boringssl/ssl/tls13_client.cc

/* 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 <limits.h>
#include <string.h>

#include <utility>

#include <openssl/bytestring.h>
#include <openssl/digest.h>
#include <openssl/err.h>
#include <openssl/mem.h>
#include <openssl/stack.h>

#include "../crypto/internal.h"
#include "internal.h"


namespace bssl {

enum client_hs_state_t {
  state_read_hello_retry_request = 0,
  state_send_second_client_hello,
  state_read_server_hello,
  state_read_encrypted_extensions,
  state_read_certificate_request,
  state_read_server_certificate,
  state_read_server_certificate_verify,
  state_read_server_finished,
  state_send_end_of_early_data,
  state_send_client_certificate,
  state_send_client_certificate_verify,
  state_complete_second_flight,
  state_done,
};

static const uint8_t kZeroes[EVP_MAX_MD_SIZE] = {0};

static enum ssl_hs_wait_t do_read_hello_retry_request(SSL_HANDSHAKE *hs) {
  SSL *const ssl = hs->ssl;
  assert(ssl->s3->have_version);
  SSLMessage msg;
  if (!ssl->method->get_message(ssl, &msg)) {
    return ssl_hs_read_message;
  }

  // Queue up a ChangeCipherSpec for whenever we next send something. This
  // will be before the second ClientHello. If we offered early data, this was
  // already done.
  if (!hs->early_data_offered &&
      !ssl->method->add_change_cipher_spec(ssl)) {
    return ssl_hs_error;
  }

  if (!ssl_check_message_type(ssl, msg, SSL3_MT_SERVER_HELLO)) {
    return ssl_hs_error;
  }

  CBS body = msg.body, extensions, server_random, session_id;
  uint16_t server_version, cipher_suite;
  uint8_t compression_method;
  if (!CBS_get_u16(&body, &server_version) ||
      !CBS_get_bytes(&body, &server_random, SSL3_RANDOM_SIZE) ||
      !CBS_get_u8_length_prefixed(&body, &session_id) ||
      !CBS_mem_equal(&session_id, hs->session_id, hs->session_id_len) ||
      !CBS_get_u16(&body, &cipher_suite) ||
      !CBS_get_u8(&body, &compression_method) ||
      compression_method != 0 ||
      !CBS_get_u16_length_prefixed(&body, &extensions) ||
      CBS_len(&extensions) == 0 ||
      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;
  }

  if (!CBS_mem_equal(&server_random, kHelloRetryRequest, SSL3_RANDOM_SIZE)) {
    hs->tls13_state = state_read_server_hello;
    return ssl_hs_ok;
  }

  const SSL_CIPHER *cipher = SSL_get_cipher_by_value(cipher_suite);
  // Check if the cipher is a TLS 1.3 cipher.
  if (cipher == NULL ||
      SSL_CIPHER_get_min_version(cipher) > ssl_protocol_version(ssl) ||
      SSL_CIPHER_get_max_version(cipher) < ssl_protocol_version(ssl)) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_CIPHER_RETURNED);
    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
    return ssl_hs_error;
  }

  hs->new_cipher = cipher;

  if (!hs->transcript.InitHash(ssl_protocol_version(ssl), hs->new_cipher) ||
      !hs->transcript.UpdateForHelloRetryRequest()) {
    return ssl_hs_error;
  }


  bool have_cookie, have_key_share, have_supported_versions;
  CBS cookie, key_share, supported_versions;
  SSL_EXTENSION_TYPE ext_types[] = {
      {TLSEXT_TYPE_key_share, &have_key_share, &key_share},
      {TLSEXT_TYPE_cookie, &have_cookie, &cookie},
      {TLSEXT_TYPE_supported_versions, &have_supported_versions,
       &supported_versions},
  };

  uint8_t alert = SSL_AD_DECODE_ERROR;
  if (!ssl_parse_extensions(&extensions, &alert, ext_types,
                            OPENSSL_ARRAY_SIZE(ext_types),
                            0 /* reject unknown */)) {
    ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
    return ssl_hs_error;
  }

  if (!have_cookie && !have_key_share) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_EMPTY_HELLO_RETRY_REQUEST);
    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
    return ssl_hs_error;
  }
  if (have_cookie) {
    CBS cookie_value;
    if (!CBS_get_u16_length_prefixed(&cookie, &cookie_value) ||
        CBS_len(&cookie_value) == 0 ||
        CBS_len(&cookie) != 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 (!hs->cookie.CopyFrom(cookie_value)) {
      return ssl_hs_error;
    }
  }

  if (have_key_share) {
    uint16_t group_id;
    if (!CBS_get_u16(&key_share, &group_id) || CBS_len(&key_share) != 0) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
      return ssl_hs_error;
    }

    // The group must be supported.
    if (!tls1_check_group_id(hs, group_id)) {
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
      OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_CURVE);
      return ssl_hs_error;
    }

    // Check that the HelloRetryRequest does not request the key share that
    // was provided in the initial ClientHello.
    if (hs->key_share->GroupID() == group_id) {
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
      OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_CURVE);
      return ssl_hs_error;
    }

    hs->key_share.reset();
    hs->retry_group = group_id;
  }

  if (!ssl_hash_message(hs, msg)) {
    return ssl_hs_error;
  }

  ssl->method->next_message(ssl);
  hs->received_hello_retry_request = true;
  hs->tls13_state = state_send_second_client_hello;
  // 0-RTT is rejected if we receive a HelloRetryRequest.
  if (hs->in_early_data) {
    return ssl_hs_early_data_rejected;
  }
  return ssl_hs_ok;
}

static enum ssl_hs_wait_t do_send_second_client_hello(SSL_HANDSHAKE *hs) {
  SSL *const ssl = hs->ssl;
  // Restore the null cipher. We may have switched due to 0-RTT.
  bssl::UniquePtr<SSLAEADContext> null_ctx =
      SSLAEADContext::CreateNullCipher(SSL_is_dtls(ssl));
  if (!null_ctx ||
      !ssl->method->set_write_state(ssl, std::move(null_ctx))) {
    return ssl_hs_error;
  }

  ssl->s3->aead_write_ctx->SetVersionIfNullCipher(ssl->version);

  if (!ssl_write_client_hello(hs)) {
    return ssl_hs_error;
  }

  hs->tls13_state = state_read_server_hello;
  return ssl_hs_flush;
}

static enum ssl_hs_wait_t do_read_server_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_SERVER_HELLO)) {
    return ssl_hs_error;
  }

  CBS body = msg.body, server_random, session_id, extensions;
  uint16_t server_version;
  uint16_t cipher_suite;
  uint8_t compression_method;
  if (!CBS_get_u16(&body, &server_version) ||
      !CBS_get_bytes(&body, &server_random, SSL3_RANDOM_SIZE) ||
      !CBS_get_u8_length_prefixed(&body, &session_id) ||
      !CBS_mem_equal(&session_id, hs->session_id, hs->session_id_len) ||
      !CBS_get_u16(&body, &cipher_suite) ||
      !CBS_get_u8(&body, &compression_method) ||
      compression_method != 0 ||
      !CBS_get_u16_length_prefixed(&body, &extensions) ||
      CBS_len(&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;
  }

  if (server_version != TLS1_2_VERSION) {
    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
    OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_VERSION_NUMBER);
    return ssl_hs_error;
  }

  // Forbid a second HelloRetryRequest.
  if (CBS_mem_equal(&server_random, kHelloRetryRequest, SSL3_RANDOM_SIZE)) {
    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_UNEXPECTED_MESSAGE);
    OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_MESSAGE);
    return ssl_hs_error;
  }

  OPENSSL_memcpy(ssl->s3->server_random, CBS_data(&server_random),
                 SSL3_RANDOM_SIZE);

  // Check if the cipher is a TLS 1.3 cipher.
  const SSL_CIPHER *cipher = SSL_get_cipher_by_value(cipher_suite);
  if (cipher == nullptr ||
      SSL_CIPHER_get_min_version(cipher) > ssl_protocol_version(ssl) ||
      SSL_CIPHER_get_max_version(cipher) < ssl_protocol_version(ssl)) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_CIPHER_RETURNED);
    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
    return ssl_hs_error;
  }

  // Check that the cipher matches the one in the HelloRetryRequest.
  if (hs->received_hello_retry_request &&
      hs->new_cipher != cipher) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_CIPHER_RETURNED);
    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
    return ssl_hs_error;
  }

  // Parse out the extensions.
  bool have_key_share = false, have_pre_shared_key = false,
       have_supported_versions = false;
  CBS key_share, pre_shared_key, supported_versions;
  SSL_EXTENSION_TYPE ext_types[] = {
      {TLSEXT_TYPE_key_share, &have_key_share, &key_share},
      {TLSEXT_TYPE_pre_shared_key, &have_pre_shared_key, &pre_shared_key},
      {TLSEXT_TYPE_supported_versions, &have_supported_versions,
       &supported_versions},
  };

  uint8_t alert = SSL_AD_DECODE_ERROR;
  if (!ssl_parse_extensions(&extensions, &alert, ext_types,
                            OPENSSL_ARRAY_SIZE(ext_types),
                            0 /* reject unknown */)) {
    ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
    return ssl_hs_error;
  }

  if (ssl_is_draft28(ssl->version)) {
    // Recheck supported_versions, in case this is the second ServerHello.
    uint16_t version;
    if (!have_supported_versions ||
        !CBS_get_u16(&supported_versions, &version) ||
        version != ssl->version) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_SECOND_SERVERHELLO_VERSION_MISMATCH);
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
      return ssl_hs_error;
    }
  }

  alert = SSL_AD_DECODE_ERROR;
  if (have_pre_shared_key) {
    if (ssl->session == NULL) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_EXTENSION);
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_UNSUPPORTED_EXTENSION);
      return ssl_hs_error;
    }

    if (!ssl_ext_pre_shared_key_parse_serverhello(hs, &alert,
                                                  &pre_shared_key)) {
      ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
      return ssl_hs_error;
    }

    if (ssl->session->ssl_version != ssl->version) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_OLD_SESSION_VERSION_NOT_RETURNED);
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
      return ssl_hs_error;
    }

    if (ssl->session->cipher->algorithm_prf != cipher->algorithm_prf) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_OLD_SESSION_PRF_HASH_MISMATCH);
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
      return ssl_hs_error;
    }

    if (!ssl_session_is_context_valid(hs, ssl->session)) {
      // This is actually a client application bug.
      OPENSSL_PUT_ERROR(SSL,
                        SSL_R_ATTEMPT_TO_REUSE_SESSION_IN_DIFFERENT_CONTEXT);
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
      return ssl_hs_error;
    }

    ssl->s3->session_reused = true;
    // Only authentication information carries over in TLS 1.3.
    hs->new_session = SSL_SESSION_dup(ssl->session, SSL_SESSION_DUP_AUTH_ONLY);
    if (!hs->new_session) {
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
      return ssl_hs_error;
    }
    ssl_set_session(ssl, NULL);

    // 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);
  } else if (!ssl_get_new_session(hs, 0)) {
    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
    return ssl_hs_error;
  }

  hs->new_session->cipher = cipher;
  hs->new_cipher = cipher;

  size_t hash_len =
      EVP_MD_size(ssl_get_handshake_digest(ssl_protocol_version(ssl), cipher));

  // Set up the key schedule and incorporate the PSK into the running secret.
  if (ssl->s3->session_reused) {
    if (!tls13_init_key_schedule(hs, hs->new_session->master_key,
                                 hs->new_session->master_key_length)) {
      return ssl_hs_error;
    }
  } else if (!tls13_init_key_schedule(hs, kZeroes, hash_len)) {
    return ssl_hs_error;
  }

  if (!have_key_share) {
    // We do not support psk_ke and thus always require a key share.
    OPENSSL_PUT_ERROR(SSL, SSL_R_MISSING_KEY_SHARE);
    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_MISSING_EXTENSION);
    return ssl_hs_error;
  }

  // Resolve ECDHE and incorporate it into the secret.
  Array<uint8_t> dhe_secret;
  alert = SSL_AD_DECODE_ERROR;
  if (!ssl_ext_key_share_parse_serverhello(hs, &dhe_secret, &alert,
                                           &key_share)) {
    ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
    return ssl_hs_error;
  }

  if (!tls13_advance_key_schedule(hs, dhe_secret.data(), dhe_secret.size()) ||
      !ssl_hash_message(hs, msg) ||
      !tls13_derive_handshake_secrets(hs) ||
      !tls13_set_traffic_key(ssl, evp_aead_open, hs->server_handshake_secret,
                             hs->hash_len)) {
    return ssl_hs_error;
  }

  if (!hs->early_data_offered) {
    // If not sending early data, set client traffic keys now so that alerts are
    // encrypted.
    if (!tls13_set_traffic_key(ssl, evp_aead_seal, hs->client_handshake_secret,
                               hs->hash_len)) {
      return ssl_hs_error;
    }
  }

  ssl->method->next_message(ssl);
  hs->tls13_state = state_read_encrypted_extensions;
  return ssl_hs_ok;
}

static enum ssl_hs_wait_t do_read_encrypted_extensions(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_ENCRYPTED_EXTENSIONS)) {
    return ssl_hs_error;
  }

  CBS body = msg.body;
  if (!ssl_parse_serverhello_tlsext(hs, &body)) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_PARSE_TLSEXT);
    return ssl_hs_error;
  }
  if (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;
  }

  // Store the negotiated ALPN in the session.
  if (!ssl->s3->alpn_selected.empty()) {
    hs->new_session->early_alpn = (uint8_t *)BUF_memdup(
        ssl->s3->alpn_selected.data(), ssl->s3->alpn_selected.size());
    if (hs->new_session->early_alpn == NULL) {
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
      return ssl_hs_error;
    }
    hs->new_session->early_alpn_len = ssl->s3->alpn_selected.size();
  }

  if (ssl->s3->early_data_accepted) {
    if (hs->early_session->cipher != hs->new_session->cipher ||
        MakeConstSpan(hs->early_session->early_alpn,
                      hs->early_session->early_alpn_len) !=
            ssl->s3->alpn_selected) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_ALPN_MISMATCH_ON_EARLY_DATA);
      return ssl_hs_error;
    }
    if (ssl->s3->tlsext_channel_id_valid || hs->received_custom_extension ||
        ssl->s3->token_binding_negotiated) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_EXTENSION_ON_EARLY_DATA);
      return ssl_hs_error;
    }
  }

  if (!ssl_hash_message(hs, msg)) {
    return ssl_hs_error;
  }

  ssl->method->next_message(ssl);
  hs->tls13_state = state_read_certificate_request;
  if (hs->in_early_data && !ssl->s3->early_data_accepted) {
    return ssl_hs_early_data_rejected;
  }
  return ssl_hs_ok;
}

static enum ssl_hs_wait_t do_read_certificate_request(SSL_HANDSHAKE *hs) {
  SSL *const ssl = hs->ssl;
  // CertificateRequest may only be sent in non-resumption handshakes.
  if (ssl->s3->session_reused) {
    hs->tls13_state = state_read_server_finished;
    return ssl_hs_ok;
  }

  SSLMessage msg;
  if (!ssl->method->get_message(ssl, &msg)) {
    return ssl_hs_read_message;
  }

  // CertificateRequest is optional.
  if (msg.type != SSL3_MT_CERTIFICATE_REQUEST) {
    hs->tls13_state = state_read_server_certificate;
    return ssl_hs_ok;
  }


  bool have_sigalgs = false, have_ca = false;
  CBS sigalgs, ca;
  const SSL_EXTENSION_TYPE ext_types[] = {
    {TLSEXT_TYPE_signature_algorithms, &have_sigalgs, &sigalgs},
    {TLSEXT_TYPE_certificate_authorities, &have_ca, &ca},
  };

  CBS body = msg.body, context, extensions, supported_signature_algorithms;
  uint8_t alert = SSL_AD_DECODE_ERROR;
  if (!CBS_get_u8_length_prefixed(&body, &context) ||
      // The request context is always empty during the handshake.
      CBS_len(&context) != 0 ||
      !CBS_get_u16_length_prefixed(&body, &extensions) ||
      CBS_len(&body) != 0 ||
      !ssl_parse_extensions(&extensions, &alert, ext_types,
                            OPENSSL_ARRAY_SIZE(ext_types),
                            1 /* accept unknown */) ||
      (have_ca && CBS_len(&ca) == 0) ||
      !have_sigalgs ||
      !CBS_get_u16_length_prefixed(&sigalgs,
                                   &supported_signature_algorithms) ||
      CBS_len(&supported_signature_algorithms) == 0 ||
      !tls1_parse_peer_sigalgs(hs, &supported_signature_algorithms)) {
    ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
    OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
    return ssl_hs_error;
  }

  if (have_ca) {
    hs->ca_names = ssl_parse_client_CA_list(ssl, &alert, &ca);
    if (!hs->ca_names) {
      ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
      return ssl_hs_error;
    }
  } else {
    hs->ca_names.reset(sk_CRYPTO_BUFFER_new_null());
    if (!hs->ca_names) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
      return ssl_hs_error;
    }
  }

  hs->cert_request = true;
  ssl->ctx->x509_method->hs_flush_cached_ca_names(hs);

  if (!ssl_hash_message(hs, msg)) {
    return ssl_hs_error;
  }

  ssl->method->next_message(ssl);
  hs->tls13_state = state_read_server_certificate;
  return ssl_hs_ok;
}

static enum ssl_hs_wait_t do_read_server_certificate(SSL_HANDSHAKE *hs) {
  SSL *const ssl = hs->ssl;
  SSLMessage msg;
  if (!ssl->method->get_message(ssl, &msg)) {
    return ssl_hs_read_message;
  }

  if (msg.type != SSL3_MT_COMPRESSED_CERTIFICATE &&
      !ssl_check_message_type(ssl, msg, SSL3_MT_CERTIFICATE)) {
    return ssl_hs_error;
  }

  if (!tls13_process_certificate(hs, msg, 0 /* certificate required */) ||
      !ssl_hash_message(hs, msg)) {
    return ssl_hs_error;
  }

  ssl->method->next_message(ssl);
  hs->tls13_state = state_read_server_certificate_verify;
  return ssl_hs_ok;
}

static enum ssl_hs_wait_t do_read_server_certificate_verify(
    SSL_HANDSHAKE *hs) {
  SSL *const ssl = hs->ssl;
  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 = state_read_server_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 = state_read_server_finished;
  return ssl_hs_ok;
}

static enum ssl_hs_wait_t do_read_server_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) ||
      !tls13_process_finished(hs, msg, 0 /* don't use saved value */) ||
      !ssl_hash_message(hs, msg) ||
      // Update the secret to the master secret and derive traffic keys.
      !tls13_advance_key_schedule(hs, kZeroes, hs->hash_len) ||
      !tls13_derive_application_secrets(hs)) {
    return ssl_hs_error;
  }

  ssl->method->next_message(ssl);
  hs->tls13_state = state_send_end_of_early_data;
  return ssl_hs_ok;
}

static enum ssl_hs_wait_t do_send_end_of_early_data(SSL_HANDSHAKE *hs) {
  SSL *const ssl = hs->ssl;

  if (ssl->s3->early_data_accepted) {
    hs->can_early_write = false;
    ScopedCBB cbb;
    CBB body;
    if (!ssl->method->init_message(ssl, cbb.get(), &body,
                                   SSL3_MT_END_OF_EARLY_DATA) ||
        !ssl_add_message_cbb(ssl, cbb.get())) {
      return ssl_hs_error;
    }
  }

  if (hs->early_data_offered) {
    if (!tls13_set_traffic_key(ssl, evp_aead_seal, hs->client_handshake_secret,
                               hs->hash_len)) {
      return ssl_hs_error;
    }
  }

  hs->tls13_state = state_send_client_certificate;
  return ssl_hs_ok;
}

static enum ssl_hs_wait_t do_send_client_certificate(SSL_HANDSHAKE *hs) {
  SSL *const ssl = hs->ssl;

  // The peer didn't request a certificate.
  if (!hs->cert_request) {
    hs->tls13_state = state_complete_second_flight;
    return ssl_hs_ok;
  }

  // Call cert_cb to update the certificate.
  if (hs->config->cert->cert_cb != NULL) {
    int rv = hs->config->cert->cert_cb(ssl, hs->config->cert->cert_cb_arg);
    if (rv == 0) {
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
      OPENSSL_PUT_ERROR(SSL, SSL_R_CERT_CB_ERROR);
      return ssl_hs_error;
    }
    if (rv < 0) {
      hs->tls13_state = state_send_client_certificate;
      return ssl_hs_x509_lookup;
    }
  }

  if (!ssl_on_certificate_selected(hs) ||
      !tls13_add_certificate(hs)) {
    return ssl_hs_error;
  }

  hs->tls13_state = state_send_client_certificate_verify;
  return ssl_hs_ok;
}

static enum ssl_hs_wait_t do_send_client_certificate_verify(SSL_HANDSHAKE *hs) {
  // Don't send CertificateVerify if there is no certificate.
  if (!ssl_has_certificate(hs->config)) {
    hs->tls13_state = state_complete_second_flight;
    return ssl_hs_ok;
  }

  switch (tls13_add_certificate_verify(hs)) {
    case ssl_private_key_success:
      hs->tls13_state = state_complete_second_flight;
      return ssl_hs_ok;

    case ssl_private_key_retry:
      hs->tls13_state = state_send_client_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_complete_second_flight(SSL_HANDSHAKE *hs) {
  SSL *const ssl = hs->ssl;

  // Send a Channel ID assertion if necessary.
  if (ssl->s3->tlsext_channel_id_valid) {
    if (!ssl_do_channel_id_callback(hs)) {
      hs->tls13_state = state_complete_second_flight;
      return ssl_hs_error;
    }

    if (hs->config->tlsext_channel_id_private == NULL) {
      return ssl_hs_channel_id_lookup;
    }

    ScopedCBB cbb;
    CBB body;
    if (!ssl->method->init_message(ssl, cbb.get(), &body, SSL3_MT_CHANNEL_ID) ||
        !tls1_write_channel_id(hs, &body) ||
        !ssl_add_message_cbb(ssl, cbb.get())) {
      return ssl_hs_error;
    }
  }

  // Send a Finished message.
  if (!tls13_add_finished(hs)) {
    return ssl_hs_error;
  }

  // Derive the final keys and enable them.
  if (!tls13_set_traffic_key(ssl, evp_aead_open, hs->server_traffic_secret_0,
                             hs->hash_len) ||
      !tls13_set_traffic_key(ssl, evp_aead_seal, hs->client_traffic_secret_0,
                             hs->hash_len) ||
      !tls13_derive_resumption_secret(hs)) {
    return ssl_hs_error;
  }

  hs->tls13_state = state_done;
  return ssl_hs_flush;
}

enum ssl_hs_wait_t tls13_client_handshake(SSL_HANDSHAKE *hs) {
  while (hs->tls13_state != state_done) {
    enum ssl_hs_wait_t ret = ssl_hs_error;
    enum client_hs_state_t state =
        static_cast<enum client_hs_state_t>(hs->tls13_state);
    switch (state) {
      case state_read_hello_retry_request:
        ret = do_read_hello_retry_request(hs);
        break;
      case state_send_second_client_hello:
        ret = do_send_second_client_hello(hs);
        break;
      case state_read_server_hello:
        ret = do_read_server_hello(hs);
        break;
      case state_read_encrypted_extensions:
        ret = do_read_encrypted_extensions(hs);
        break;
      case state_read_certificate_request:
        ret = do_read_certificate_request(hs);
        break;
      case state_read_server_certificate:
        ret = do_read_server_certificate(hs);
        break;
      case state_read_server_certificate_verify:
        ret = do_read_server_certificate_verify(hs);
        break;
      case state_read_server_finished:
        ret = do_read_server_finished(hs);
        break;
      case state_send_end_of_early_data:
        ret = do_send_end_of_early_data(hs);
        break;
      case state_send_client_certificate:
        ret = do_send_client_certificate(hs);
        break;
      case state_send_client_certificate_verify:
        ret = do_send_client_certificate_verify(hs);
        break;
      case state_complete_second_flight:
        ret = do_complete_second_flight(hs);
        break;
      case state_done:
        ret = ssl_hs_ok;
        break;
    }

    if (hs->tls13_state != state) {
      ssl_do_info_callback(hs->ssl, SSL_CB_CONNECT_LOOP, 1);
    }

    if (ret != ssl_hs_ok) {
      return ret;
    }
  }

  return ssl_hs_ok;
}

const char *tls13_client_handshake_state(SSL_HANDSHAKE *hs) {
  enum client_hs_state_t state =
      static_cast<enum client_hs_state_t>(hs->tls13_state);
  switch (state) {
    case state_read_hello_retry_request:
      return "TLS 1.3 client read_hello_retry_request";
    case state_send_second_client_hello:
      return "TLS 1.3 client send_second_client_hello";
    case state_read_server_hello:
      return "TLS 1.3 client read_server_hello";
    case state_read_encrypted_extensions:
      return "TLS 1.3 client read_encrypted_extensions";
    case state_read_certificate_request:
      return "TLS 1.3 client read_certificate_request";
    case state_read_server_certificate:
      return "TLS 1.3 client read_server_certificate";
    case state_read_server_certificate_verify:
      return "TLS 1.3 client read_server_certificate_verify";
    case state_read_server_finished:
      return "TLS 1.3 client read_server_finished";
    case state_send_end_of_early_data:
      return "TLS 1.3 client send_end_of_early_data";
    case state_send_client_certificate:
      return "TLS 1.3 client send_client_certificate";
    case state_send_client_certificate_verify:
      return "TLS 1.3 client send_client_certificate_verify";
    case state_complete_second_flight:
      return "TLS 1.3 client complete_second_flight";
    case state_done:
      return "TLS 1.3 client done";
  }

  return "TLS 1.3 client unknown";
}

int tls13_process_new_session_ticket(SSL *ssl, const SSLMessage &msg) {
  if (ssl->s3->write_shutdown != ssl_shutdown_none) {
    // Ignore tickets on shutdown. Callers tend to indiscriminately call
    // |SSL_shutdown| before destroying an |SSL|, at which point calling the new
    // session callback may be confusing.
    return 1;
  }

  UniquePtr<SSL_SESSION> session = SSL_SESSION_dup(
      ssl->s3->established_session.get(), SSL_SESSION_INCLUDE_NONAUTH);
  if (!session) {
    return 0;
  }

  ssl_session_rebase_time(ssl, session.get());

  uint32_t server_timeout;
  CBS body = msg.body, ticket_nonce, ticket, extensions;
  if (!CBS_get_u32(&body, &server_timeout) ||
      !CBS_get_u32(&body, &session->ticket_age_add) ||
      !CBS_get_u8_length_prefixed(&body, &ticket_nonce) ||
      !CBS_get_u16_length_prefixed(&body, &ticket) ||
      !CBS_stow(&ticket, &session->tlsext_tick, &session->tlsext_ticklen) ||
      !CBS_get_u16_length_prefixed(&body, &extensions) ||
      CBS_len(&body) != 0) {
    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
    OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
    return 0;
  }

  // Cap the renewable lifetime by the server advertised value. This avoids
  // wasting bandwidth on 0-RTT when we know the server will reject it.
  if (session->timeout > server_timeout) {
    session->timeout = server_timeout;
  }

  if (!tls13_derive_session_psk(session.get(), ticket_nonce)) {
    return 0;
  }

  // Parse out the extensions.
  bool have_early_data_info = false;
  CBS early_data_info;
  const SSL_EXTENSION_TYPE ext_types[] = {
      {TLSEXT_TYPE_early_data, &have_early_data_info, &early_data_info},
  };

  uint8_t alert = SSL_AD_DECODE_ERROR;
  if (!ssl_parse_extensions(&extensions, &alert, ext_types,
                            OPENSSL_ARRAY_SIZE(ext_types),
                            1 /* ignore unknown */)) {
    ssl_send_alert(ssl, SSL3_AL_FATAL, alert);
    return 0;
  }

  if (have_early_data_info && ssl->enable_early_data) {
    if (!CBS_get_u32(&early_data_info, &session->ticket_max_early_data) ||
        CBS_len(&early_data_info) != 0) {
      ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
      OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
      return 0;
    }
  }

  session->ticket_age_add_valid = 1;
  session->not_resumable = 0;

  if ((ssl->session_ctx->session_cache_mode & SSL_SESS_CACHE_CLIENT) &&
      ssl->session_ctx->new_session_cb != NULL &&
      ssl->session_ctx->new_session_cb(ssl, session.get())) {
    // |new_session_cb|'s return value signals that it took ownership.
    session.release();
  }

  return 1;
}

}  // namespace bssl