BoringSSL as optional cryptobackend for ngtcp2

PR добавляет возможность использовать BoringSSL в ngtcp2 в качестве криптобиблиотеки. Для проектов в Аркадии, уже зависящих от ngtcp2, добавлена явная зависимость от слоя абстракции quictls (сейчас в транке ngtcp2 собирается с quictls).
commit_hash:3d6607abecfcff2157859acbdd18f9d0345ac485

1 files changed, 1379 insertions, 0 deletions

diff --git a/contrib/restricted/google/boringssl/ssl/tls13_server.cc b/contrib/restricted/google/boringssl/ssl/tls13_server.cc
new file mode 100644
index 00000000000..32a29718fa0
--- /dev/null
+++ b/contrib/restricted/google/boringssl/ssl/tls13_server.cc
@@ -0,0 +1,1379 @@
+/* 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 <contrib/restricted/google/boringssl/include/openssl/ssl.h>
+
+#include <assert.h>
+#include <string.h>
+
+#include <algorithm>
+#include <tuple>
+
+#include <contrib/restricted/google/boringssl/include/openssl/aead.h>
+#include <contrib/restricted/google/boringssl/include/openssl/bytestring.h>
+#include <contrib/restricted/google/boringssl/include/openssl/digest.h>
+#include <contrib/restricted/google/boringssl/include/openssl/err.h>
+#include <contrib/restricted/google/boringssl/include/openssl/hpke.h>
+#include <contrib/restricted/google/boringssl/include/openssl/mem.h>
+#include <contrib/restricted/google/boringssl/include/openssl/rand.h>
+#include <contrib/restricted/google/boringssl/include/openssl/stack.h>
+
+#include "../crypto/internal.h"
+#include "internal.h"
+
+
+BSSL_NAMESPACE_BEGIN
+
+static const uint8_t kZeroes[EVP_MAX_MD_SIZE] = {0};
+
+// Allow a minute of ticket age skew in either direction. This covers
+// transmission delays in ClientHello and NewSessionTicket, as well as
+// drift between client and server clock rate since the ticket was issued.
+// See RFC 8446, section 8.3.
+static const int32_t kMaxTicketAgeSkewSeconds = 60;
+
+static bool resolve_ecdhe_secret(SSL_HANDSHAKE *hs,
+                                 const SSL_CLIENT_HELLO *client_hello) {
+  SSL *const ssl = hs->ssl;
+  const uint16_t group_id = hs->new_session->group_id;
+
+  bool found_key_share;
+  Span<const uint8_t> peer_key;
+  uint8_t alert = SSL_AD_DECODE_ERROR;
+  if (!ssl_ext_key_share_parse_clienthello(hs, &found_key_share, &peer_key,
+                                           &alert, client_hello)) {
+    ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
+    return false;
+  }
+
+  if (!found_key_share) {
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
+    OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_CURVE);
+    return false;
+  }
+
+  Array<uint8_t> secret;
+  SSL_HANDSHAKE_HINTS *const hints = hs->hints.get();
+  if (hints && !hs->hints_requested && hints->key_share_group_id == group_id &&
+      !hints->key_share_secret.empty()) {
+    // Copy the key_share secret from hints.
+    if (!hs->key_share_ciphertext.CopyFrom(hints->key_share_ciphertext) ||
+        !secret.CopyFrom(hints->key_share_secret)) {
+      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+      return false;
+    }
+  } else {
+    ScopedCBB ciphertext;
+    UniquePtr<SSLKeyShare> key_share = SSLKeyShare::Create(group_id);
+    if (!key_share ||  //
+        !CBB_init(ciphertext.get(), 32) ||
+        !key_share->Encap(ciphertext.get(), &secret, &alert, peer_key) ||
+        !CBBFinishArray(ciphertext.get(), &hs->key_share_ciphertext)) {
+      ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
+      return false;
+    }
+    if (hints && hs->hints_requested) {
+      hints->key_share_group_id = group_id;
+      if (!hints->key_share_ciphertext.CopyFrom(hs->key_share_ciphertext) ||
+          !hints->key_share_secret.CopyFrom(secret)) {
+        ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+        return false;
+      }
+    }
+  }
+
+  return tls13_advance_key_schedule(hs, secret);
+}
+
+static int ssl_ext_supported_versions_add_serverhello(SSL_HANDSHAKE *hs,
+                                                      CBB *out) {
+  CBB contents;
+  if (!CBB_add_u16(out, TLSEXT_TYPE_supported_versions) ||
+      !CBB_add_u16_length_prefixed(out, &contents) ||
+      !CBB_add_u16(&contents, hs->ssl->version) ||
+      !CBB_flush(out)) {
+    return 0;
+  }
+
+  return 1;
+}
+
+static const SSL_CIPHER *choose_tls13_cipher(
+    const SSL *ssl, const SSL_CLIENT_HELLO *client_hello) {
+  CBS cipher_suites;
+  CBS_init(&cipher_suites, client_hello->cipher_suites,
+           client_hello->cipher_suites_len);
+
+  const uint16_t version = ssl_protocol_version(ssl);
+
+  return ssl_choose_tls13_cipher(cipher_suites,
+                                 ssl->config->aes_hw_override
+                                     ? ssl->config->aes_hw_override_value
+                                     : EVP_has_aes_hardware(),
+                                 version, ssl->config->tls13_cipher_policy);
+}
+
+static bool add_new_session_tickets(SSL_HANDSHAKE *hs, bool *out_sent_tickets) {
+  SSL *const ssl = hs->ssl;
+  if (// If the client doesn't accept resumption with PSK_DHE_KE, don't send a
+      // session ticket.
+      !hs->accept_psk_mode ||
+      // We only implement stateless resumption in TLS 1.3, so skip sending
+      // tickets if disabled.
+      (SSL_get_options(ssl) & SSL_OP_NO_TICKET)) {
+    *out_sent_tickets = false;
+    return true;
+  }
+
+  // Rebase the session timestamp so that it is measured from ticket
+  // issuance.
+  ssl_session_rebase_time(ssl, hs->new_session.get());
+
+  assert(ssl->session_ctx->num_tickets <= kMaxTickets);
+  for (size_t i = 0; i < ssl->session_ctx->num_tickets; i++) {
+    UniquePtr<SSL_SESSION> session(
+        SSL_SESSION_dup(hs->new_session.get(), SSL_SESSION_INCLUDE_NONAUTH));
+    if (!session) {
+      return false;
+    }
+
+    if (!RAND_bytes((uint8_t *)&session->ticket_age_add, 4)) {
+      return false;
+    }
+    session->ticket_age_add_valid = true;
+    bool enable_early_data =
+        ssl->enable_early_data &&
+        (!ssl->quic_method || !ssl->config->quic_early_data_context.empty());
+    if (enable_early_data) {
+      // QUIC does not use the max_early_data_size parameter and always sets it
+      // to a fixed value. See RFC 9001, section 4.6.1.
+      session->ticket_max_early_data =
+          ssl->quic_method != nullptr ? 0xffffffff : kMaxEarlyDataAccepted;
+    }
+
+    static_assert(kMaxTickets < 256, "Too many tickets");
+    assert(i < 256);
+    uint8_t nonce[] = {static_cast<uint8_t>(i)};
+
+    ScopedCBB cbb;
+    CBB body, nonce_cbb, ticket, extensions;
+    if (!ssl->method->init_message(ssl, cbb.get(), &body,
+                                   SSL3_MT_NEW_SESSION_TICKET) ||
+        !CBB_add_u32(&body, session->timeout) ||
+        !CBB_add_u32(&body, session->ticket_age_add) ||
+        !CBB_add_u8_length_prefixed(&body, &nonce_cbb) ||
+        !CBB_add_bytes(&nonce_cbb, nonce, sizeof(nonce)) ||
+        !CBB_add_u16_length_prefixed(&body, &ticket) ||
+        !tls13_derive_session_psk(session.get(), nonce) ||
+        !ssl_encrypt_ticket(hs, &ticket, session.get()) ||
+        !CBB_add_u16_length_prefixed(&body, &extensions)) {
+      return false;
+    }
+
+    if (enable_early_data) {
+      CBB early_data;
+      if (!CBB_add_u16(&extensions, TLSEXT_TYPE_early_data) ||
+          !CBB_add_u16_length_prefixed(&extensions, &early_data) ||
+          !CBB_add_u32(&early_data, session->ticket_max_early_data) ||
+          !CBB_flush(&extensions)) {
+        return false;
+      }
+    }
+
+    // Add a fake extension. See RFC 8701.
+    if (!CBB_add_u16(&extensions,
+                     ssl_get_grease_value(hs, ssl_grease_ticket_extension)) ||
+        !CBB_add_u16(&extensions, 0 /* empty */)) {
+      return false;
+    }
+
+    if (!ssl_add_message_cbb(ssl, cbb.get())) {
+      return false;
+    }
+  }
+
+  *out_sent_tickets = true;
+  return true;
+}
+
+static bool check_credential(SSL_HANDSHAKE *hs, const SSL_CREDENTIAL *cred,
+                             uint16_t *out_sigalg) {
+  switch (cred->type) {
+    case SSLCredentialType::kX509:
+      break;
+    case SSLCredentialType::kDelegated:
+      // Check that the peer supports the signature over the delegated
+      // credential.
+      if (std::find(hs->peer_sigalgs.begin(), hs->peer_sigalgs.end(),
+                    cred->dc_algorithm) == hs->peer_sigalgs.end()) {
+        OPENSSL_PUT_ERROR(SSL, SSL_R_NO_COMMON_SIGNATURE_ALGORITHMS);
+        return false;
+      }
+      break;
+  }
+
+  // All currently supported credentials require a signature. If |cred| is a
+  // delegated credential, this also checks that the peer supports delegated
+  // credentials and matched |dc_cert_verify_algorithm|.
+  return tls1_choose_signature_algorithm(hs, cred, out_sigalg);
+}
+
+static enum ssl_hs_wait_t do_select_parameters(SSL_HANDSHAKE *hs) {
+  // At this point, most ClientHello extensions have already been processed by
+  // the common handshake logic. Resolve the remaining non-PSK parameters.
+  SSL *const ssl = hs->ssl;
+  SSLMessage msg;
+  SSL_CLIENT_HELLO client_hello;
+  if (!hs->GetClientHello(&msg, &client_hello)) {
+    return ssl_hs_error;
+  }
+
+  if (ssl->quic_method != nullptr && client_hello.session_id_len > 0) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_COMPATIBILITY_MODE);
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
+    return ssl_hs_error;
+  }
+  OPENSSL_memcpy(hs->session_id, client_hello.session_id,
+                 client_hello.session_id_len);
+  hs->session_id_len = client_hello.session_id_len;
+
+  Array<SSL_CREDENTIAL *> creds;
+  if (!ssl_get_credential_list(hs, &creds)) {
+    return ssl_hs_error;
+  }
+  if (creds.empty()) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_NO_CERTIFICATE_SET);
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+    return ssl_hs_error;
+  }
+
+  // Select the credential to use.
+  for (SSL_CREDENTIAL *cred : creds) {
+    ERR_clear_error();
+    uint16_t sigalg;
+    if (check_credential(hs, cred, &sigalg)) {
+      hs->credential = UpRef(cred);
+      hs->signature_algorithm = sigalg;
+      break;
+    }
+  }
+  if (hs->credential == nullptr) {
+    // The error from the last attempt is in the error queue.
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
+    return ssl_hs_error;
+  }
+
+  // Negotiate the cipher suite.
+  hs->new_cipher = choose_tls13_cipher(ssl, &client_hello);
+  if (hs->new_cipher == NULL) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_NO_SHARED_CIPHER);
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
+    return ssl_hs_error;
+  }
+
+  // HTTP/2 negotiation depends on the cipher suite, so ALPN negotiation was
+  // deferred. Complete it now.
+  uint8_t alert = SSL_AD_DECODE_ERROR;
+  if (!ssl_negotiate_alpn(hs, &alert, &client_hello)) {
+    ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
+    return ssl_hs_error;
+  }
+
+  // The PRF hash is now known.
+  if (!hs->transcript.InitHash(ssl_protocol_version(ssl), hs->new_cipher)) {
+    return ssl_hs_error;
+  }
+
+  hs->tls13_state = state13_select_session;
+  return ssl_hs_ok;
+}
+
+static enum ssl_ticket_aead_result_t select_session(
+    SSL_HANDSHAKE *hs, uint8_t *out_alert, UniquePtr<SSL_SESSION> *out_session,
+    int32_t *out_ticket_age_skew, bool *out_offered_ticket,
+    const SSLMessage &msg, const SSL_CLIENT_HELLO *client_hello) {
+  SSL *const ssl = hs->ssl;
+  *out_session = nullptr;
+
+  CBS pre_shared_key;
+  *out_offered_ticket = ssl_client_hello_get_extension(
+      client_hello, &pre_shared_key, TLSEXT_TYPE_pre_shared_key);
+  if (!*out_offered_ticket) {
+    return ssl_ticket_aead_ignore_ticket;
+  }
+
+  // Per RFC 8446, section 4.2.9, servers MUST abort the handshake if the client
+  // sends pre_shared_key without psk_key_exchange_modes.
+  CBS unused;
+  if (!ssl_client_hello_get_extension(client_hello, &unused,
+                                      TLSEXT_TYPE_psk_key_exchange_modes)) {
+    *out_alert = SSL_AD_MISSING_EXTENSION;
+    OPENSSL_PUT_ERROR(SSL, SSL_R_MISSING_EXTENSION);
+    return ssl_ticket_aead_error;
+  }
+
+  CBS ticket, binders;
+  uint32_t client_ticket_age;
+  if (!ssl_ext_pre_shared_key_parse_clienthello(
+          hs, &ticket, &binders, &client_ticket_age, out_alert, client_hello,
+          &pre_shared_key)) {
+    return ssl_ticket_aead_error;
+  }
+
+  // If the peer did not offer psk_dhe, ignore the resumption.
+  if (!hs->accept_psk_mode) {
+    return ssl_ticket_aead_ignore_ticket;
+  }
+
+  // TLS 1.3 session tickets are renewed separately as part of the
+  // NewSessionTicket.
+  bool unused_renew;
+  UniquePtr<SSL_SESSION> session;
+  enum ssl_ticket_aead_result_t ret =
+      ssl_process_ticket(hs, &session, &unused_renew, ticket, {});
+  switch (ret) {
+    case ssl_ticket_aead_success:
+      break;
+    case ssl_ticket_aead_error:
+      *out_alert = SSL_AD_INTERNAL_ERROR;
+      return ret;
+    default:
+      return ret;
+  }
+
+  if (!ssl_session_is_resumable(hs, session.get()) ||
+      // Historically, some TLS 1.3 tickets were missing ticket_age_add.
+      !session->ticket_age_add_valid) {
+    return ssl_ticket_aead_ignore_ticket;
+  }
+
+  // Recover the client ticket age and convert to seconds.
+  client_ticket_age -= session->ticket_age_add;
+  client_ticket_age /= 1000;
+
+  struct OPENSSL_timeval now;
+  ssl_get_current_time(ssl, &now);
+
+  // Compute the server ticket age in seconds.
+  assert(now.tv_sec >= session->time);
+  uint64_t server_ticket_age = now.tv_sec - session->time;
+
+  // To avoid overflowing |hs->ticket_age_skew|, we will not resume
+  // 68-year-old sessions.
+  if (server_ticket_age > INT32_MAX) {
+    return ssl_ticket_aead_ignore_ticket;
+  }
+
+  *out_ticket_age_skew = static_cast<int32_t>(client_ticket_age) -
+                         static_cast<int32_t>(server_ticket_age);
+
+  // Check the PSK binder.
+  if (!tls13_verify_psk_binder(hs, session.get(), msg, &binders)) {
+    *out_alert = SSL_AD_DECRYPT_ERROR;
+    return ssl_ticket_aead_error;
+  }
+
+  *out_session = std::move(session);
+  return ssl_ticket_aead_success;
+}
+
+static bool quic_ticket_compatible(const SSL_SESSION *session,
+                                   const SSL_CONFIG *config) {
+  if (!session->is_quic) {
+    return true;
+  }
+
+  if (session->quic_early_data_context.empty() ||
+      config->quic_early_data_context.size() !=
+          session->quic_early_data_context.size() ||
+      CRYPTO_memcmp(config->quic_early_data_context.data(),
+                    session->quic_early_data_context.data(),
+                    session->quic_early_data_context.size()) != 0) {
+    return false;
+  }
+  return true;
+}
+
+static enum ssl_hs_wait_t do_select_session(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  SSLMessage msg;
+  SSL_CLIENT_HELLO client_hello;
+  if (!hs->GetClientHello(&msg, &client_hello)) {
+    return ssl_hs_error;
+  }
+
+  uint8_t alert = SSL_AD_DECODE_ERROR;
+  UniquePtr<SSL_SESSION> session;
+  bool offered_ticket = false;
+  switch (select_session(hs, &alert, &session, &ssl->s3->ticket_age_skew,
+                         &offered_ticket, msg, &client_hello)) {
+    case ssl_ticket_aead_ignore_ticket:
+      assert(!session);
+      if (!ssl_get_new_session(hs)) {
+        ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+        return ssl_hs_error;
+      }
+      break;
+
+    case ssl_ticket_aead_success:
+      // Carry over authentication information from the previous handshake into
+      // a fresh session.
+      hs->new_session =
+          SSL_SESSION_dup(session.get(), SSL_SESSION_DUP_AUTH_ONLY);
+      if (hs->new_session == nullptr) {
+        ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+        return ssl_hs_error;
+      }
+
+      ssl->s3->session_reused = true;
+      hs->can_release_private_key = true;
+
+      // Resumption incorporates fresh key material, so refresh the timeout.
+      ssl_session_renew_timeout(ssl, hs->new_session.get(),
+                                ssl->session_ctx->session_psk_dhe_timeout);
+      break;
+
+    case ssl_ticket_aead_error:
+      ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
+      return ssl_hs_error;
+
+    case ssl_ticket_aead_retry:
+      hs->tls13_state = state13_select_session;
+      return ssl_hs_pending_ticket;
+  }
+
+  // Negotiate ALPS now, after ALPN is negotiated and |hs->new_session| is
+  // initialized.
+  if (!ssl_negotiate_alps(hs, &alert, &client_hello)) {
+    ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
+    return ssl_hs_error;
+  }
+
+  // Record connection properties in the new session.
+  hs->new_session->cipher = hs->new_cipher;
+  if (!tls1_get_shared_group(hs, &hs->new_session->group_id)) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_NO_SHARED_GROUP);
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
+    return ssl_hs_error;
+  }
+
+  // Determine if we need HelloRetryRequest.
+  bool found_key_share;
+  if (!ssl_ext_key_share_parse_clienthello(hs, &found_key_share,
+                                           /*out_key_share=*/nullptr, &alert,
+                                           &client_hello)) {
+    ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
+    return ssl_hs_error;
+  }
+
+  // Determine if we're negotiating 0-RTT.
+  if (!ssl->enable_early_data) {
+    ssl->s3->early_data_reason = ssl_early_data_disabled;
+  } else if (!offered_ticket) {
+    ssl->s3->early_data_reason = ssl_early_data_no_session_offered;
+  } else if (!session) {
+    ssl->s3->early_data_reason = ssl_early_data_session_not_resumed;
+  } else if (session->ticket_max_early_data == 0) {
+    ssl->s3->early_data_reason = ssl_early_data_unsupported_for_session;
+  } else if (!hs->early_data_offered) {
+    ssl->s3->early_data_reason = ssl_early_data_peer_declined;
+  } else if (hs->channel_id_negotiated) {
+    // Channel ID is incompatible with 0-RTT.
+    ssl->s3->early_data_reason = ssl_early_data_channel_id;
+  } else if (MakeConstSpan(ssl->s3->alpn_selected) != session->early_alpn) {
+    // The negotiated ALPN must match the one in the ticket.
+    ssl->s3->early_data_reason = ssl_early_data_alpn_mismatch;
+  } else if (hs->new_session->has_application_settings !=
+                 session->has_application_settings ||
+             MakeConstSpan(hs->new_session->local_application_settings) !=
+                 session->local_application_settings) {
+    ssl->s3->early_data_reason = ssl_early_data_alps_mismatch;
+  } else if (ssl->s3->ticket_age_skew < -kMaxTicketAgeSkewSeconds ||
+             kMaxTicketAgeSkewSeconds < ssl->s3->ticket_age_skew) {
+    ssl->s3->early_data_reason = ssl_early_data_ticket_age_skew;
+  } else if (!quic_ticket_compatible(session.get(), hs->config)) {
+    ssl->s3->early_data_reason = ssl_early_data_quic_parameter_mismatch;
+  } else if (!found_key_share) {
+    ssl->s3->early_data_reason = ssl_early_data_hello_retry_request;
+  } else {
+    // |ssl_session_is_resumable| forbids cross-cipher resumptions even if the
+    // PRF hashes match.
+    assert(hs->new_cipher == session->cipher);
+
+    ssl->s3->early_data_reason = ssl_early_data_accepted;
+    ssl->s3->early_data_accepted = true;
+  }
+
+  // Store the ALPN and ALPS values in the session for 0-RTT. Note the peer
+  // applications settings are not generally known until client
+  // EncryptedExtensions.
+  if (!hs->new_session->early_alpn.CopyFrom(ssl->s3->alpn_selected)) {
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+    return ssl_hs_error;
+  }
+
+  // The peer applications settings are usually received later, in
+  // EncryptedExtensions. But, in 0-RTT handshakes, we carry over the
+  // values from |session|. Do this now, before |session| is discarded.
+  if (ssl->s3->early_data_accepted &&
+      hs->new_session->has_application_settings &&
+      !hs->new_session->peer_application_settings.CopyFrom(
+          session->peer_application_settings)) {
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+    return ssl_hs_error;
+  }
+
+  // Copy the QUIC early data context to the session.
+  if (ssl->enable_early_data && ssl->quic_method) {
+    if (!hs->new_session->quic_early_data_context.CopyFrom(
+            hs->config->quic_early_data_context)) {
+      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+      return ssl_hs_error;
+    }
+  }
+
+  if (ssl->ctx->dos_protection_cb != NULL &&
+      ssl->ctx->dos_protection_cb(&client_hello) == 0) {
+    // Connection rejected for DOS reasons.
+    OPENSSL_PUT_ERROR(SSL, SSL_R_CONNECTION_REJECTED);
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+    return ssl_hs_error;
+  }
+
+  size_t hash_len = EVP_MD_size(
+      ssl_get_handshake_digest(ssl_protocol_version(ssl), hs->new_cipher));
+
+  // Set up the key schedule and incorporate the PSK into the running secret.
+  if (!tls13_init_key_schedule(
+          hs, ssl->s3->session_reused
+                  ? MakeConstSpan(hs->new_session->secret,
+                                  hs->new_session->secret_length)
+                  : MakeConstSpan(kZeroes, hash_len)) ||
+      !ssl_hash_message(hs, msg)) {
+    return ssl_hs_error;
+  }
+
+  if (ssl->s3->early_data_accepted) {
+    if (!tls13_derive_early_secret(hs)) {
+      return ssl_hs_error;
+    }
+  } else if (hs->early_data_offered) {
+    ssl->s3->skip_early_data = true;
+  }
+
+  if (!found_key_share) {
+    ssl->method->next_message(ssl);
+    if (!hs->transcript.UpdateForHelloRetryRequest()) {
+      return ssl_hs_error;
+    }
+    hs->tls13_state = state13_send_hello_retry_request;
+    return ssl_hs_ok;
+  }
+
+  if (!resolve_ecdhe_secret(hs, &client_hello)) {
+    return ssl_hs_error;
+  }
+
+  ssl->method->next_message(ssl);
+  hs->ech_client_hello_buf.Reset();
+  hs->tls13_state = state13_send_server_hello;
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_send_hello_retry_request(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  if (hs->hints_requested) {
+    return ssl_hs_hints_ready;
+  }
+
+  ScopedCBB cbb;
+  CBB body, session_id, extensions;
+  if (!ssl->method->init_message(ssl, cbb.get(), &body, SSL3_MT_SERVER_HELLO) ||
+      !CBB_add_u16(&body, TLS1_2_VERSION) ||
+      !CBB_add_bytes(&body, kHelloRetryRequest, SSL3_RANDOM_SIZE) ||
+      !CBB_add_u8_length_prefixed(&body, &session_id) ||
+      !CBB_add_bytes(&session_id, hs->session_id, hs->session_id_len) ||
+      !CBB_add_u16(&body, SSL_CIPHER_get_protocol_id(hs->new_cipher)) ||
+      !CBB_add_u8(&body, 0 /* no compression */) ||
+      !CBB_add_u16_length_prefixed(&body, &extensions) ||
+      !CBB_add_u16(&extensions, TLSEXT_TYPE_supported_versions) ||
+      !CBB_add_u16(&extensions, 2 /* length */) ||
+      !CBB_add_u16(&extensions, ssl->version) ||
+      !CBB_add_u16(&extensions, TLSEXT_TYPE_key_share) ||
+      !CBB_add_u16(&extensions, 2 /* length */) ||
+      !CBB_add_u16(&extensions, hs->new_session->group_id)) {
+    return ssl_hs_error;
+  }
+  if (hs->ech_is_inner) {
+    // Fill a placeholder for the ECH confirmation value.
+    if (!CBB_add_u16(&extensions, TLSEXT_TYPE_encrypted_client_hello) ||
+        !CBB_add_u16(&extensions, ECH_CONFIRMATION_SIGNAL_LEN) ||
+        !CBB_add_zeros(&extensions, ECH_CONFIRMATION_SIGNAL_LEN)) {
+      return ssl_hs_error;
+    }
+  }
+  Array<uint8_t> hrr;
+  if (!ssl->method->finish_message(ssl, cbb.get(), &hrr)) {
+    return ssl_hs_error;
+  }
+  if (hs->ech_is_inner) {
+    // Now that the message is encoded, fill in the whole value.
+    size_t offset = hrr.size() - ECH_CONFIRMATION_SIGNAL_LEN;
+    if (!ssl_ech_accept_confirmation(
+            hs, MakeSpan(hrr).last(ECH_CONFIRMATION_SIGNAL_LEN),
+            ssl->s3->client_random, hs->transcript, /*is_hrr=*/true, hrr,
+            offset)) {
+      return ssl_hs_error;
+    }
+  }
+
+  if (!ssl->method->add_message(ssl, std::move(hrr)) ||
+      !ssl->method->add_change_cipher_spec(ssl)) {
+    return ssl_hs_error;
+  }
+
+  ssl->s3->used_hello_retry_request = true;
+  hs->tls13_state = state13_read_second_client_hello;
+  return ssl_hs_flush;
+}
+
+static enum ssl_hs_wait_t do_read_second_client_hello(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  SSLMessage msg;
+  if (!ssl->method->get_message(ssl, &msg)) {
+    return ssl_hs_read_message;
+  }
+  if (!ssl_check_message_type(ssl, msg, SSL3_MT_CLIENT_HELLO)) {
+    return ssl_hs_error;
+  }
+  SSL_CLIENT_HELLO client_hello;
+  if (!ssl_client_hello_init(ssl, &client_hello, msg.body)) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_CLIENTHELLO_PARSE_FAILED);
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+    return ssl_hs_error;
+  }
+
+  if (ssl->s3->ech_status == ssl_ech_accepted) {
+    // If we previously accepted the ClientHelloInner, the second ClientHello
+    // must contain an outer encrypted_client_hello extension.
+    CBS ech_body;
+    if (!ssl_client_hello_get_extension(&client_hello, &ech_body,
+                                        TLSEXT_TYPE_encrypted_client_hello)) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_MISSING_EXTENSION);
+      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_MISSING_EXTENSION);
+      return ssl_hs_error;
+    }
+    uint16_t kdf_id, aead_id;
+    uint8_t type, config_id;
+    CBS enc, payload;
+    if (!CBS_get_u8(&ech_body, &type) ||     //
+        type != ECH_CLIENT_OUTER ||          //
+        !CBS_get_u16(&ech_body, &kdf_id) ||  //
+        !CBS_get_u16(&ech_body, &aead_id) ||
+        !CBS_get_u8(&ech_body, &config_id) ||
+        !CBS_get_u16_length_prefixed(&ech_body, &enc) ||
+        !CBS_get_u16_length_prefixed(&ech_body, &payload) ||
+        CBS_len(&ech_body) != 0) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
+      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+      return ssl_hs_error;
+    }
+
+    if (kdf_id != EVP_HPKE_KDF_id(EVP_HPKE_CTX_kdf(hs->ech_hpke_ctx.get())) ||
+        aead_id !=
+            EVP_HPKE_AEAD_id(EVP_HPKE_CTX_aead(hs->ech_hpke_ctx.get())) ||
+        config_id != hs->ech_config_id || CBS_len(&enc) > 0) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
+      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
+      return ssl_hs_error;
+    }
+
+    // Decrypt the payload with the HPKE context from the first ClientHello.
+    uint8_t alert = SSL_AD_DECODE_ERROR;
+    bool unused;
+    if (!ssl_client_hello_decrypt(hs, &alert, &unused,
+                                  &hs->ech_client_hello_buf, &client_hello,
+                                  payload)) {
+      // Decryption failure is fatal in the second ClientHello.
+      OPENSSL_PUT_ERROR(SSL, SSL_R_DECRYPTION_FAILED);
+      ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
+      return ssl_hs_error;
+    }
+
+    // Reparse |client_hello| from the buffer owned by |hs|.
+    if (!hs->GetClientHello(&msg, &client_hello)) {
+      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+      return ssl_hs_error;
+    }
+  }
+
+  // We perform all our negotiation based on the first ClientHello (for
+  // consistency with what |select_certificate_cb| observed), which is in the
+  // transcript, so we can ignore most of this second one.
+  //
+  // We do, however, check the second PSK binder. This covers the client key
+  // share, in case we ever send half-RTT data (we currently do not). It is also
+  // a tricky computation, so we enforce the peer handled it correctly.
+  if (ssl->s3->session_reused) {
+    CBS pre_shared_key;
+    if (!ssl_client_hello_get_extension(&client_hello, &pre_shared_key,
+                                        TLSEXT_TYPE_pre_shared_key)) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_INCONSISTENT_CLIENT_HELLO);
+      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
+      return ssl_hs_error;
+    }
+
+    CBS ticket, binders;
+    uint32_t client_ticket_age;
+    uint8_t alert = SSL_AD_DECODE_ERROR;
+    if (!ssl_ext_pre_shared_key_parse_clienthello(
+            hs, &ticket, &binders, &client_ticket_age, &alert, &client_hello,
+            &pre_shared_key)) {
+      ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
+      return ssl_hs_error;
+    }
+
+    // Note it is important that we do not obtain a new |SSL_SESSION| from
+    // |ticket|. We have already selected parameters based on the first
+    // ClientHello (in the transcript) and must not switch partway through.
+    if (!tls13_verify_psk_binder(hs, hs->new_session.get(), msg, &binders)) {
+      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECRYPT_ERROR);
+      return ssl_hs_error;
+    }
+  }
+
+  if (!resolve_ecdhe_secret(hs, &client_hello)) {
+    return ssl_hs_error;
+  }
+
+  if (!ssl_hash_message(hs, msg)) {
+    return ssl_hs_error;
+  }
+
+  // ClientHello should be the end of the flight.
+  if (ssl->method->has_unprocessed_handshake_data(ssl)) {
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_UNEXPECTED_MESSAGE);
+    OPENSSL_PUT_ERROR(SSL, SSL_R_EXCESS_HANDSHAKE_DATA);
+    return ssl_hs_error;
+  }
+
+  ssl->method->next_message(ssl);
+  hs->ech_client_hello_buf.Reset();
+  hs->tls13_state = state13_send_server_hello;
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_send_server_hello(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+
+  Span<uint8_t> random(ssl->s3->server_random);
+
+  SSL_HANDSHAKE_HINTS *const hints = hs->hints.get();
+  if (hints && !hs->hints_requested &&
+      hints->server_random_tls13.size() == random.size()) {
+    OPENSSL_memcpy(random.data(), hints->server_random_tls13.data(),
+                   random.size());
+  } else {
+    RAND_bytes(random.data(), random.size());
+    if (hints && hs->hints_requested &&
+        !hints->server_random_tls13.CopyFrom(random)) {
+      return ssl_hs_error;
+    }
+  }
+
+  Array<uint8_t> server_hello;
+  ScopedCBB cbb;
+  CBB body, extensions, session_id;
+  if (!ssl->method->init_message(ssl, cbb.get(), &body, SSL3_MT_SERVER_HELLO) ||
+      !CBB_add_u16(&body, TLS1_2_VERSION) ||
+      !CBB_add_bytes(&body, ssl->s3->server_random,
+                     sizeof(ssl->s3->server_random)) ||
+      !CBB_add_u8_length_prefixed(&body, &session_id) ||
+      !CBB_add_bytes(&session_id, hs->session_id, hs->session_id_len) ||
+      !CBB_add_u16(&body, SSL_CIPHER_get_protocol_id(hs->new_cipher)) ||
+      !CBB_add_u8(&body, 0) ||
+      !CBB_add_u16_length_prefixed(&body, &extensions) ||
+      !ssl_ext_pre_shared_key_add_serverhello(hs, &extensions) ||
+      !ssl_ext_key_share_add_serverhello(hs, &extensions) ||
+      !ssl_ext_supported_versions_add_serverhello(hs, &extensions) ||
+      !ssl->method->finish_message(ssl, cbb.get(), &server_hello)) {
+    return ssl_hs_error;
+  }
+
+  assert(ssl->s3->ech_status != ssl_ech_accepted || hs->ech_is_inner);
+  if (hs->ech_is_inner) {
+    // Fill in the ECH confirmation signal.
+    const size_t offset = ssl_ech_confirmation_signal_hello_offset(ssl);
+    Span<uint8_t> random_suffix = random.last(ECH_CONFIRMATION_SIGNAL_LEN);
+    if (!ssl_ech_accept_confirmation(hs, random_suffix, ssl->s3->client_random,
+                                     hs->transcript,
+                                     /*is_hrr=*/false, server_hello, offset)) {
+      return ssl_hs_error;
+    }
+
+    // Update |server_hello|.
+    Span<uint8_t> server_hello_out =
+        MakeSpan(server_hello).subspan(offset, ECH_CONFIRMATION_SIGNAL_LEN);
+    OPENSSL_memcpy(server_hello_out.data(), random_suffix.data(),
+                   ECH_CONFIRMATION_SIGNAL_LEN);
+  }
+
+  if (!ssl->method->add_message(ssl, std::move(server_hello))) {
+    return ssl_hs_error;
+  }
+
+  hs->key_share_ciphertext.Reset();  // No longer needed.
+  if (!ssl->s3->used_hello_retry_request &&
+      !ssl->method->add_change_cipher_spec(ssl)) {
+    return ssl_hs_error;
+  }
+
+  // Derive and enable the handshake traffic secrets.
+  if (!tls13_derive_handshake_secrets(hs) ||
+      !tls13_set_traffic_key(ssl, ssl_encryption_handshake, evp_aead_seal,
+                             hs->new_session.get(),
+                             hs->server_handshake_secret())) {
+    return ssl_hs_error;
+  }
+
+  // Send EncryptedExtensions.
+  if (!ssl->method->init_message(ssl, cbb.get(), &body,
+                                 SSL3_MT_ENCRYPTED_EXTENSIONS) ||
+      !ssl_add_serverhello_tlsext(hs, &body) ||
+      !ssl_add_message_cbb(ssl, cbb.get())) {
+    return ssl_hs_error;
+  }
+
+  if (!ssl->s3->session_reused) {
+    // Determine whether to request a client certificate.
+    hs->cert_request = !!(hs->config->verify_mode & SSL_VERIFY_PEER);
+    // Only request a certificate if Channel ID isn't negotiated.
+    if ((hs->config->verify_mode & SSL_VERIFY_PEER_IF_NO_OBC) &&
+        hs->channel_id_negotiated) {
+      hs->cert_request = false;
+    }
+  }
+
+  // Send a CertificateRequest, if necessary.
+  if (hs->cert_request) {
+    CBB cert_request_extensions, sigalg_contents, sigalgs_cbb;
+    if (!ssl->method->init_message(ssl, cbb.get(), &body,
+                                   SSL3_MT_CERTIFICATE_REQUEST) ||
+        !CBB_add_u8(&body, 0 /* no certificate_request_context. */) ||
+        !CBB_add_u16_length_prefixed(&body, &cert_request_extensions) ||
+        !CBB_add_u16(&cert_request_extensions,
+                     TLSEXT_TYPE_signature_algorithms) ||
+        !CBB_add_u16_length_prefixed(&cert_request_extensions,
+                                     &sigalg_contents) ||
+        !CBB_add_u16_length_prefixed(&sigalg_contents, &sigalgs_cbb) ||
+        !tls12_add_verify_sigalgs(hs, &sigalgs_cbb)) {
+      return ssl_hs_error;
+    }
+
+    if (ssl_has_client_CAs(hs->config)) {
+      CBB ca_contents;
+      if (!CBB_add_u16(&cert_request_extensions,
+                       TLSEXT_TYPE_certificate_authorities) ||
+          !CBB_add_u16_length_prefixed(&cert_request_extensions,
+                                       &ca_contents) ||
+          !ssl_add_client_CA_list(hs, &ca_contents) ||
+          !CBB_flush(&cert_request_extensions)) {
+        return ssl_hs_error;
+      }
+    }
+
+    if (!ssl_add_message_cbb(ssl, cbb.get())) {
+      return ssl_hs_error;
+    }
+  }
+
+  // Send the server Certificate message, if necessary.
+  if (!ssl->s3->session_reused) {
+    if (!tls13_add_certificate(hs)) {
+      return ssl_hs_error;
+    }
+
+    hs->tls13_state = state13_send_server_certificate_verify;
+    return ssl_hs_ok;
+  }
+
+  hs->tls13_state = state13_send_server_finished;
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_send_server_certificate_verify(SSL_HANDSHAKE *hs) {
+  switch (tls13_add_certificate_verify(hs)) {
+    case ssl_private_key_success:
+      hs->tls13_state = state13_send_server_finished;
+      return ssl_hs_ok;
+
+    case ssl_private_key_retry:
+      hs->tls13_state = state13_send_server_certificate_verify;
+      return ssl_hs_private_key_operation;
+
+    case ssl_private_key_failure:
+      return ssl_hs_error;
+  }
+
+  assert(0);
+  return ssl_hs_error;
+}
+
+static enum ssl_hs_wait_t do_send_server_finished(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  if (hs->hints_requested) {
+    return ssl_hs_hints_ready;
+  }
+
+  hs->can_release_private_key = true;
+  if (!tls13_add_finished(hs) ||
+      // Update the secret to the master secret and derive traffic keys.
+      !tls13_advance_key_schedule(
+          hs, MakeConstSpan(kZeroes, hs->transcript.DigestLen())) ||
+      !tls13_derive_application_secrets(hs) ||
+      !tls13_set_traffic_key(ssl, ssl_encryption_application, evp_aead_seal,
+                             hs->new_session.get(),
+                             hs->server_traffic_secret_0())) {
+    return ssl_hs_error;
+  }
+
+  hs->tls13_state = state13_send_half_rtt_ticket;
+  return hs->handback ? ssl_hs_handback : ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_send_half_rtt_ticket(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+
+  if (ssl->s3->early_data_accepted) {
+    // If accepting 0-RTT, we send tickets half-RTT. This gets the tickets on
+    // the wire sooner and also avoids triggering a write on |SSL_read| when
+    // processing the client Finished. This requires computing the client
+    // Finished early. See RFC 8446, section 4.6.1.
+    static const uint8_t kEndOfEarlyData[4] = {SSL3_MT_END_OF_EARLY_DATA, 0,
+                                               0, 0};
+    if (ssl->quic_method == nullptr &&
+        !hs->transcript.Update(kEndOfEarlyData)) {
+      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+      return ssl_hs_error;
+    }
+
+    size_t finished_len;
+    if (!tls13_finished_mac(hs, hs->expected_client_finished().data(),
+                            &finished_len, false /* client */)) {
+      return ssl_hs_error;
+    }
+
+    if (finished_len != hs->expected_client_finished().size()) {
+      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+      return ssl_hs_error;
+    }
+
+    // Feed the predicted Finished into the transcript. This allows us to derive
+    // the resumption secret early and send half-RTT tickets.
+    //
+    // TODO(davidben): This will need to be updated for DTLS 1.3.
+    assert(!SSL_is_dtls(hs->ssl));
+    assert(hs->expected_client_finished().size() <= 0xff);
+    uint8_t header[4] = {
+        SSL3_MT_FINISHED, 0, 0,
+        static_cast<uint8_t>(hs->expected_client_finished().size())};
+    bool unused_sent_tickets;
+    if (!hs->transcript.Update(header) ||
+        !hs->transcript.Update(hs->expected_client_finished()) ||
+        !tls13_derive_resumption_secret(hs) ||
+        !add_new_session_tickets(hs, &unused_sent_tickets)) {
+      return ssl_hs_error;
+    }
+  }
+
+  hs->tls13_state = state13_read_second_client_flight;
+  return ssl_hs_flush;
+}
+
+static enum ssl_hs_wait_t do_read_second_client_flight(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  if (ssl->s3->early_data_accepted) {
+    if (!tls13_set_traffic_key(ssl, ssl_encryption_early_data, evp_aead_open,
+                               hs->new_session.get(),
+                               hs->early_traffic_secret())) {
+      return ssl_hs_error;
+    }
+    hs->can_early_write = true;
+    hs->can_early_read = true;
+    hs->in_early_data = true;
+  }
+
+  // QUIC doesn't use an EndOfEarlyData message (RFC 9001, section 8.3), so we
+  // switch to client_handshake_secret before the early return.
+  if (ssl->quic_method != nullptr) {
+    if (!tls13_set_traffic_key(ssl, ssl_encryption_handshake, evp_aead_open,
+                               hs->new_session.get(),
+                               hs->client_handshake_secret())) {
+      return ssl_hs_error;
+    }
+    hs->tls13_state = state13_process_end_of_early_data;
+    return ssl->s3->early_data_accepted ? ssl_hs_early_return : ssl_hs_ok;
+  }
+
+  hs->tls13_state = state13_process_end_of_early_data;
+  return ssl->s3->early_data_accepted ? ssl_hs_read_end_of_early_data
+                                      : ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_process_end_of_early_data(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  // In protocols that use EndOfEarlyData, we must consume the extra message and
+  // switch to client_handshake_secret after the early return.
+  if (ssl->quic_method == nullptr) {
+    // If early data was not accepted, the EndOfEarlyData will be in the
+    // discarded early data.
+    if (hs->ssl->s3->early_data_accepted) {
+      SSLMessage msg;
+      if (!ssl->method->get_message(ssl, &msg)) {
+        return ssl_hs_read_message;
+      }
+      if (!ssl_check_message_type(ssl, msg, SSL3_MT_END_OF_EARLY_DATA)) {
+        return ssl_hs_error;
+      }
+      if (CBS_len(&msg.body) != 0) {
+        ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+        OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
+        return ssl_hs_error;
+      }
+      ssl->method->next_message(ssl);
+    }
+    if (!tls13_set_traffic_key(ssl, ssl_encryption_handshake, evp_aead_open,
+                               hs->new_session.get(),
+                               hs->client_handshake_secret())) {
+      return ssl_hs_error;
+    }
+  }
+  hs->tls13_state = state13_read_client_encrypted_extensions;
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_read_client_encrypted_extensions(
+    SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  // For now, only one extension uses client EncryptedExtensions. This function
+  // may be generalized if others use it in the future.
+  if (hs->new_session->has_application_settings &&
+      !ssl->s3->early_data_accepted) {
+    SSLMessage msg;
+    if (!ssl->method->get_message(ssl, &msg)) {
+      return ssl_hs_read_message;
+    }
+    if (!ssl_check_message_type(ssl, msg, SSL3_MT_ENCRYPTED_EXTENSIONS)) {
+      return ssl_hs_error;
+    }
+
+    CBS body = msg.body, extensions;
+    if (!CBS_get_u16_length_prefixed(&body, &extensions) ||
+        CBS_len(&body) != 0) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
+      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+      return ssl_hs_error;
+    }
+
+    uint16_t extension_type = TLSEXT_TYPE_application_settings_old;
+    if (hs->config->alps_use_new_codepoint) {
+      extension_type = TLSEXT_TYPE_application_settings;
+    }
+    SSLExtension application_settings(extension_type);
+    uint8_t alert = SSL_AD_DECODE_ERROR;
+    if (!ssl_parse_extensions(&extensions, &alert, {&application_settings},
+                              /*ignore_unknown=*/false)) {
+      ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
+      return ssl_hs_error;
+    }
+
+    if (!application_settings.present) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_MISSING_EXTENSION);
+      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_MISSING_EXTENSION);
+      return ssl_hs_error;
+    }
+
+    // Note that, if 0-RTT was accepted, these values will already have been
+    // initialized earlier.
+    if (!hs->new_session->peer_application_settings.CopyFrom(
+            application_settings.data) ||
+        !ssl_hash_message(hs, msg)) {
+      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+      return ssl_hs_error;
+    }
+
+    ssl->method->next_message(ssl);
+  }
+
+  hs->tls13_state = state13_read_client_certificate;
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_read_client_certificate(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  if (!hs->cert_request) {
+    if (!ssl->s3->session_reused) {
+      // OpenSSL returns X509_V_OK when no certificates are requested. This is
+      // classed by them as a bug, but it's assumed by at least NGINX. (Only do
+      // this in full handshakes as resumptions should carry over the previous
+      // |verify_result|, though this is a no-op because servers do not
+      // implement the client's odd soft-fail mode.)
+      hs->new_session->verify_result = X509_V_OK;
+    }
+
+    // Skip this state.
+    hs->tls13_state = state13_read_channel_id;
+    return ssl_hs_ok;
+  }
+
+  const bool allow_anonymous =
+      (hs->config->verify_mode & SSL_VERIFY_FAIL_IF_NO_PEER_CERT) == 0;
+  SSLMessage msg;
+  if (!ssl->method->get_message(ssl, &msg)) {
+    return ssl_hs_read_message;
+  }
+  if (!ssl_check_message_type(ssl, msg, SSL3_MT_CERTIFICATE) ||
+      !tls13_process_certificate(hs, msg, allow_anonymous) ||
+      !ssl_hash_message(hs, msg)) {
+    return ssl_hs_error;
+  }
+
+  ssl->method->next_message(ssl);
+  hs->tls13_state = state13_read_client_certificate_verify;
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_read_client_certificate_verify(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  if (sk_CRYPTO_BUFFER_num(hs->new_session->certs.get()) == 0) {
+    // Skip this state.
+    hs->tls13_state = state13_read_channel_id;
+    return ssl_hs_ok;
+  }
+
+  SSLMessage msg;
+  if (!ssl->method->get_message(ssl, &msg)) {
+    return ssl_hs_read_message;
+  }
+
+  switch (ssl_verify_peer_cert(hs)) {
+    case ssl_verify_ok:
+      break;
+    case ssl_verify_invalid:
+      return ssl_hs_error;
+    case ssl_verify_retry:
+      hs->tls13_state = state13_read_client_certificate_verify;
+      return ssl_hs_certificate_verify;
+  }
+
+  if (!ssl_check_message_type(ssl, msg, SSL3_MT_CERTIFICATE_VERIFY) ||
+      !tls13_process_certificate_verify(hs, msg) ||
+      !ssl_hash_message(hs, msg)) {
+    return ssl_hs_error;
+  }
+
+  ssl->method->next_message(ssl);
+  hs->tls13_state = state13_read_channel_id;
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_read_channel_id(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  if (!hs->channel_id_negotiated) {
+    hs->tls13_state = state13_read_client_finished;
+    return ssl_hs_ok;
+  }
+
+  SSLMessage msg;
+  if (!ssl->method->get_message(ssl, &msg)) {
+    return ssl_hs_read_message;
+  }
+  if (!ssl_check_message_type(ssl, msg, SSL3_MT_CHANNEL_ID) ||
+      !tls1_verify_channel_id(hs, msg) ||
+      !ssl_hash_message(hs, msg)) {
+    return ssl_hs_error;
+  }
+
+  ssl->method->next_message(ssl);
+  hs->tls13_state = state13_read_client_finished;
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_read_client_finished(SSL_HANDSHAKE *hs) {
+  SSL *const ssl = hs->ssl;
+  SSLMessage msg;
+  if (!ssl->method->get_message(ssl, &msg)) {
+    return ssl_hs_read_message;
+  }
+  if (!ssl_check_message_type(ssl, msg, SSL3_MT_FINISHED) ||
+      // If early data was accepted, we've already computed the client Finished
+      // and derived the resumption secret.
+      !tls13_process_finished(hs, msg, ssl->s3->early_data_accepted) ||
+      // evp_aead_seal keys have already been switched.
+      !tls13_set_traffic_key(ssl, ssl_encryption_application, evp_aead_open,
+                             hs->new_session.get(),
+                             hs->client_traffic_secret_0())) {
+    return ssl_hs_error;
+  }
+
+  if (!ssl->s3->early_data_accepted) {
+    if (!ssl_hash_message(hs, msg) ||
+        !tls13_derive_resumption_secret(hs)) {
+      return ssl_hs_error;
+    }
+
+    // We send post-handshake tickets as part of the handshake in 1-RTT.
+    hs->tls13_state = state13_send_new_session_ticket;
+  } else {
+    // We already sent half-RTT tickets.
+    hs->tls13_state = state13_done;
+  }
+
+  ssl->method->next_message(ssl);
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_send_new_session_ticket(SSL_HANDSHAKE *hs) {
+  bool sent_tickets;
+  if (!add_new_session_tickets(hs, &sent_tickets)) {
+    return ssl_hs_error;
+  }
+
+  hs->tls13_state = state13_done;
+  // In TLS 1.3, the NewSessionTicket isn't flushed until the server performs a
+  // write, to prevent a non-reading client from causing the server to hang in
+  // the case of a small server write buffer. Consumers which don't write data
+  // to the client will need to do a zero-byte write if they wish to flush the
+  // tickets.
+  if (hs->ssl->quic_method != nullptr && sent_tickets) {
+    return ssl_hs_flush;
+  }
+  return ssl_hs_ok;
+}
+
+enum ssl_hs_wait_t tls13_server_handshake(SSL_HANDSHAKE *hs) {
+  while (hs->tls13_state != state13_done) {
+    enum ssl_hs_wait_t ret = ssl_hs_error;
+    enum tls13_server_hs_state_t state =
+        static_cast<enum tls13_server_hs_state_t>(hs->tls13_state);
+    switch (state) {
+      case state13_select_parameters:
+        ret = do_select_parameters(hs);
+        break;
+      case state13_select_session:
+        ret = do_select_session(hs);
+        break;
+      case state13_send_hello_retry_request:
+        ret = do_send_hello_retry_request(hs);
+        break;
+      case state13_read_second_client_hello:
+        ret = do_read_second_client_hello(hs);
+        break;
+      case state13_send_server_hello:
+        ret = do_send_server_hello(hs);
+        break;
+      case state13_send_server_certificate_verify:
+        ret = do_send_server_certificate_verify(hs);
+        break;
+      case state13_send_server_finished:
+        ret = do_send_server_finished(hs);
+        break;
+      case state13_send_half_rtt_ticket:
+        ret = do_send_half_rtt_ticket(hs);
+        break;
+      case state13_read_second_client_flight:
+        ret = do_read_second_client_flight(hs);
+        break;
+      case state13_process_end_of_early_data:
+        ret = do_process_end_of_early_data(hs);
+        break;
+      case state13_read_client_encrypted_extensions:
+        ret = do_read_client_encrypted_extensions(hs);
+        break;
+      case state13_read_client_certificate:
+        ret = do_read_client_certificate(hs);
+        break;
+      case state13_read_client_certificate_verify:
+        ret = do_read_client_certificate_verify(hs);
+        break;
+      case state13_read_channel_id:
+        ret = do_read_channel_id(hs);
+        break;
+      case state13_read_client_finished:
+        ret = do_read_client_finished(hs);
+        break;
+      case state13_send_new_session_ticket:
+        ret = do_send_new_session_ticket(hs);
+        break;
+      case state13_done:
+        ret = ssl_hs_ok;
+        break;
+    }
+
+    if (hs->tls13_state != state) {
+      ssl_do_info_callback(hs->ssl, SSL_CB_ACCEPT_LOOP, 1);
+    }
+
+    if (ret != ssl_hs_ok) {
+      return ret;
+    }
+  }
+
+  return ssl_hs_ok;
+}
+
+const char *tls13_server_handshake_state(SSL_HANDSHAKE *hs) {
+  enum tls13_server_hs_state_t state =
+      static_cast<enum tls13_server_hs_state_t>(hs->tls13_state);
+  switch (state) {
+    case state13_select_parameters:
+      return "TLS 1.3 server select_parameters";
+    case state13_select_session:
+      return "TLS 1.3 server select_session";
+    case state13_send_hello_retry_request:
+      return "TLS 1.3 server send_hello_retry_request";
+    case state13_read_second_client_hello:
+      return "TLS 1.3 server read_second_client_hello";
+    case state13_send_server_hello:
+      return "TLS 1.3 server send_server_hello";
+    case state13_send_server_certificate_verify:
+      return "TLS 1.3 server send_server_certificate_verify";
+    case state13_send_half_rtt_ticket:
+      return "TLS 1.3 server send_half_rtt_ticket";
+    case state13_send_server_finished:
+      return "TLS 1.3 server send_server_finished";
+    case state13_read_second_client_flight:
+      return "TLS 1.3 server read_second_client_flight";
+    case state13_process_end_of_early_data:
+      return "TLS 1.3 server process_end_of_early_data";
+    case state13_read_client_encrypted_extensions:
+      return "TLS 1.3 server read_client_encrypted_extensions";
+    case state13_read_client_certificate:
+      return "TLS 1.3 server read_client_certificate";
+    case state13_read_client_certificate_verify:
+      return "TLS 1.3 server read_client_certificate_verify";
+    case state13_read_channel_id:
+      return "TLS 1.3 server read_channel_id";
+    case state13_read_client_finished:
+      return "TLS 1.3 server read_client_finished";
+    case state13_send_new_session_ticket:
+      return "TLS 1.3 server send_new_session_ticket";
+    case state13_done:
+      return "TLS 1.3 server done";
+  }
+
+  return "TLS 1.3 server unknown";
+}
+
+BSSL_NAMESPACE_END