	hs->ResizeSecrets(hs->transcript.DigestLen());
	OPENSSL_memset(hs->secret().data(), 0, hs->secret().size());

	return true;
	}

	static bool hkdf_extract_to_secret(SSL_HANDSHAKE *hs, Span<const uint8_t> in) {
	size_t len;
	if (!HKDF_extract(hs->secret().data(), &len, hs->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, 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, psk);
	}

	bool tls13_init_early_key_schedule(SSL_HANDSHAKE *hs, Span<const uint8_t> psk) {
	SSL *const ssl = hs->ssl;
	return init_key_schedule(hs, ssl_session_protocol_version(ssl->session.get()),
	ssl->session->cipher) &&
	hkdf_extract_to_secret(hs, psk);
	}

	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, in);
	}

	// derive_secret derives a secret of length \|out.size()\| and writes the result
	// in \|out\| with the given label, the current base secret, and the most
	// recently-saved handshake context. It returns true on success and false on
	// error.
	static bool derive_secret(SSL_HANDSHAKE *hs, Span<uint8_t> out,
	Span<const char> label) {
	uint8_t context_hash[EVP_MAX_MD_SIZE];
	size_t context_hash_len;
	if (!hs->transcript.GetHash(context_hash, &context_hash_len)) {
	return false;
	}

	return hkdf_expand_label(out, hs->transcript.Digest(), hs->secret(), label,
	MakeConstSpan(context_hash, context_hash_len));
	}

	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;
	if (!derive_secret(hs, hs->early_traffic_secret(),
	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->master_key_length = hs->transcript.DigestLen();
	return derive_secret(
	hs,
	MakeSpan(hs->new_session->master_key, hs->new_session->master_key_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_key = MakeSpan(session->master_key, session->master_key_length);
	return hkdf_expand_label(session_key, digest, session_key,
	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, uint16_t version,
	const EVP_MD *digest, Span<const uint8_t> psk,
	Span<const uint8_t> context) {
	uint8_t binder_context[EVP_MAX_MD_SIZE];
	unsigned binder_context_len;
	if (!EVP_Digest(NULL, 0, binder_context, &binder_context_len, digest, NULL)) {
	return false;
	}

	uint8_t early_secret[EVP_MAX_MD_SIZE] = {0};
	size_t early_secret_len;
	if (!HKDF_extract(early_secret, &early_secret_len, digest, psk.data(),
	psk.size(), NULL, 0)) {
	return false;
	}

	uint8_t binder_key_buf[EVP_MAX_MD_SIZE] = {0};
	auto binder_key = MakeSpan(binder_key_buf, EVP_MD_size(digest));
	if (!hkdf_expand_label(binder_key, digest,
	MakeConstSpan(early_secret, early_secret_len),
	label_to_span(kTLS13LabelPSKBinder),
	MakeConstSpan(binder_context, binder_context_len)) \|\|
	!tls13_verify_data(out, out_len, digest, version, binder_key, context)) {
	return false;
	}

	assert(*out_len == EVP_MD_size(digest));
	return true;
	}

	static bool hash_transcript_and_truncated_client_hello(
	SSL_HANDSHAKE hs, uint8_t out, size_t out_len, const EVP_MD digest,
	Span<const uint8_t> client_hello, size_t binders_len) {
	// Truncate the ClientHello.
	if (binders_len + 2 < binders_len \|\| client_hello.size() < binders_len + 2) {
	return false;
	}
	client_hello = client_hello.subspan(0, client_hello.size() - binders_len - 2);

	ScopedEVP_MD_CTX ctx;
	unsigned len;
	if (!hs->transcript.CopyToHashContext(ctx.get(), digest) \|\|
	!EVP_DigestUpdate(ctx.get(), client_hello.data(), client_hello.size()) \|\|
	!EVP_DigestFinal_ex(ctx.get(), out, &len)) {
	return false;
	}

	*out_len = len;
	return true;
	}

	bool tls13_write_psk_binder(SSL_HANDSHAKE *hs, Span<uint8_t> msg) {
	SSL *const ssl = hs->ssl;
	const EVP_MD *digest = ssl_session_get_digest(ssl->session.get());
	size_t hash_len = EVP_MD_size(digest);

	ScopedEVP_MD_CTX ctx;
	uint8_t context[EVP_MAX_MD_SIZE];
	size_t context_len;
	uint8_t verify_data[EVP_MAX_MD_SIZE];
	size_t verify_data_len;
	if (!hash_transcript_and_truncated_client_hello(
	hs, context, &context_len, digest, msg,
	1 /* length prefix */ + hash_len) \|\|
	!tls13_psk_binder(verify_data, &verify_data_len,
	ssl->session->ssl_version, digest,
	MakeConstSpan(ssl->session->master_key,
	ssl->session->master_key_length),
	MakeConstSpan(context, context_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);
	return true;
	}

	bool tls13_verify_psk_binder(SSL_HANDSHAKE hs, SSL_SESSION session,
	const SSLMessage &msg, CBS *binders) {
	uint8_t context[EVP_MAX_MD_SIZE];
	size_t context_len;
	uint8_t verify_data[EVP_MAX_MD_SIZE];
	size_t verify_data_len;
	CBS binder;
	if (!hash_transcript_and_truncated_client_hello(hs, context, &context_len,
	hs->transcript.Digest(),
	msg.raw, CBS_len(binders)) \|\|
	!tls13_psk_binder(
	verify_data, &verify_data_len, hs->ssl->version,
	hs->transcript.Digest(),
	MakeConstSpan(session->master_key, session->master_key_length),
	MakeConstSpan(context, context_len)) \|\|
	// 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;
	}

	BSSL_NAMESPACE_END