text: /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   * All rights reserved.
   *
   * This package is an SSL implementation written
   * by Eric Young (eay@cryptsoft.com).
   * The implementation was written so as to conform with Netscapes SSL.
   * 
   * This library is free for commercial and non-commercial use as long as
   * the following conditions are aheared to.  The following conditions
   * apply to all code found in this distribution, be it the RC4, RSA,
   * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
   * included with this distribution is covered by the same copyright terms
   * except that the holder is Tim Hudson (tjh@cryptsoft.com).
   * 
   * Copyright remains Eric Young's, and as such any Copyright notices in
   * the code are not to be removed.
   * If this package is used in a product, Eric Young should be given attribution
   * as the author of the parts of the library used.
   * This can be in the form of a textual message at program startup or
   * in documentation (online or textual) provided with the package.
   * 
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. All advertising materials mentioning features or use of this software
   *    must display the following acknowledgement:
   *    "This product includes cryptographic software written by
   *     Eric Young (eay@cryptsoft.com)"
   *    The word 'cryptographic' can be left out if the rouines from the library
   *    being used are not cryptographic related :-).
   * 4. If you include any Windows specific code (or a derivative thereof) from 
   *    the apps directory (application code) you must include an acknowledgement:
   *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
   * 
   * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   * 
   * The licence and distribution terms for any publically available version or
   * derivative of this code cannot be changed.  i.e. this code cannot simply be
   * copied and put under another distribution licence
   * [including the GNU Public Licence.]
   */
  /* ====================================================================
   * Copyright (c) 1998-2007 The OpenSSL Project.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer. 
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. All advertising materials mentioning features or use of this
   *    software must display the following acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
   *
   * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
   *    endorse or promote products derived from this software without
   *    prior written permission. For written permission, please contact
   *    openssl-core@openssl.org.
   *
   * 5. Products derived from this software may not be called "OpenSSL"
   *    nor may "OpenSSL" appear in their names without prior written
   *    permission of the OpenSSL Project.
   *
   * 6. Redistributions of any form whatsoever must retain the following
   *    acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
   *
   * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
   * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
   * OF THE POSSIBILITY OF SUCH DAMAGE.
   * ====================================================================
   *
   * This product includes cryptographic software written by Eric Young
   * (eay@cryptsoft.com).  This product includes software written by Tim
   * Hudson (tjh@cryptsoft.com). */
  
  #include <openssl/ssl.h>
  
  #include <assert.h>
  #include <limits.h>
  #include <stdlib.h>
  #include <string.h>
  
  #include <openssl/bytestring.h>
  #include <openssl/digest.h>
  #include <openssl/err.h>
  #include <openssl/evp.h>
  #include <openssl/hmac.h>
  #include <openssl/mem.h>
  #include <openssl/nid.h>
  #include <openssl/rand.h>
  #include <openssl/type_check.h>
  
  #include "internal.h"
  #include "../crypto/internal.h"
  
  
  static int ssl_check_clienthello_tlsext(SSL *ssl);
  static int ssl_check_serverhello_tlsext(SSL *ssl);
  
  static int compare_uint16_t(const void *p1, const void *p2) {
    uint16_t u1 = *((const uint16_t *)p1);
    uint16_t u2 = *((const uint16_t *)p2);
    if (u1 < u2) {
      return -1;
    } else if (u1 > u2) {
      return 1;
    } else {
      return 0;
    }
  }
  
  /* Per http://tools.ietf.org/html/rfc5246#section-7.4.1.4, there may not be
   * more than one extension of the same type in a ClientHello or ServerHello.
   * This function does an initial scan over the extensions block to filter those
   * out. */
  static int tls1_check_duplicate_extensions(const CBS *cbs) {
    CBS extensions = *cbs;
    size_t num_extensions = 0, i = 0;
    uint16_t *extension_types = NULL;
    int ret = 0;
  
    /* First pass: count the extensions. */
    while (CBS_len(&extensions) > 0) {
      uint16_t type;
      CBS extension;
  
      if (!CBS_get_u16(&extensions, &type) ||
          !CBS_get_u16_length_prefixed(&extensions, &extension)) {
        goto done;
      }
  
      num_extensions++;
    }
  
    if (num_extensions == 0) {
      return 1;
    }
  
    extension_types = OPENSSL_malloc(sizeof(uint16_t) * num_extensions);
    if (extension_types == NULL) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
      goto done;
    }
  
    /* Second pass: gather the extension types. */
    extensions = *cbs;
    for (i = 0; i < num_extensions; i++) {
      CBS extension;
  
      if (!CBS_get_u16(&extensions, &extension_types[i]) ||
          !CBS_get_u16_length_prefixed(&extensions, &extension)) {
        /* This should not happen. */
        goto done;
      }
    }
    assert(CBS_len(&extensions) == 0);
  
    /* Sort the extensions and make sure there are no duplicates. */
    qsort(extension_types, num_extensions, sizeof(uint16_t), compare_uint16_t);
    for (i = 1; i < num_extensions; i++) {
      if (extension_types[i - 1] == extension_types[i]) {
        goto done;
      }
    }
  
    ret = 1;
  
  done:
    OPENSSL_free(extension_types);
    return ret;
  }
  
  int ssl_early_callback_init(SSL *ssl, struct ssl_early_callback_ctx *ctx,
                              const uint8_t *in, size_t in_len) {
    memset(ctx, 0, sizeof(*ctx));
    ctx->ssl = ssl;
    ctx->client_hello = in;
    ctx->client_hello_len = in_len;
  
    CBS client_hello, random, session_id;
    CBS_init(&client_hello, ctx->client_hello, ctx->client_hello_len);
    if (!CBS_get_u16(&client_hello, &ctx->version) ||
        !CBS_get_bytes(&client_hello, &random, SSL3_RANDOM_SIZE) ||
        !CBS_get_u8_length_prefixed(&client_hello, &session_id) ||
        CBS_len(&session_id) > SSL_MAX_SSL_SESSION_ID_LENGTH) {
      return 0;
    }
  
    ctx->random = CBS_data(&random);
    ctx->random_len = CBS_len(&random);
    ctx->session_id = CBS_data(&session_id);
    ctx->session_id_len = CBS_len(&session_id);
  
    /* Skip past DTLS cookie */
    if (SSL_is_dtls(ctx->ssl)) {
      CBS cookie;
      if (!CBS_get_u8_length_prefixed(&client_hello, &cookie) ||
          CBS_len(&cookie) > DTLS1_COOKIE_LENGTH) {
        return 0;
      }
    }
  
    CBS cipher_suites, compression_methods;
    if (!CBS_get_u16_length_prefixed(&client_hello, &cipher_suites) ||
        CBS_len(&cipher_suites) < 2 || (CBS_len(&cipher_suites) & 1) != 0 ||
        !CBS_get_u8_length_prefixed(&client_hello, &compression_methods) ||
        CBS_len(&compression_methods) < 1) {
      return 0;
    }
  
    ctx->cipher_suites = CBS_data(&cipher_suites);
    ctx->cipher_suites_len = CBS_len(&cipher_suites);
    ctx->compression_methods = CBS_data(&compression_methods);
    ctx->compression_methods_len = CBS_len(&compression_methods);
  
    /* If the ClientHello ends here then it's valid, but doesn't have any
     * extensions. (E.g. SSLv3.) */
    if (CBS_len(&client_hello) == 0) {
      ctx->extensions = NULL;
      ctx->extensions_len = 0;
      return 1;
    }
  
    /* Extract extensions and check it is valid. */
    CBS extensions;
    if (!CBS_get_u16_length_prefixed(&client_hello, &extensions) ||
        !tls1_check_duplicate_extensions(&extensions) ||
        CBS_len(&client_hello) != 0) {
      return 0;
    }
  
    ctx->extensions = CBS_data(&extensions);
    ctx->extensions_len = CBS_len(&extensions);
  
    return 1;
  }
  
  int ssl_early_callback_get_extension(const struct ssl_early_callback_ctx *ctx,
                                       CBS *out, uint16_t extension_type) {
    CBS extensions;
    CBS_init(&extensions, ctx->extensions, ctx->extensions_len);
    while (CBS_len(&extensions) != 0) {
      /* Decode the next extension. */
      uint16_t type;
      CBS extension;
      if (!CBS_get_u16(&extensions, &type) ||
          !CBS_get_u16_length_prefixed(&extensions, &extension)) {
        return 0;
      }
  
      if (type == extension_type) {
        *out = extension;
        return 1;
      }
    }
  
    return 0;
  }
  
  int SSL_early_callback_ctx_extension_get(
      const struct ssl_early_callback_ctx *ctx, uint16_t extension_type,
      const uint8_t **out_data, size_t *out_len) {
    CBS cbs;
    if (!ssl_early_callback_get_extension(ctx, &cbs, extension_type)) {
      return 0;
    }
  
    *out_data = CBS_data(&cbs);
    *out_len = CBS_len(&cbs);
    return 1;
  }
  
  static const uint16_t kDefaultGroups[] = {
      SSL_CURVE_X25519,
      SSL_CURVE_SECP256R1,
      SSL_CURVE_SECP384R1,
  #if defined(BORINGSSL_ANDROID_SYSTEM)
      SSL_CURVE_SECP521R1,
  #endif
  };
  
  void tls1_get_grouplist(SSL *ssl, int get_peer_groups,
                          const uint16_t **out_group_ids,
                          size_t *out_group_ids_len) {
    if (get_peer_groups) {
      /* Only clients send a supported group list, so this function is only
       * called on the server. */
      assert(ssl->server);
      *out_group_ids = ssl->s3->tmp.peer_supported_group_list;
      *out_group_ids_len = ssl->s3->tmp.peer_supported_group_list_len;
      return;
    }
  
    *out_group_ids = ssl->supported_group_list;
    *out_group_ids_len = ssl->supported_group_list_len;
    if (!*out_group_ids) {
      *out_group_ids = kDefaultGroups;
      *out_group_ids_len = OPENSSL_ARRAY_SIZE(kDefaultGroups);
    }
  }
  
  int tls1_get_shared_group(SSL *ssl, uint16_t *out_group_id) {
    const uint16_t *groups, *peer_groups, *pref, *supp;
    size_t groups_len, peer_groups_len, pref_len, supp_len, i, j;
  
    /* Can't do anything on client side */
    if (ssl->server == 0) {
      return 0;
    }
  
    tls1_get_grouplist(ssl, 0 /* local groups */, &groups, &groups_len);
    tls1_get_grouplist(ssl, 1 /* peer groups */, &peer_groups, &peer_groups_len);
  
    if (peer_groups_len == 0) {
      /* Clients are not required to send a supported_groups extension. In this
       * case, the server is free to pick any group it likes. See RFC 4492,
       * section 4, paragraph 3.
       *
       * However, in the interests of compatibility, we will skip ECDH if the
       * client didn't send an extension because we can't be sure that they'll
       * support our favoured group. */
      return 0;
    }
  
    if (ssl->options & SSL_OP_CIPHER_SERVER_PREFERENCE) {
      pref = groups;
      pref_len = groups_len;
      supp = peer_groups;
      supp_len = peer_groups_len;
    } else {
      pref = peer_groups;
      pref_len = peer_groups_len;
      supp = groups;
      supp_len = groups_len;
    }
  
    for (i = 0; i < pref_len; i++) {
      for (j = 0; j < supp_len; j++) {
        if (pref[i] == supp[j]) {
          *out_group_id = pref[i];
          return 1;
        }
      }
    }
  
    return 0;
  }
  
  int tls1_set_curves(uint16_t **out_group_ids, size_t *out_group_ids_len,
                      const int *curves, size_t ncurves) {
    uint16_t *group_ids;
  
    group_ids = OPENSSL_malloc(ncurves * sizeof(uint16_t));
    if (group_ids == NULL) {
      return 0;
    }
  
    for (size_t i = 0; i < ncurves; i++) {
      if (!ssl_nid_to_group_id(&group_ids[i], curves[i])) {
        OPENSSL_free(group_ids);
        return 0;
      }
    }
  
    OPENSSL_free(*out_group_ids);
    *out_group_ids = group_ids;
    *out_group_ids_len = ncurves;
  
    return 1;
  }
  
  /* tls1_curve_params_from_ec_key sets |*out_group_id| and |*out_comp_id| to the
   * TLS group ID and point format, respectively, for |ec|. It returns one on
   * success and zero on failure. */
  static int tls1_curve_params_from_ec_key(uint16_t *out_group_id,
                                           uint8_t *out_comp_id, EC_KEY *ec) {
    int nid;
    uint16_t id;
    const EC_GROUP *grp;
  
    if (ec == NULL) {
      return 0;
    }
  
    grp = EC_KEY_get0_group(ec);
    if (grp == NULL) {
      return 0;
    }
  
    /* Determine group ID */
    nid = EC_GROUP_get_curve_name(grp);
    if (!ssl_nid_to_group_id(&id, nid)) {
      return 0;
    }
  
    /* Set the named group ID. Arbitrary explicit groups are not supported. */
    *out_group_id = id;
  
    if (out_comp_id) {
      if (EC_KEY_get0_public_key(ec) == NULL) {
        return 0;
      }
      if (EC_KEY_get_conv_form(ec) == POINT_CONVERSION_COMPRESSED) {
        *out_comp_id = TLSEXT_ECPOINTFORMAT_ansiX962_compressed_prime;
      } else {
        *out_comp_id = TLSEXT_ECPOINTFORMAT_uncompressed;
      }
    }
  
    return 1;
  }
  
  /* tls1_check_group_id returns one if |group_id| is consistent with both our
   * and the peer's group preferences. Note: if called as the client, only our
   * preferences are checked; the peer (the server) does not send preferences. */
  int tls1_check_group_id(SSL *ssl, uint16_t group_id) {
    const uint16_t *groups;
    size_t groups_len, i, get_peer_groups;
  
    /* Check against our list, then the peer's list. */
    for (get_peer_groups = 0; get_peer_groups <= 1; get_peer_groups++) {
      if (get_peer_groups && !ssl->server) {
        /* Servers do not present a preference list so, if we are a client, only
         * check our list. */
        continue;
      }
  
      tls1_get_grouplist(ssl, get_peer_groups, &groups, &groups_len);
      if (get_peer_groups && groups_len == 0) {
        /* Clients are not required to send a supported_groups extension. In this
         * case, the server is free to pick any group it likes. See RFC 4492,
         * section 4, paragraph 3. */
        continue;
      }
      for (i = 0; i < groups_len; i++) {
        if (groups[i] == group_id) {
          break;
        }
      }
  
      if (i == groups_len) {
        return 0;
      }
    }
  
    return 1;
  }
  
  int tls1_check_ec_cert(SSL *ssl, X509 *x) {
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      /* In TLS 1.3, the ECDSA curve is negotiated via signature algorithms. */
      return 1;
    }
  
    EVP_PKEY *pkey = X509_get_pubkey(x);
    if (pkey == NULL) {
      return 0;
    }
  
    int ret = 0;
    uint16_t group_id;
    uint8_t comp_id;
    EC_KEY *ec_key = EVP_PKEY_get0_EC_KEY(pkey);
    if (ec_key == NULL ||
        !tls1_curve_params_from_ec_key(&group_id, &comp_id, ec_key) ||
        !tls1_check_group_id(ssl, group_id) ||
        comp_id != TLSEXT_ECPOINTFORMAT_uncompressed) {
      goto done;
    }
  
    ret = 1;
  
  done:
    EVP_PKEY_free(pkey);
    return ret;
  }
  
  /* List of supported signature algorithms and hashes. Should make this
   * customisable at some point, for now include everything we support. */
  
  static const uint16_t kDefaultSignatureAlgorithms[] = {
      SSL_SIGN_RSA_PKCS1_SHA512,
      SSL_SIGN_ECDSA_SECP521R1_SHA512,
  
      SSL_SIGN_RSA_PKCS1_SHA384,
      SSL_SIGN_ECDSA_SECP384R1_SHA384,
  
      SSL_SIGN_RSA_PKCS1_SHA256,
      SSL_SIGN_ECDSA_SECP256R1_SHA256,
  
      SSL_SIGN_RSA_PKCS1_SHA1,
      SSL_SIGN_ECDSA_SHA1,
  };
  
  static const uint16_t kDefaultTLS13SignatureAlgorithms[] = {
      SSL_SIGN_RSA_PSS_SHA512,
      SSL_SIGN_RSA_PKCS1_SHA512,
      SSL_SIGN_ECDSA_SECP521R1_SHA512,
  
      SSL_SIGN_RSA_PSS_SHA384,
      SSL_SIGN_RSA_PKCS1_SHA384,
      SSL_SIGN_ECDSA_SECP384R1_SHA384,
  
      SSL_SIGN_RSA_PSS_SHA256,
      SSL_SIGN_RSA_PKCS1_SHA256,
      SSL_SIGN_ECDSA_SECP256R1_SHA256,
  
      SSL_SIGN_RSA_PKCS1_SHA1,
      SSL_SIGN_ECDSA_SHA1,
  };
  
  size_t tls12_get_psigalgs(SSL *ssl, const uint16_t **psigs) {
    uint16_t min_version, max_version;
    if (!ssl_get_version_range(ssl, &min_version, &max_version)) {
      assert(0);  /* This should never happen. */
  
      /* Return an empty list. */
      ERR_clear_error();
      *psigs = NULL;
      return 0;
    }
  
    if (max_version >= TLS1_3_VERSION) {
      *psigs = kDefaultTLS13SignatureAlgorithms;
      return OPENSSL_ARRAY_SIZE(kDefaultTLS13SignatureAlgorithms);
    }
  
    *psigs = kDefaultSignatureAlgorithms;
    return OPENSSL_ARRAY_SIZE(kDefaultSignatureAlgorithms);
  }
  
  int tls12_check_peer_sigalg(SSL *ssl, int *out_alert, uint16_t sigalg) {
    const uint16_t *sent_sigs;
    size_t sent_sigslen, i;
  
    /* Check signature matches a type we sent */
    sent_sigslen = tls12_get_psigalgs(ssl, &sent_sigs);
    for (i = 0; i < sent_sigslen; i++) {
      if (sigalg == sent_sigs[i]) {
        break;
      }
    }
  
    if (i == sent_sigslen) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_SIGNATURE_TYPE);
      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
      return 0;
    }
  
    return 1;
  }
  
  /* Get a mask of disabled algorithms: an algorithm is disabled if it isn't
   * supported or doesn't appear in supported signature algorithms. Unlike
   * ssl_cipher_get_disabled this applies to a specific session and not global
   * settings. */
  void ssl_set_client_disabled(SSL *ssl) {
    CERT *c = ssl->cert;
    int have_rsa = 0, have_ecdsa = 0;
    c->mask_a = 0;
    c->mask_k = 0;
  
    /* Now go through all signature algorithms seeing if we support any for RSA,
     * DSA, ECDSA. Do this for all versions not just TLS 1.2. */
    const uint16_t *sigalgs;
    size_t num_sigalgs = tls12_get_psigalgs(ssl, &sigalgs);
    for (size_t i = 0; i < num_sigalgs; i++) {
      switch (sigalgs[i]) {
        case SSL_SIGN_RSA_PSS_SHA512:
        case SSL_SIGN_RSA_PSS_SHA384:
        case SSL_SIGN_RSA_PSS_SHA256:
        case SSL_SIGN_RSA_PKCS1_SHA512:
        case SSL_SIGN_RSA_PKCS1_SHA384:
        case SSL_SIGN_RSA_PKCS1_SHA256:
        case SSL_SIGN_RSA_PKCS1_SHA1:
          have_rsa = 1;
          break;
  
        case SSL_SIGN_ECDSA_SECP521R1_SHA512:
        case SSL_SIGN_ECDSA_SECP384R1_SHA384:
        case SSL_SIGN_ECDSA_SECP256R1_SHA256:
        case SSL_SIGN_ECDSA_SHA1:
          have_ecdsa = 1;
          break;
      }
    }
  
    /* Disable auth if we don't include any appropriate signature algorithms. */
    if (!have_rsa) {
      c->mask_a |= SSL_aRSA;
    }
    if (!have_ecdsa) {
      c->mask_a |= SSL_aECDSA;
    }
  
    /* with PSK there must be client callback set */
    if (!ssl->psk_client_callback) {
      c->mask_a |= SSL_aPSK;
      c->mask_k |= SSL_kPSK;
    }
  }
  
  /* tls_extension represents a TLS extension that is handled internally. The
   * |init| function is called for each handshake, before any other functions of
   * the extension. Then the add and parse callbacks are called as needed.
   *
   * The parse callbacks receive a |CBS| that contains the contents of the
   * extension (i.e. not including the type and length bytes). If an extension is
   * not received then the parse callbacks will be called with a NULL CBS so that
   * they can do any processing needed to handle the absence of an extension.
   *
   * The add callbacks receive a |CBB| to which the extension can be appended but
   * the function is responsible for appending the type and length bytes too.
   *
   * All callbacks return one for success and zero for error. If a parse function
   * returns zero then a fatal alert with value |*out_alert| will be sent. If
   * |*out_alert| isn't set, then a |decode_error| alert will be sent. */
  struct tls_extension {
    uint16_t value;
    void (*init)(SSL *ssl);
  
    int (*add_clienthello)(SSL *ssl, CBB *out);
    int (*parse_serverhello)(SSL *ssl, uint8_t *out_alert, CBS *contents);
  
    int (*parse_clienthello)(SSL *ssl, uint8_t *out_alert, CBS *contents);
    int (*add_serverhello)(SSL *ssl, CBB *out);
  };
  
  static int forbid_parse_serverhello(SSL *ssl, uint8_t *out_alert, CBS *contents) {
    if (contents != NULL) {
      /* Servers MUST NOT send this extension. */
      *out_alert = SSL_AD_UNSUPPORTED_EXTENSION;
      OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_EXTENSION);
      return 0;
    }
  
    return 1;
  }
  
  static int ignore_parse_clienthello(SSL *ssl, uint8_t *out_alert, CBS *contents) {
    /* This extension from the client is handled elsewhere. */
    return 1;
  }
  
  static int dont_add_serverhello(SSL *ssl, CBB *out) {
    return 1;
  }
  
  /* Server name indication (SNI).
   *
   * https://tools.ietf.org/html/rfc6066#section-3. */
  
  static void ext_sni_init(SSL *ssl) {
    ssl->s3->tmp.should_ack_sni = 0;
  }
  
  static int ext_sni_add_clienthello(SSL *ssl, CBB *out) {
    if (ssl->tlsext_hostname == NULL) {
      return 1;
    }
  
    CBB contents, server_name_list, name;
    if (!CBB_add_u16(out, TLSEXT_TYPE_server_name) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u16_length_prefixed(&contents, &server_name_list) ||
        !CBB_add_u8(&server_name_list, TLSEXT_NAMETYPE_host_name) ||
        !CBB_add_u16_length_prefixed(&server_name_list, &name) ||
        !CBB_add_bytes(&name, (const uint8_t *)ssl->tlsext_hostname,
                       strlen(ssl->tlsext_hostname)) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_sni_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                       CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    if (CBS_len(contents) != 0) {
      return 0;
    }
  
    assert(ssl->tlsext_hostname != NULL);
  
    if (ssl->session == NULL) {
      assert(ssl->s3->new_session->tlsext_hostname == NULL);
      ssl->s3->new_session->tlsext_hostname = BUF_strdup(ssl->tlsext_hostname);
      if (!ssl->s3->new_session->tlsext_hostname) {
        *out_alert = SSL_AD_INTERNAL_ERROR;
        return 0;
      }
    }
  
    return 1;
  }
  
  static int ext_sni_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                       CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    CBS server_name_list, host_name;
    uint8_t name_type;
    if (!CBS_get_u16_length_prefixed(contents, &server_name_list) ||
        !CBS_get_u8(&server_name_list, &name_type) ||
        /* Although the server_name extension was intended to be extensible to
         * new name types and multiple names, OpenSSL 1.0.x had a bug which meant
         * different name types will cause an error. Further, RFC 4366 originally
         * defined syntax inextensibly. RFC 6066 corrected this mistake, but
         * adding new name types is no longer feasible.
         *
         * Act as if the extensibility does not exist to simplify parsing. */
        !CBS_get_u16_length_prefixed(&server_name_list, &host_name) ||
        CBS_len(&server_name_list) != 0 ||
        CBS_len(contents) != 0) {
      return 0;
    }
  
    if (name_type != TLSEXT_NAMETYPE_host_name ||
        CBS_len(&host_name) == 0 ||
        CBS_len(&host_name) > TLSEXT_MAXLEN_host_name ||
        CBS_contains_zero_byte(&host_name)) {
      *out_alert = SSL_AD_UNRECOGNIZED_NAME;
      return 0;
    }
  
    /* TODO(davidben): SNI should be resolved before resumption. We have the
     * early callback as a replacement, but we should fix the current callback
     * and avoid the need for |SSL_CTX_set_session_id_context|. */
    if (ssl->session == NULL) {
      assert(ssl->s3->new_session->tlsext_hostname == NULL);
  
      /* Copy the hostname as a string. */
      if (!CBS_strdup(&host_name, &ssl->s3->new_session->tlsext_hostname)) {
        *out_alert = SSL_AD_INTERNAL_ERROR;
        return 0;
      }
  
      ssl->s3->tmp.should_ack_sni = 1;
    }
  
    return 1;
  }
  
  static int ext_sni_add_serverhello(SSL *ssl, CBB *out) {
    if (ssl->session != NULL ||
        !ssl->s3->tmp.should_ack_sni ||
        ssl->s3->new_session->tlsext_hostname == NULL) {
      return 1;
    }
  
    if (!CBB_add_u16(out, TLSEXT_TYPE_server_name) ||
        !CBB_add_u16(out, 0 /* length */)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* Renegotiation indication.
   *
   * https://tools.ietf.org/html/rfc5746 */
  
  static int ext_ri_add_clienthello(SSL *ssl, CBB *out) {
    uint16_t min_version, max_version;
    if (!ssl_get_version_range(ssl, &min_version, &max_version)) {
      return 0;
    }
  
    /* Renegotiation indication is not necessary in TLS 1.3. */
    if (min_version >= TLS1_3_VERSION) {
      return 1;
    }
  
    CBB contents, prev_finished;
    if (!CBB_add_u16(out, TLSEXT_TYPE_renegotiate) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u8_length_prefixed(&contents, &prev_finished) ||
        !CBB_add_bytes(&prev_finished, ssl->s3->previous_client_finished,
                       ssl->s3->previous_client_finished_len) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_ri_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                      CBS *contents) {
    if (contents != NULL && ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 0;
    }
  
    /* Servers may not switch between omitting the extension and supporting it.
     * See RFC 5746, sections 3.5 and 4.2. */
    if (ssl->s3->initial_handshake_complete &&
        (contents != NULL) != ssl->s3->send_connection_binding) {
      *out_alert = SSL_AD_HANDSHAKE_FAILURE;
      OPENSSL_PUT_ERROR(SSL, SSL_R_RENEGOTIATION_MISMATCH);
      return 0;
    }
  
    if (contents == NULL) {
      /* Strictly speaking, if we want to avoid an attack we should *always* see
       * RI even on initial ServerHello because the client doesn't see any
       * renegotiation during an attack. However this would mean we could not
       * connect to any server which doesn't support RI.
       *
       * OpenSSL has |SSL_OP_LEGACY_SERVER_CONNECT| to control this, but in
       * practical terms every client sets it so it's just assumed here. */
      return 1;
    }
  
    const size_t expected_len = ssl->s3->previous_client_finished_len +
                                ssl->s3->previous_server_finished_len;
  
    /* Check for logic errors */
    assert(!expected_len || ssl->s3->previous_client_finished_len);
    assert(!expected_len || ssl->s3->previous_server_finished_len);
  
    /* Parse out the extension contents. */
    CBS renegotiated_connection;
    if (!CBS_get_u8_length_prefixed(contents, &renegotiated_connection) ||
        CBS_len(contents) != 0) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_RENEGOTIATION_ENCODING_ERR);
      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
      return 0;
    }
  
    /* Check that the extension matches. */
    if (CBS_len(&renegotiated_connection) != expected_len) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_RENEGOTIATION_MISMATCH);
      *out_alert = SSL_AD_HANDSHAKE_FAILURE;
      return 0;
    }
  
    const uint8_t *d = CBS_data(&renegotiated_connection);
    if (CRYPTO_memcmp(d, ssl->s3->previous_client_finished,
          ssl->s3->previous_client_finished_len)) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_RENEGOTIATION_MISMATCH);
      *out_alert = SSL_AD_HANDSHAKE_FAILURE;
      return 0;
    }
    d += ssl->s3->previous_client_finished_len;
  
    if (CRYPTO_memcmp(d, ssl->s3->previous_server_finished,
          ssl->s3->previous_server_finished_len)) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_RENEGOTIATION_MISMATCH);
      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
      return 0;
    }
    ssl->s3->send_connection_binding = 1;
  
    return 1;
  }
  
  static int ext_ri_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                      CBS *contents) {
    /* Renegotiation isn't supported as a server so this function should never be
     * called after the initial handshake. */
    assert(!ssl->s3->initial_handshake_complete);
  
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 1;
    }
  
    if (contents == NULL) {
      return 1;
    }
  
    CBS renegotiated_connection;
    if (!CBS_get_u8_length_prefixed(contents, &renegotiated_connection) ||
        CBS_len(contents) != 0) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_RENEGOTIATION_ENCODING_ERR);
      return 0;
    }
  
    /* Check that the extension matches */
    if (!CBS_mem_equal(&renegotiated_connection,
                       ssl->s3->previous_client_finished,
                       ssl->s3->previous_client_finished_len)) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_RENEGOTIATION_MISMATCH);
      *out_alert = SSL_AD_HANDSHAKE_FAILURE;
      return 0;
    }
  
    ssl->s3->send_connection_binding = 1;
  
    return 1;
  }
  
  static int ext_ri_add_serverhello(SSL *ssl, CBB *out) {
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 1;
    }
  
    CBB contents, prev_finished;
    if (!CBB_add_u16(out, TLSEXT_TYPE_renegotiate) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u8_length_prefixed(&contents, &prev_finished) ||
        !CBB_add_bytes(&prev_finished, ssl->s3->previous_client_finished,
                       ssl->s3->previous_client_finished_len) ||
        !CBB_add_bytes(&prev_finished, ssl->s3->previous_server_finished,
                       ssl->s3->previous_server_finished_len) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* Extended Master Secret.
   *
   * https://tools.ietf.org/html/rfc7627 */
  
  static int ext_ems_add_clienthello(SSL *ssl, CBB *out) {
    uint16_t min_version, max_version;
    if (!ssl_get_version_range(ssl, &min_version, &max_version)) {
      return 0;
    }
  
    /* Extended master secret is not necessary in TLS 1.3. */
    if (min_version >= TLS1_3_VERSION || max_version <= SSL3_VERSION) {
      return 1;
    }
  
    if (!CBB_add_u16(out, TLSEXT_TYPE_extended_master_secret) ||
        !CBB_add_u16(out, 0 /* length */)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_ems_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                       CBS *contents) {
    /* Whether EMS is negotiated may not change on renegotation. */
    if (ssl->s3->initial_handshake_complete) {
      if ((contents != NULL) != ssl->s3->tmp.extended_master_secret) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_RENEGOTIATION_EMS_MISMATCH);
        *out_alert = SSL_AD_ILLEGAL_PARAMETER;
        return 0;
      }
  
      return 1;
    }
  
    if (contents == NULL) {
      return 1;
    }
  
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION ||
        ssl->version == SSL3_VERSION) {
      return 0;
    }
  
    if (CBS_len(contents) != 0) {
      return 0;
    }
  
    ssl->s3->tmp.extended_master_secret = 1;
    return 1;
  }
  
  static int ext_ems_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                       CBS *contents) {
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION ||
        ssl->version == SSL3_VERSION) {
      return 1;
    }
  
    if (contents == NULL) {
      return 1;
    }
  
    if (CBS_len(contents) != 0) {
      return 0;
    }
  
    ssl->s3->tmp.extended_master_secret = 1;
    return 1;
  }
  
  static int ext_ems_add_serverhello(SSL *ssl, CBB *out) {
    if (!ssl->s3->tmp.extended_master_secret) {
      return 1;
    }
  
    if (!CBB_add_u16(out, TLSEXT_TYPE_extended_master_secret) ||
        !CBB_add_u16(out, 0 /* length */)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* Session tickets.
   *
   * https://tools.ietf.org/html/rfc5077 */
  
  static int ext_ticket_add_clienthello(SSL *ssl, CBB *out) {
    uint16_t min_version, max_version;
    if (!ssl_get_version_range(ssl, &min_version, &max_version)) {
      return 0;
    }
  
    /* TLS 1.3 uses a different ticket extension. */
    if (min_version >= TLS1_3_VERSION ||
        SSL_get_options(ssl) & SSL_OP_NO_TICKET) {
      return 1;
    }
  
    const uint8_t *ticket_data = NULL;
    int ticket_len = 0;
  
    /* Renegotiation does not participate in session resumption. However, still
     * advertise the extension to avoid potentially breaking servers which carry
     * over the state from the previous handshake, such as OpenSSL servers
     * without upstream's 3c3f0259238594d77264a78944d409f2127642c4. */
    uint16_t session_version;
    if (!ssl->s3->initial_handshake_complete &&
        ssl->session != NULL &&
        ssl->session->tlsext_tick != NULL &&
        /* Don't send TLS 1.3 session tickets in the ticket extension. */
        ssl->method->version_from_wire(&session_version,
                                       ssl->session->ssl_version) &&
        session_version < TLS1_3_VERSION) {
      ticket_data = ssl->session->tlsext_tick;
      ticket_len = ssl->session->tlsext_ticklen;
    }
  
    CBB ticket;
    if (!CBB_add_u16(out, TLSEXT_TYPE_session_ticket) ||
        !CBB_add_u16_length_prefixed(out, &ticket) ||
        !CBB_add_bytes(&ticket, ticket_data, ticket_len) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_ticket_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                          CBS *contents) {
    ssl->tlsext_ticket_expected = 0;
  
    if (contents == NULL) {
      return 1;
    }
  
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 0;
    }
  
    /* If |SSL_OP_NO_TICKET| is set then no extension will have been sent and
     * this function should never be called, even if the server tries to send the
     * extension. */
    assert((SSL_get_options(ssl) & SSL_OP_NO_TICKET) == 0);
  
    if (CBS_len(contents) != 0) {
      return 0;
    }
  
    ssl->tlsext_ticket_expected = 1;
    return 1;
  }
  
  static int ext_ticket_add_serverhello(SSL *ssl, CBB *out) {
    if (!ssl->tlsext_ticket_expected) {
      return 1;
    }
  
    /* If |SSL_OP_NO_TICKET| is set, |tlsext_ticket_expected| should never be
     * true. */
    assert((SSL_get_options(ssl) & SSL_OP_NO_TICKET) == 0);
  
    if (!CBB_add_u16(out, TLSEXT_TYPE_session_ticket) ||
        !CBB_add_u16(out, 0 /* length */)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* Signature Algorithms.
   *
   * https://tools.ietf.org/html/rfc5246#section-7.4.1.4.1 */
  
  static int ext_sigalgs_add_clienthello(SSL *ssl, CBB *out) {
    uint16_t min_version, max_version;
    if (!ssl_get_version_range(ssl, &min_version, &max_version)) {
      return 0;
    }
  
    if (max_version < TLS1_2_VERSION) {
      return 1;
    }
  
    const uint16_t *sigalgs;
    const size_t num_sigalgs = tls12_get_psigalgs(ssl, &sigalgs);
  
    CBB contents, sigalgs_cbb;
    if (!CBB_add_u16(out, TLSEXT_TYPE_signature_algorithms) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u16_length_prefixed(&contents, &sigalgs_cbb)) {
      return 0;
    }
  
    for (size_t i = 0; i < num_sigalgs; i++) {
      if (!CBB_add_u16(&sigalgs_cbb, sigalgs[i])) {
        return 0;
      }
    }
  
    if (!CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_sigalgs_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                           CBS *contents) {
    OPENSSL_free(ssl->s3->hs->peer_sigalgs);
    ssl->s3->hs->peer_sigalgs = NULL;
    ssl->s3->hs->num_peer_sigalgs = 0;
  
    if (contents == NULL) {
      return 1;
    }
  
    CBS supported_signature_algorithms;
    if (!CBS_get_u16_length_prefixed(contents, &supported_signature_algorithms) ||
        CBS_len(contents) != 0 ||
        CBS_len(&supported_signature_algorithms) == 0 ||
        !tls1_parse_peer_sigalgs(ssl, &supported_signature_algorithms)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* OCSP Stapling.
   *
   * https://tools.ietf.org/html/rfc6066#section-8 */
  
  static void ext_ocsp_init(SSL *ssl) {
    ssl->s3->tmp.certificate_status_expected = 0;
    ssl->tlsext_status_type = -1;
  }
  
  static int ext_ocsp_add_clienthello(SSL *ssl, CBB *out) {
    if (!ssl->ocsp_stapling_enabled) {
      return 1;
    }
  
    CBB contents;
    if (!CBB_add_u16(out, TLSEXT_TYPE_status_request) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u8(&contents, TLSEXT_STATUSTYPE_ocsp) ||
        !CBB_add_u16(&contents, 0 /* empty responder ID list */) ||
        !CBB_add_u16(&contents, 0 /* empty request extensions */) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    ssl->tlsext_status_type = TLSEXT_STATUSTYPE_ocsp;
    return 1;
  }
  
  static int ext_ocsp_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                        CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    /* OCSP stapling is forbidden on a non-certificate cipher. */
    if (!ssl_cipher_uses_certificate_auth(ssl->s3->tmp.new_cipher)) {
      return 0;
    }
  
    if (ssl3_protocol_version(ssl) < TLS1_3_VERSION) {
      if (CBS_len(contents) != 0) {
        return 0;
      }
  
      ssl->s3->tmp.certificate_status_expected = 1;
      return 1;
    }
  
    uint8_t status_type;
    CBS ocsp_response;
    if (!CBS_get_u8(contents, &status_type) ||
        status_type != TLSEXT_STATUSTYPE_ocsp ||
        !CBS_get_u24_length_prefixed(contents, &ocsp_response) ||
        CBS_len(&ocsp_response) == 0 ||
        CBS_len(contents) != 0) {
      return 0;
    }
  
    if (!CBS_stow(&ocsp_response, &ssl->s3->new_session->ocsp_response,
                  &ssl->s3->new_session->ocsp_response_length)) {
      *out_alert = SSL_AD_INTERNAL_ERROR;
      return 0;
    }
  
    return 1;
  }
  
  static int ext_ocsp_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                        CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    uint8_t status_type;
    if (!CBS_get_u8(contents, &status_type)) {
      return 0;
    }
  
    /* We cannot decide whether OCSP stapling will occur yet because the correct
     * SSL_CTX might not have been selected. */
    ssl->s3->tmp.ocsp_stapling_requested = status_type == TLSEXT_STATUSTYPE_ocsp;
  
    return 1;
  }
  
  static int ext_ocsp_add_serverhello(SSL *ssl, CBB *out) {
    if (!ssl->s3->tmp.ocsp_stapling_requested ||
        ssl->ctx->ocsp_response_length == 0 ||
        !ssl_cipher_uses_certificate_auth(ssl->s3->tmp.new_cipher)) {
      return 1;
    }
  
    if (ssl3_protocol_version(ssl) < TLS1_3_VERSION) {
      /* The extension shouldn't be sent when resuming sessions. */
      if (ssl->session != NULL) {
        return 1;
      }
  
      ssl->s3->tmp.certificate_status_expected = 1;
  
      return CBB_add_u16(out, TLSEXT_TYPE_status_request) &&
             CBB_add_u16(out, 0 /* length */);
    }
  
    CBB body, ocsp_response;
    return CBB_add_u16(out, TLSEXT_TYPE_status_request) &&
           CBB_add_u16_length_prefixed(out, &body) &&
           CBB_add_u8(&body, TLSEXT_STATUSTYPE_ocsp) &&
           CBB_add_u24_length_prefixed(&body, &ocsp_response) &&
           CBB_add_bytes(&ocsp_response, ssl->ctx->ocsp_response,
                         ssl->ctx->ocsp_response_length) &&
           CBB_flush(out);
  }
  
  
  /* Next protocol negotiation.
   *
   * https://htmlpreview.github.io/?https://github.com/agl/technotes/blob/master/nextprotoneg.html */
  
  static void ext_npn_init(SSL *ssl) {
    ssl->s3->next_proto_neg_seen = 0;
  }
  
  static int ext_npn_add_clienthello(SSL *ssl, CBB *out) {
    if (ssl->s3->initial_handshake_complete ||
        ssl->ctx->next_proto_select_cb == NULL ||
        (ssl->options & SSL_OP_DISABLE_NPN) ||
        SSL_is_dtls(ssl)) {
      return 1;
    }
  
    if (!CBB_add_u16(out, TLSEXT_TYPE_next_proto_neg) ||
        !CBB_add_u16(out, 0 /* length */)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_npn_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                       CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 0;
    }
  
    /* If any of these are false then we should never have sent the NPN
     * extension in the ClientHello and thus this function should never have been
     * called. */
    assert(!ssl->s3->initial_handshake_complete);
    assert(!SSL_is_dtls(ssl));
    assert(ssl->ctx->next_proto_select_cb != NULL);
    assert(!(ssl->options & SSL_OP_DISABLE_NPN));
  
    if (ssl->s3->alpn_selected != NULL) {
      /* NPN and ALPN may not be negotiated in the same connection. */
      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
      OPENSSL_PUT_ERROR(SSL, SSL_R_NEGOTIATED_BOTH_NPN_AND_ALPN);
      return 0;
    }
  
    const uint8_t *const orig_contents = CBS_data(contents);
    const size_t orig_len = CBS_len(contents);
  
    while (CBS_len(contents) != 0) {
      CBS proto;
      if (!CBS_get_u8_length_prefixed(contents, &proto) ||
          CBS_len(&proto) == 0) {
        return 0;
      }
    }
  
    uint8_t *selected;
    uint8_t selected_len;
    if (ssl->ctx->next_proto_select_cb(
            ssl, &selected, &selected_len, orig_contents, orig_len,
            ssl->ctx->next_proto_select_cb_arg) != SSL_TLSEXT_ERR_OK) {
      *out_alert = SSL_AD_INTERNAL_ERROR;
      return 0;
    }
  
    OPENSSL_free(ssl->s3->next_proto_negotiated);
    ssl->s3->next_proto_negotiated = BUF_memdup(selected, selected_len);
    if (ssl->s3->next_proto_negotiated == NULL) {
      *out_alert = SSL_AD_INTERNAL_ERROR;
      return 0;
    }
  
    ssl->s3->next_proto_negotiated_len = selected_len;
    ssl->s3->next_proto_neg_seen = 1;
  
    return 1;
  }
  
  static int ext_npn_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                       CBS *contents) {
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 1;
    }
  
    if (contents != NULL && CBS_len(contents) != 0) {
      return 0;
    }
  
    if (contents == NULL ||
        ssl->s3->initial_handshake_complete ||
        /* If the ALPN extension is seen before NPN, ignore it. (If ALPN is seen
         * afterwards, parsing the ALPN extension will clear
         * |next_proto_neg_seen|. */
        ssl->s3->alpn_selected != NULL ||
        ssl->ctx->next_protos_advertised_cb == NULL ||
        SSL_is_dtls(ssl)) {
      return 1;
    }
  
    ssl->s3->next_proto_neg_seen = 1;
    return 1;
  }
  
  static int ext_npn_add_serverhello(SSL *ssl, CBB *out) {
    /* |next_proto_neg_seen| might have been cleared when an ALPN extension was
     * parsed. */
    if (!ssl->s3->next_proto_neg_seen) {
      return 1;
    }
  
    const uint8_t *npa;
    unsigned npa_len;
  
    if (ssl->ctx->next_protos_advertised_cb(
            ssl, &npa, &npa_len, ssl->ctx->next_protos_advertised_cb_arg) !=
        SSL_TLSEXT_ERR_OK) {
      ssl->s3->next_proto_neg_seen = 0;
      return 1;
    }
  
    CBB contents;
    if (!CBB_add_u16(out, TLSEXT_TYPE_next_proto_neg) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_bytes(&contents, npa, npa_len) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* Signed certificate timestamps.
   *
   * https://tools.ietf.org/html/rfc6962#section-3.3.1 */
  
  static int ext_sct_add_clienthello(SSL *ssl, CBB *out) {
    if (!ssl->signed_cert_timestamps_enabled) {
      return 1;
    }
  
    if (!CBB_add_u16(out, TLSEXT_TYPE_certificate_timestamp) ||
        !CBB_add_u16(out, 0 /* length */)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_sct_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                       CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    /* If this is false then we should never have sent the SCT extension in the
     * ClientHello and thus this function should never have been called. */
    assert(ssl->signed_cert_timestamps_enabled);
  
    if (CBS_len(contents) == 0) {
      *out_alert = SSL_AD_DECODE_ERROR;
      return 0;
    }
  
    /* Session resumption uses the original session information. */
    if (!ssl->s3->session_reused &&
        !CBS_stow(
            contents,
            &ssl->s3->new_session->tlsext_signed_cert_timestamp_list,
            &ssl->s3->new_session->tlsext_signed_cert_timestamp_list_length)) {
      *out_alert = SSL_AD_INTERNAL_ERROR;
      return 0;
    }
  
    return 1;
  }
  
  static int ext_sct_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                       CBS *contents) {
    return contents == NULL || CBS_len(contents) == 0;
  }
  
  static int ext_sct_add_serverhello(SSL *ssl, CBB *out) {
    /* The extension shouldn't be sent when resuming sessions. */
    if (ssl->s3->session_reused ||
        ssl->ctx->signed_cert_timestamp_list_length == 0) {
      return 1;
    }
  
    CBB contents;
    return CBB_add_u16(out, TLSEXT_TYPE_certificate_timestamp) &&
           CBB_add_u16_length_prefixed(out, &contents) &&
           CBB_add_bytes(&contents, ssl->ctx->signed_cert_timestamp_list,
                         ssl->ctx->signed_cert_timestamp_list_length) &&
           CBB_flush(out);
  }
  
  
  /* Application-level Protocol Negotiation.
   *
   * https://tools.ietf.org/html/rfc7301 */
  
  static void ext_alpn_init(SSL *ssl) {
    OPENSSL_free(ssl->s3->alpn_selected);
    ssl->s3->alpn_selected = NULL;
  }
  
  static int ext_alpn_add_clienthello(SSL *ssl, CBB *out) {
    if (ssl->alpn_client_proto_list == NULL ||
        ssl->s3->initial_handshake_complete) {
      return 1;
    }
  
    CBB contents, proto_list;
    if (!CBB_add_u16(out, TLSEXT_TYPE_application_layer_protocol_negotiation) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u16_length_prefixed(&contents, &proto_list) ||
        !CBB_add_bytes(&proto_list, ssl->alpn_client_proto_list,
                       ssl->alpn_client_proto_list_len) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_alpn_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                        CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    assert(!ssl->s3->initial_handshake_complete);
    assert(ssl->alpn_client_proto_list != NULL);
  
    if (ssl->s3->next_proto_neg_seen) {
      /* NPN and ALPN may not be negotiated in the same connection. */
      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
      OPENSSL_PUT_ERROR(SSL, SSL_R_NEGOTIATED_BOTH_NPN_AND_ALPN);
      return 0;
    }
  
    /* The extension data consists of a ProtocolNameList which must have
     * exactly one ProtocolName. Each of these is length-prefixed. */
    CBS protocol_name_list, protocol_name;
    if (!CBS_get_u16_length_prefixed(contents, &protocol_name_list) ||
        CBS_len(contents) != 0 ||
        !CBS_get_u8_length_prefixed(&protocol_name_list, &protocol_name) ||
        /* Empty protocol names are forbidden. */
        CBS_len(&protocol_name) == 0 ||
        CBS_len(&protocol_name_list) != 0) {
      return 0;
    }
  
    /* Check that the protcol name is one of the ones we advertised. */
    int protocol_ok = 0;
    CBS client_protocol_name_list, client_protocol_name;
    CBS_init(&client_protocol_name_list, ssl->alpn_client_proto_list,
             ssl->alpn_client_proto_list_len);
    while (CBS_len(&client_protocol_name_list) > 0) {
      if (!CBS_get_u8_length_prefixed(&client_protocol_name_list,
                                      &client_protocol_name)) {
        *out_alert = SSL_AD_INTERNAL_ERROR;
        return 0;
      }
  
      if (CBS_len(&client_protocol_name) == CBS_len(&protocol_name) &&
          memcmp(CBS_data(&client_protocol_name), CBS_data(&protocol_name),
                 CBS_len(&protocol_name)) == 0) {
        protocol_ok = 1;
        break;
      }
    }
  
    if (!protocol_ok) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_ALPN_PROTOCOL);
      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
      return 0;
    }
  
    if (!CBS_stow(&protocol_name, &ssl->s3->alpn_selected,
                  &ssl->s3->alpn_selected_len)) {
      *out_alert = SSL_AD_INTERNAL_ERROR;
      return 0;
    }
  
    return 1;
  }
  
  static int ext_alpn_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                        CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    if (ssl->ctx->alpn_select_cb == NULL ||
        ssl->s3->initial_handshake_complete) {
      return 1;
    }
  
    /* ALPN takes precedence over NPN. */
    ssl->s3->next_proto_neg_seen = 0;
  
    CBS protocol_name_list;
    if (!CBS_get_u16_length_prefixed(contents, &protocol_name_list) ||
        CBS_len(contents) != 0 ||
        CBS_len(&protocol_name_list) < 2) {
      return 0;
    }
  
    /* Validate the protocol list. */
    CBS protocol_name_list_copy = protocol_name_list;
    while (CBS_len(&protocol_name_list_copy) > 0) {
      CBS protocol_name;
  
      if (!CBS_get_u8_length_prefixed(&protocol_name_list_copy, &protocol_name) ||
          /* Empty protocol names are forbidden. */
          CBS_len(&protocol_name) == 0) {
        return 0;
      }
    }
  
    const uint8_t *selected;
    uint8_t selected_len;
    if (ssl->ctx->alpn_select_cb(
            ssl, &selected, &selected_len, CBS_data(&protocol_name_list),
            CBS_len(&protocol_name_list),
            ssl->ctx->alpn_select_cb_arg) == SSL_TLSEXT_ERR_OK) {
      OPENSSL_free(ssl->s3->alpn_selected);
      ssl->s3->alpn_selected = BUF_memdup(selected, selected_len);
      if (ssl->s3->alpn_selected == NULL) {
        *out_alert = SSL_AD_INTERNAL_ERROR;
        return 0;
      }
      ssl->s3->alpn_selected_len = selected_len;
    }
  
    return 1;
  }
  
  static int ext_alpn_add_serverhello(SSL *ssl, CBB *out) {
    if (ssl->s3->alpn_selected == NULL) {
      return 1;
    }
  
    CBB contents, proto_list, proto;
    if (!CBB_add_u16(out, TLSEXT_TYPE_application_layer_protocol_negotiation) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u16_length_prefixed(&contents, &proto_list) ||
        !CBB_add_u8_length_prefixed(&proto_list, &proto) ||
        !CBB_add_bytes(&proto, ssl->s3->alpn_selected,
                       ssl->s3->alpn_selected_len) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* Channel ID.
   *
   * https://tools.ietf.org/html/draft-balfanz-tls-channelid-01 */
  
  static void ext_channel_id_init(SSL *ssl) {
    ssl->s3->tlsext_channel_id_valid = 0;
  }
  
  static int ext_channel_id_add_clienthello(SSL *ssl, CBB *out) {
    if (!ssl->tlsext_channel_id_enabled ||
        SSL_is_dtls(ssl)) {
      return 1;
    }
  
    if (!CBB_add_u16(out, TLSEXT_TYPE_channel_id) ||
        !CBB_add_u16(out, 0 /* length */)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_channel_id_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                              CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 0;
    }
  
    assert(!SSL_is_dtls(ssl));
    assert(ssl->tlsext_channel_id_enabled);
  
    if (CBS_len(contents) != 0) {
      return 0;
    }
  
    ssl->s3->tlsext_channel_id_valid = 1;
    return 1;
  }
  
  static int ext_channel_id_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                              CBS *contents) {
    if (contents == NULL ||
        !ssl->tlsext_channel_id_enabled ||
        SSL_is_dtls(ssl)) {
      return 1;
    }
  
    if (CBS_len(contents) != 0) {
      return 0;
    }
  
    ssl->s3->tlsext_channel_id_valid = 1;
    return 1;
  }
  
  static int ext_channel_id_add_serverhello(SSL *ssl, CBB *out) {
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 1;
    }
  
    if (!ssl->s3->tlsext_channel_id_valid) {
      return 1;
    }
  
    if (!CBB_add_u16(out, TLSEXT_TYPE_channel_id) ||
        !CBB_add_u16(out, 0 /* length */)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* Secure Real-time Transport Protocol (SRTP) extension.
   *
   * https://tools.ietf.org/html/rfc5764 */
  
  
  static void ext_srtp_init(SSL *ssl) {
    ssl->srtp_profile = NULL;
  }
  
  static int ext_srtp_add_clienthello(SSL *ssl, CBB *out) {
    STACK_OF(SRTP_PROTECTION_PROFILE) *profiles = SSL_get_srtp_profiles(ssl);
    if (profiles == NULL) {
      return 1;
    }
    const size_t num_profiles = sk_SRTP_PROTECTION_PROFILE_num(profiles);
    if (num_profiles == 0) {
      return 1;
    }
  
    CBB contents, profile_ids;
    if (!CBB_add_u16(out, TLSEXT_TYPE_srtp) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u16_length_prefixed(&contents, &profile_ids)) {
      return 0;
    }
  
    for (size_t i = 0; i < num_profiles; i++) {
      if (!CBB_add_u16(&profile_ids,
                       sk_SRTP_PROTECTION_PROFILE_value(profiles, i)->id)) {
        return 0;
      }
    }
  
    if (!CBB_add_u8(&contents, 0 /* empty use_mki value */) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_srtp_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                        CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    /* The extension consists of a u16-prefixed profile ID list containing a
     * single uint16_t profile ID, then followed by a u8-prefixed srtp_mki field.
     *
     * See https://tools.ietf.org/html/rfc5764#section-4.1.1 */
    CBS profile_ids, srtp_mki;
    uint16_t profile_id;
    if (!CBS_get_u16_length_prefixed(contents, &profile_ids) ||
        !CBS_get_u16(&profile_ids, &profile_id) ||
        CBS_len(&profile_ids) != 0 ||
        !CBS_get_u8_length_prefixed(contents, &srtp_mki) ||
        CBS_len(contents) != 0) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_BAD_SRTP_PROTECTION_PROFILE_LIST);
      return 0;
    }
  
    if (CBS_len(&srtp_mki) != 0) {
      /* Must be no MKI, since we never offer one. */
      OPENSSL_PUT_ERROR(SSL, SSL_R_BAD_SRTP_MKI_VALUE);
      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
      return 0;
    }
  
    STACK_OF(SRTP_PROTECTION_PROFILE) *profiles = SSL_get_srtp_profiles(ssl);
  
    /* Check to see if the server gave us something we support (and presumably
     * offered). */
    for (size_t i = 0; i < sk_SRTP_PROTECTION_PROFILE_num(profiles); i++) {
      const SRTP_PROTECTION_PROFILE *profile =
          sk_SRTP_PROTECTION_PROFILE_value(profiles, i);
  
      if (profile->id == profile_id) {
        ssl->srtp_profile = profile;
        return 1;
      }
    }
  
    OPENSSL_PUT_ERROR(SSL, SSL_R_BAD_SRTP_PROTECTION_PROFILE_LIST);
    *out_alert = SSL_AD_ILLEGAL_PARAMETER;
    return 0;
  }
  
  static int ext_srtp_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                        CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    CBS profile_ids, srtp_mki;
    if (!CBS_get_u16_length_prefixed(contents, &profile_ids) ||
        CBS_len(&profile_ids) < 2 ||
        !CBS_get_u8_length_prefixed(contents, &srtp_mki) ||
        CBS_len(contents) != 0) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_BAD_SRTP_PROTECTION_PROFILE_LIST);
      return 0;
    }
    /* Discard the MKI value for now. */
  
    const STACK_OF(SRTP_PROTECTION_PROFILE) *server_profiles =
        SSL_get_srtp_profiles(ssl);
  
    /* Pick the server's most preferred profile. */
    for (size_t i = 0; i < sk_SRTP_PROTECTION_PROFILE_num(server_profiles); i++) {
      const SRTP_PROTECTION_PROFILE *server_profile =
          sk_SRTP_PROTECTION_PROFILE_value(server_profiles, i);
  
      CBS profile_ids_tmp;
      CBS_init(&profile_ids_tmp, CBS_data(&profile_ids), CBS_len(&profile_ids));
  
      while (CBS_len(&profile_ids_tmp) > 0) {
        uint16_t profile_id;
        if (!CBS_get_u16(&profile_ids_tmp, &profile_id)) {
          return 0;
        }
  
        if (server_profile->id == profile_id) {
          ssl->srtp_profile = server_profile;
          return 1;
        }
      }
    }
  
    return 1;
  }
  
  static int ext_srtp_add_serverhello(SSL *ssl, CBB *out) {
    if (ssl->srtp_profile == NULL) {
      return 1;
    }
  
    CBB contents, profile_ids;
    if (!CBB_add_u16(out, TLSEXT_TYPE_srtp) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u16_length_prefixed(&contents, &profile_ids) ||
        !CBB_add_u16(&profile_ids, ssl->srtp_profile->id) ||
        !CBB_add_u8(&contents, 0 /* empty MKI */) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* EC point formats.
   *
   * https://tools.ietf.org/html/rfc4492#section-5.1.2 */
  
  static int ssl_any_ec_cipher_suites_enabled(const SSL *ssl) {
    if (ssl->version < TLS1_VERSION && !SSL_is_dtls(ssl)) {
      return 0;
    }
  
    const STACK_OF(SSL_CIPHER) *cipher_stack = SSL_get_ciphers(ssl);
  
    for (size_t i = 0; i < sk_SSL_CIPHER_num(cipher_stack); i++) {
      const SSL_CIPHER *cipher = sk_SSL_CIPHER_value(cipher_stack, i);
  
      const uint32_t alg_k = cipher->algorithm_mkey;
      const uint32_t alg_a = cipher->algorithm_auth;
      if ((alg_k & SSL_kECDHE) || (alg_a & SSL_aECDSA)) {
        return 1;
      }
    }
  
    return 0;
  }
  
  static int ext_ec_point_add_extension(SSL *ssl, CBB *out) {
    CBB contents, formats;
    if (!CBB_add_u16(out, TLSEXT_TYPE_ec_point_formats) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u8_length_prefixed(&contents, &formats) ||
        !CBB_add_u8(&formats, TLSEXT_ECPOINTFORMAT_uncompressed) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  static int ext_ec_point_add_clienthello(SSL *ssl, CBB *out) {
    if (!ssl_any_ec_cipher_suites_enabled(ssl)) {
      return 1;
    }
  
    return ext_ec_point_add_extension(ssl, out);
  }
  
  static int ext_ec_point_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                            CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 0;
    }
  
    CBS ec_point_format_list;
    if (!CBS_get_u8_length_prefixed(contents, &ec_point_format_list) ||
        CBS_len(contents) != 0) {
      return 0;
    }
  
    /* Per RFC 4492, section 5.1.2, implementations MUST support the uncompressed
     * point format. */
    if (memchr(CBS_data(&ec_point_format_list), TLSEXT_ECPOINTFORMAT_uncompressed,
               CBS_len(&ec_point_format_list)) == NULL) {
      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
      return 0;
    }
  
    return 1;
  }
  
  static int ext_ec_point_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                            CBS *contents) {
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 1;
    }
  
    return ext_ec_point_parse_serverhello(ssl, out_alert, contents);
  }
  
  static int ext_ec_point_add_serverhello(SSL *ssl, CBB *out) {
    if (ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
      return 1;
    }
  
    const uint32_t alg_k = ssl->s3->tmp.new_cipher->algorithm_mkey;
    const uint32_t alg_a = ssl->s3->tmp.new_cipher->algorithm_auth;
    const int using_ecc = (alg_k & SSL_kECDHE) || (alg_a & SSL_aECDSA);
  
    if (!using_ecc) {
      return 1;
    }
  
    return ext_ec_point_add_extension(ssl, out);
  }
  
  /* Pre Shared Key
   *
   * https://tools.ietf.org/html/draft-ietf-tls-tls13-14 */
  
  static int ext_pre_shared_key_add_clienthello(SSL *ssl, CBB *out) {
    uint16_t min_version, max_version;
    if (!ssl_get_version_range(ssl, &min_version, &max_version)) {
      return 0;
    }
  
    uint16_t session_version;
    if (max_version < TLS1_3_VERSION || ssl->session == NULL ||
        !ssl->method->version_from_wire(&session_version,
                                        ssl->session->ssl_version) ||
        session_version < TLS1_3_VERSION) {
      return 1;
    }
  
    CBB contents, identities, identity;
    if (!CBB_add_u16(out, TLSEXT_TYPE_pre_shared_key) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u16_length_prefixed(&contents, &identities) ||
        !CBB_add_u16_length_prefixed(&identities, &identity) ||
        !CBB_add_bytes(&identity, ssl->session->tlsext_tick,
                       ssl->session->tlsext_ticklen)) {
      return 0;
    }
  
    return CBB_flush(out);
  }
  
  int ssl_ext_pre_shared_key_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                               CBS *contents) {
    uint16_t psk_id;
    if (!CBS_get_u16(contents, &psk_id) ||
        CBS_len(contents) != 0) {
      *out_alert = SSL_AD_DECODE_ERROR;
      return 0;
    }
  
    if (psk_id != 0) {
      *out_alert = SSL_AD_UNKNOWN_PSK_IDENTITY;
      return 0;
    }
  
    return 1;
  }
  
  int ssl_ext_pre_shared_key_parse_clienthello(SSL *ssl,
                                               SSL_SESSION **out_session,
                                               uint8_t *out_alert,
                                               CBS *contents) {
    CBS identities, identity;
    if (!CBS_get_u16_length_prefixed(contents, &identities) ||
        !CBS_get_u16_length_prefixed(&identities, &identity) ||
        CBS_len(contents) != 0) {
      *out_alert = SSL_AD_DECODE_ERROR;
      return 0;
    }
  
    /* TLS 1.3 session tickets are renewed separately as part of the
     * NewSessionTicket. */
    int renew;
    return tls_process_ticket(ssl, out_session, &renew, CBS_data(&identity),
                              CBS_len(&identity), NULL, 0);
  }
  
  int ssl_ext_pre_shared_key_add_serverhello(SSL *ssl, CBB *out) {
    if (!ssl->s3->session_reused) {
      return 1;
    }
  
    CBB contents;
    if (!CBB_add_u16(out, TLSEXT_TYPE_pre_shared_key) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        /* We only consider the first identity for resumption */
        !CBB_add_u16(&contents, 0) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* Key Share
   *
   * https://tools.ietf.org/html/draft-ietf-tls-tls13-12 */
  
  static int ext_key_share_add_clienthello(SSL *ssl, CBB *out) {
    uint16_t min_version, max_version;
    if (!ssl_get_version_range(ssl, &min_version, &max_version)) {
      return 0;
    }
  
    if (max_version < TLS1_3_VERSION || !ssl_any_ec_cipher_suites_enabled(ssl)) {
      return 1;
    }
  
    CBB contents, kse_bytes;
    if (!CBB_add_u16(out, TLSEXT_TYPE_key_share) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u16_length_prefixed(&contents, &kse_bytes)) {
      return 0;
    }
  
    uint16_t group_id;
    if (ssl->s3->hs->retry_group) {
      /* Append the new key share to the old list. */
      if (!CBB_add_bytes(&kse_bytes, ssl->s3->hs->key_share_bytes,
                         ssl->s3->hs->key_share_bytes_len)) {
        return 0;
      }
      OPENSSL_free(ssl->s3->hs->key_share_bytes);
      ssl->s3->hs->key_share_bytes = NULL;
      ssl->s3->hs->key_share_bytes_len = 0;
  
      group_id = ssl->s3->hs->retry_group;
    } else {
      /* Add a fake group. See draft-davidben-tls-grease-01. */
      if (ssl->ctx->grease_enabled &&
          (!CBB_add_u16(&kse_bytes,
                        ssl_get_grease_value(ssl, ssl_grease_group)) ||
           !CBB_add_u16(&kse_bytes, 1 /* length */) ||
           !CBB_add_u8(&kse_bytes, 0 /* one byte key share */))) {
        return 0;
      }
  
      /* Predict the most preferred group. */
      const uint16_t *groups;
      size_t groups_len;
      tls1_get_grouplist(ssl, 0 /* local groups */, &groups, &groups_len);
      if (groups_len == 0) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_NO_GROUPS_SPECIFIED);
        return 0;
      }
  
      group_id = groups[0];
    }
  
    CBB key_exchange;
    if (!CBB_add_u16(&kse_bytes, group_id) ||
        !CBB_add_u16_length_prefixed(&kse_bytes, &key_exchange) ||
        !SSL_ECDH_CTX_init(&ssl->s3->hs->ecdh_ctx, group_id) ||
        !SSL_ECDH_CTX_offer(&ssl->s3->hs->ecdh_ctx, &key_exchange) ||
        !CBB_flush(&kse_bytes)) {
      return 0;
    }
  
    if (!ssl->s3->hs->retry_group) {
      /* Save the contents of the extension to repeat it in the second
       * ClientHello. */
      ssl->s3->hs->key_share_bytes_len = CBB_len(&kse_bytes);
      ssl->s3->hs->key_share_bytes = BUF_memdup(CBB_data(&kse_bytes),
                                                CBB_len(&kse_bytes));
      if (ssl->s3->hs->key_share_bytes == NULL) {
        return 0;
      }
    }
  
    return CBB_flush(out);
  }
  
  int ssl_ext_key_share_parse_serverhello(SSL *ssl, uint8_t **out_secret,
                                          size_t *out_secret_len,
                                          uint8_t *out_alert, CBS *contents) {
    CBS peer_key;
    uint16_t group_id;
    if (!CBS_get_u16(contents, &group_id) ||
        !CBS_get_u16_length_prefixed(contents, &peer_key) ||
        CBS_len(contents) != 0) {
      *out_alert = SSL_AD_DECODE_ERROR;
      return 0;
    }
  
    if (SSL_ECDH_CTX_get_id(&ssl->s3->hs->ecdh_ctx) != group_id) {
      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
      OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_CURVE);
      return 0;
    }
  
    if (!SSL_ECDH_CTX_finish(&ssl->s3->hs->ecdh_ctx, out_secret, out_secret_len,
                             out_alert, CBS_data(&peer_key),
                             CBS_len(&peer_key))) {
      *out_alert = SSL_AD_INTERNAL_ERROR;
      return 0;
    }
  
    ssl->s3->new_session->key_exchange_info = group_id;
    SSL_ECDH_CTX_cleanup(&ssl->s3->hs->ecdh_ctx);
    return 1;
  }
  
  int ssl_ext_key_share_parse_clienthello(SSL *ssl, int *out_found,
                                          uint8_t **out_secret,
                                          size_t *out_secret_len,
                                          uint8_t *out_alert, CBS *contents) {
    uint16_t group_id;
    CBS key_shares;
    if (!tls1_get_shared_group(ssl, &group_id) ||
        !CBS_get_u16_length_prefixed(contents, &key_shares) ||
        CBS_len(contents) != 0) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
      return 0;
    }
  
    /* Find the corresponding key share. */
    int found = 0;
    CBS peer_key;
    while (CBS_len(&key_shares) > 0) {
      uint16_t id;
      CBS peer_key_tmp;
      if (!CBS_get_u16(&key_shares, &id) ||
          !CBS_get_u16_length_prefixed(&key_shares, &peer_key_tmp)) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
        return 0;
      }
  
      if (id == group_id) {
        if (found) {
          OPENSSL_PUT_ERROR(SSL, SSL_R_DUPLICATE_KEY_SHARE);
          *out_alert = SSL_AD_ILLEGAL_PARAMETER;
          return 0;
        }
  
        found = 1;
        peer_key = peer_key_tmp;
        /* Continue parsing the structure to keep peers honest. */
      }
    }
  
    if (!found) {
      *out_found = 0;
      *out_secret = NULL;
      *out_secret_len = 0;
      return 1;
    }
  
    /* Compute the DH secret. */
    uint8_t *secret = NULL;
    size_t secret_len;
    SSL_ECDH_CTX group;
    memset(&group, 0, sizeof(SSL_ECDH_CTX));
    CBB public_key;
    if (!CBB_init(&public_key, 32) ||
        !SSL_ECDH_CTX_init(&group, group_id) ||
        !SSL_ECDH_CTX_accept(&group, &public_key, &secret, &secret_len,
                             out_alert, CBS_data(&peer_key),
                             CBS_len(&peer_key)) ||
        !CBB_finish(&public_key, &ssl->s3->hs->public_key,
                    &ssl->s3->hs->public_key_len)) {
      OPENSSL_free(secret);
      SSL_ECDH_CTX_cleanup(&group);
      CBB_cleanup(&public_key);
      return 0;
    }
  
    SSL_ECDH_CTX_cleanup(&group);
  
    *out_secret = secret;
    *out_secret_len = secret_len;
    *out_found = 1;
    return 1;
  }
  
  int ssl_ext_key_share_add_serverhello(SSL *ssl, CBB *out) {
    if (ssl->s3->tmp.new_cipher->algorithm_mkey != SSL_kECDHE) {
      return 1;
    }
  
    uint16_t group_id;
    CBB kse_bytes, public_key;
    if (!tls1_get_shared_group(ssl, &group_id) ||
        !CBB_add_u16(out, TLSEXT_TYPE_key_share) ||
        !CBB_add_u16_length_prefixed(out, &kse_bytes) ||
        !CBB_add_u16(&kse_bytes, group_id) ||
        !CBB_add_u16_length_prefixed(&kse_bytes, &public_key) ||
        !CBB_add_bytes(&public_key, ssl->s3->hs->public_key,
                       ssl->s3->hs->public_key_len) ||
        !CBB_flush(out)) {
      return 0;
    }
  
    OPENSSL_free(ssl->s3->hs->public_key);
    ssl->s3->hs->public_key = NULL;
    ssl->s3->hs->public_key_len = 0;
  
    ssl->s3->new_session->key_exchange_info = group_id;
    return 1;
  }
  
  
  /* Supported Versions
   *
   * https://tools.ietf.org/html/draft-ietf-tls-tls13-16#section-4.2.1 */
  
  static int ext_supported_versions_add_clienthello(SSL *ssl, CBB *out) {
    uint16_t min_version, max_version;
    if (!ssl_get_version_range(ssl, &min_version, &max_version)) {
      return 0;
    }
  
    if (max_version <= TLS1_2_VERSION) {
      return 1;
    }
  
    CBB contents, versions;
    if (!CBB_add_u16(out, TLSEXT_TYPE_supported_versions) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u8_length_prefixed(&contents, &versions)) {
      return 0;
    }
  
    /* Add a fake version. See draft-davidben-tls-grease-01. */
    if (ssl->ctx->grease_enabled &&
        !CBB_add_u16(&versions, ssl_get_grease_value(ssl, ssl_grease_version))) {
      return 0;
    }
  
    for (uint16_t version = max_version; version >= min_version; version--) {
      if (!CBB_add_u16(&versions, ssl->method->version_to_wire(version))) {
        return 0;
      }
    }
  
    if (!CBB_flush(out)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* Negotiated Groups
   *
   * https://tools.ietf.org/html/rfc4492#section-5.1.2
   * https://tools.ietf.org/html/draft-ietf-tls-tls13-12#section-6.3.2.2 */
  
  static void ext_supported_groups_init(SSL *ssl) {
    OPENSSL_free(ssl->s3->tmp.peer_supported_group_list);
    ssl->s3->tmp.peer_supported_group_list = NULL;
    ssl->s3->tmp.peer_supported_group_list_len = 0;
  }
  
  static int ext_supported_groups_add_clienthello(SSL *ssl, CBB *out) {
    if (!ssl_any_ec_cipher_suites_enabled(ssl)) {
      return 1;
    }
  
    CBB contents, groups_bytes;
    if (!CBB_add_u16(out, TLSEXT_TYPE_supported_groups) ||
        !CBB_add_u16_length_prefixed(out, &contents) ||
        !CBB_add_u16_length_prefixed(&contents, &groups_bytes)) {
      return 0;
    }
  
    /* Add a fake group. See draft-davidben-tls-grease-01. */
    if (ssl->ctx->grease_enabled &&
        !CBB_add_u16(&groups_bytes,
                     ssl_get_grease_value(ssl, ssl_grease_group))) {
      return 0;
    }
  
    const uint16_t *groups;
    size_t groups_len;
    tls1_get_grouplist(ssl, 0, &groups, &groups_len);
  
    for (size_t i = 0; i < groups_len; i++) {
      if (!CBB_add_u16(&groups_bytes, groups[i])) {
        return 0;
      }
    }
  
    return CBB_flush(out);
  }
  
  static int ext_supported_groups_parse_serverhello(SSL *ssl, uint8_t *out_alert,
                                                    CBS *contents) {
    /* This extension is not expected to be echoed by servers in TLS 1.2, but some
     * BigIP servers send it nonetheless, so do not enforce this. */
    return 1;
  }
  
  static int ext_supported_groups_parse_clienthello(SSL *ssl, uint8_t *out_alert,
                                                    CBS *contents) {
    if (contents == NULL) {
      return 1;
    }
  
    CBS supported_group_list;
    if (!CBS_get_u16_length_prefixed(contents, &supported_group_list) ||
        CBS_len(&supported_group_list) == 0 ||
        (CBS_len(&supported_group_list) & 1) != 0 ||
        CBS_len(contents) != 0) {
      return 0;
    }
  
    ssl->s3->tmp.peer_supported_group_list = OPENSSL_malloc(
        CBS_len(&supported_group_list));
    if (ssl->s3->tmp.peer_supported_group_list == NULL) {
      *out_alert = SSL_AD_INTERNAL_ERROR;
      return 0;
    }
  
    const size_t num_groups = CBS_len(&supported_group_list) / 2;
    for (size_t i = 0; i < num_groups; i++) {
      if (!CBS_get_u16(&supported_group_list,
                       &ssl->s3->tmp.peer_supported_group_list[i])) {
        goto err;
      }
    }
  
    assert(CBS_len(&supported_group_list) == 0);
    ssl->s3->tmp.peer_supported_group_list_len = num_groups;
  
    return 1;
  
  err:
    OPENSSL_free(ssl->s3->tmp.peer_supported_group_list);
    ssl->s3->tmp.peer_supported_group_list = NULL;
    *out_alert = SSL_AD_INTERNAL_ERROR;
    return 0;
  }
  
  static int ext_supported_groups_add_serverhello(SSL *ssl, CBB *out) {
    /* Servers don't echo this extension. */
    return 1;
  }
  
  
  /* kExtensions contains all the supported extensions. */
  static const struct tls_extension kExtensions[] = {
    {
      TLSEXT_TYPE_renegotiate,
      NULL,
      ext_ri_add_clienthello,
      ext_ri_parse_serverhello,
      ext_ri_parse_clienthello,
      ext_ri_add_serverhello,
    },
    {
      TLSEXT_TYPE_server_name,
      ext_sni_init,
      ext_sni_add_clienthello,
      ext_sni_parse_serverhello,
      ext_sni_parse_clienthello,
      ext_sni_add_serverhello,
    },
    {
      TLSEXT_TYPE_extended_master_secret,
      NULL,
      ext_ems_add_clienthello,
      ext_ems_parse_serverhello,
      ext_ems_parse_clienthello,
      ext_ems_add_serverhello,
    },
    {
      TLSEXT_TYPE_session_ticket,
      NULL,
      ext_ticket_add_clienthello,
      ext_ticket_parse_serverhello,
      /* Ticket extension client parsing is handled in ssl_session.c */
      ignore_parse_clienthello,
      ext_ticket_add_serverhello,
    },
    {
      TLSEXT_TYPE_signature_algorithms,
      NULL,
      ext_sigalgs_add_clienthello,
      forbid_parse_serverhello,
      ext_sigalgs_parse_clienthello,
      dont_add_serverhello,
    },
    {
      TLSEXT_TYPE_status_request,
      ext_ocsp_init,
      ext_ocsp_add_clienthello,
      ext_ocsp_parse_serverhello,
      ext_ocsp_parse_clienthello,
      ext_ocsp_add_serverhello,
    },
    {
      TLSEXT_TYPE_next_proto_neg,
      ext_npn_init,
      ext_npn_add_clienthello,
      ext_npn_parse_serverhello,
      ext_npn_parse_clienthello,
      ext_npn_add_serverhello,
    },
    {
      TLSEXT_TYPE_certificate_timestamp,
      NULL,
      ext_sct_add_clienthello,
      ext_sct_parse_serverhello,
      ext_sct_parse_clienthello,
      ext_sct_add_serverhello,
    },
    {
      TLSEXT_TYPE_application_layer_protocol_negotiation,
      ext_alpn_init,
      ext_alpn_add_clienthello,
      ext_alpn_parse_serverhello,
      ext_alpn_parse_clienthello,
      ext_alpn_add_serverhello,
    },
    {
      TLSEXT_TYPE_channel_id,
      ext_channel_id_init,
      ext_channel_id_add_clienthello,
      ext_channel_id_parse_serverhello,
      ext_channel_id_parse_clienthello,
      ext_channel_id_add_serverhello,
    },
    {
      TLSEXT_TYPE_srtp,
      ext_srtp_init,
      ext_srtp_add_clienthello,
      ext_srtp_parse_serverhello,
      ext_srtp_parse_clienthello,
      ext_srtp_add_serverhello,
    },
    {
      TLSEXT_TYPE_ec_point_formats,
      NULL,
      ext_ec_point_add_clienthello,
      ext_ec_point_parse_serverhello,
      ext_ec_point_parse_clienthello,
      ext_ec_point_add_serverhello,
    },
    {
      TLSEXT_TYPE_key_share,
      NULL,
      ext_key_share_add_clienthello,
      forbid_parse_serverhello,
      ignore_parse_clienthello,
      dont_add_serverhello,
    },
    {
      TLSEXT_TYPE_pre_shared_key,
      NULL,
      ext_pre_shared_key_add_clienthello,
      forbid_parse_serverhello,
      ignore_parse_clienthello,
      dont_add_serverhello,
    },
    {
      TLSEXT_TYPE_supported_versions,
      NULL,
      ext_supported_versions_add_clienthello,
      forbid_parse_serverhello,
      ignore_parse_clienthello,
      dont_add_serverhello,
    },
    /* The final extension must be non-empty. WebSphere Application Server 7.0 is
     * intolerant to the last extension being zero-length. See
     * https://crbug.com/363583. */
    {
      TLSEXT_TYPE_supported_groups,
      ext_supported_groups_init,
      ext_supported_groups_add_clienthello,
      ext_supported_groups_parse_serverhello,
      ext_supported_groups_parse_clienthello,
      ext_supported_groups_add_serverhello,
    },
  };
  
  #define kNumExtensions (sizeof(kExtensions) / sizeof(struct tls_extension))
  
  OPENSSL_COMPILE_ASSERT(kNumExtensions <=
                             sizeof(((SSL *)NULL)->s3->tmp.extensions.sent) * 8,
                         too_many_extensions_for_sent_bitset);
  OPENSSL_COMPILE_ASSERT(kNumExtensions <=
                             sizeof(((SSL *)NULL)->s3->tmp.extensions.received) *
                                 8,
                         too_many_extensions_for_received_bitset);
  
  static const struct tls_extension *tls_extension_find(uint32_t *out_index,
                                                        uint16_t value) {
    unsigned i;
    for (i = 0; i < kNumExtensions; i++) {
      if (kExtensions[i].value == value) {
        *out_index = i;
        return &kExtensions[i];
      }
    }
  
    return NULL;
  }
  
  int SSL_extension_supported(unsigned extension_value) {
    uint32_t index;
    return extension_value == TLSEXT_TYPE_padding ||
           tls_extension_find(&index, extension_value) != NULL;
  }
  
  int ssl_add_clienthello_tlsext(SSL *ssl, CBB *out, size_t header_len) {
    /* don't add extensions for SSLv3 unless doing secure renegotiation */
    if (ssl->client_version == SSL3_VERSION &&
        !ssl->s3->send_connection_binding) {
      return 1;
    }
  
    CBB extensions;
    if (!CBB_add_u16_length_prefixed(out, &extensions)) {
      goto err;
    }
  
    ssl->s3->tmp.extensions.sent = 0;
    ssl->s3->tmp.custom_extensions.sent = 0;
  
    for (size_t i = 0; i < kNumExtensions; i++) {
      if (kExtensions[i].init != NULL) {
        kExtensions[i].init(ssl);
      }
    }
  
    uint16_t grease_ext1 = 0;
    if (ssl->ctx->grease_enabled) {
      /* Add a fake empty extension. See draft-davidben-tls-grease-01. */
      grease_ext1 = ssl_get_grease_value(ssl, ssl_grease_extension1);
      if (!CBB_add_u16(&extensions, grease_ext1) ||
          !CBB_add_u16(&extensions, 0 /* zero length */)) {
        goto err;
      }
    }
  
    for (size_t i = 0; i < kNumExtensions; i++) {
      const size_t len_before = CBB_len(&extensions);
      if (!kExtensions[i].add_clienthello(ssl, &extensions)) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_ERROR_ADDING_EXTENSION);
        ERR_add_error_dataf("extension: %u", (unsigned)kExtensions[i].value);
        goto err;
      }
  
      if (CBB_len(&extensions) != len_before) {
        ssl->s3->tmp.extensions.sent |= (1u << i);
      }
    }
  
    if (!custom_ext_add_clienthello(ssl, &extensions)) {
      goto err;
    }
  
    if (ssl->ctx->grease_enabled) {
      /* Add a fake non-empty extension. See draft-davidben-tls-grease-01. */
      uint16_t grease_ext2 = ssl_get_grease_value(ssl, ssl_grease_extension2);
  
      /* The two fake extensions must not have the same value. GREASE values are
       * of the form 0x1a1a, 0x2a2a, 0x3a3a, etc., so XOR to generate a different
       * one. */
      if (grease_ext1 == grease_ext2) {
        grease_ext2 ^= 0x1010;
      }
  
      if (!CBB_add_u16(&extensions, grease_ext2) ||
          !CBB_add_u16(&extensions, 1 /* one byte length */) ||
          !CBB_add_u8(&extensions, 0 /* single zero byte as contents */)) {
        goto err;
      }
    }
  
    if (!SSL_is_dtls(ssl)) {
      header_len += 2 + CBB_len(&extensions);
      if (header_len > 0xff && header_len < 0x200) {
        /* Add padding to workaround bugs in F5 terminators. See RFC 7685.
         *
         * NB: because this code works out the length of all existing extensions
         * it MUST always appear last. */
        size_t padding_len = 0x200 - header_len;
        /* Extensions take at least four bytes to encode. Always include at least
         * one byte of data if including the extension. WebSphere Application
         * Server 7.0 is intolerant to the last extension being zero-length. See
         * https://crbug.com/363583. */
        if (padding_len >= 4 + 1) {
          padding_len -= 4;
        } else {
          padding_len = 1;
        }
  
        uint8_t *padding_bytes;
        if (!CBB_add_u16(&extensions, TLSEXT_TYPE_padding) ||
            !CBB_add_u16(&extensions, padding_len) ||
            !CBB_add_space(&extensions, &padding_bytes, padding_len)) {
          goto err;
        }
  
        memset(padding_bytes, 0, padding_len);
      }
    }
  
    /* Discard empty extensions blocks. */
    if (CBB_len(&extensions) == 0) {
      CBB_discard_child(out);
    }
  
    return CBB_flush(out);
  
  err:
    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    return 0;
  }
  
  int ssl_add_serverhello_tlsext(SSL *ssl, CBB *out) {
    CBB extensions;
    if (!CBB_add_u16_length_prefixed(out, &extensions)) {
      goto err;
    }
  
    unsigned i;
    for (i = 0; i < kNumExtensions; i++) {
      if (!(ssl->s3->tmp.extensions.received & (1u << i))) {
        /* Don't send extensions that were not received. */
        continue;
      }
  
      if (!kExtensions[i].add_serverhello(ssl, &extensions)) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_ERROR_ADDING_EXTENSION);
        ERR_add_error_dataf("extension: %u", (unsigned)kExtensions[i].value);
        goto err;
      }
    }
  
    if (!custom_ext_add_serverhello(ssl, &extensions)) {
      goto err;
    }
  
    /* Discard empty extensions blocks before TLS 1.3. */
    if (ssl3_protocol_version(ssl) < TLS1_3_VERSION &&
        CBB_len(&extensions) == 0) {
      CBB_discard_child(out);
    }
  
    return CBB_flush(out);
  
  err:
    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    return 0;
  }
  
  static int ssl_scan_clienthello_tlsext(
      SSL *ssl, const struct ssl_early_callback_ctx *client_hello,
      int *out_alert) {
    for (size_t i = 0; i < kNumExtensions; i++) {
      if (kExtensions[i].init != NULL) {
        kExtensions[i].init(ssl);
      }
    }
  
    ssl->s3->tmp.extensions.received = 0;
    ssl->s3->tmp.custom_extensions.received = 0;
  
    CBS extensions;
    CBS_init(&extensions, client_hello->extensions, client_hello->extensions_len);
    while (CBS_len(&extensions) != 0) {
      uint16_t type;
      CBS extension;
  
      /* Decode the next extension. */
      if (!CBS_get_u16(&extensions, &type) ||
          !CBS_get_u16_length_prefixed(&extensions, &extension)) {
        *out_alert = SSL_AD_DECODE_ERROR;
        return 0;
      }
  
      /* RFC 5746 made the existence of extensions in SSL 3.0 somewhat
       * ambiguous. Ignore all but the renegotiation_info extension. */
      if (ssl->version == SSL3_VERSION && type != TLSEXT_TYPE_renegotiate) {
        continue;
      }
  
      unsigned ext_index;
      const struct tls_extension *const ext =
          tls_extension_find(&ext_index, type);
  
      if (ext == NULL) {
        if (!custom_ext_parse_clienthello(ssl, out_alert, type, &extension)) {
          OPENSSL_PUT_ERROR(SSL, SSL_R_ERROR_PARSING_EXTENSION);
          return 0;
        }
        continue;
      }
  
      ssl->s3->tmp.extensions.received |= (1u << ext_index);
      uint8_t alert = SSL_AD_DECODE_ERROR;
      if (!ext->parse_clienthello(ssl, &alert, &extension)) {
        *out_alert = alert;
        OPENSSL_PUT_ERROR(SSL, SSL_R_ERROR_PARSING_EXTENSION);
        ERR_add_error_dataf("extension: %u", (unsigned)type);
        return 0;
      }
    }
  
    for (size_t i = 0; i < kNumExtensions; i++) {
      if (ssl->s3->tmp.extensions.received & (1u << i)) {
        continue;
      }
  
      CBS *contents = NULL, fake_contents;
      static const uint8_t kFakeRenegotiateExtension[] = {0};
      if (kExtensions[i].value == TLSEXT_TYPE_renegotiate &&
          ssl_client_cipher_list_contains_cipher(client_hello,
                                                 SSL3_CK_SCSV & 0xffff)) {
        /* The renegotiation SCSV was received so pretend that we received a
         * renegotiation extension. */
        CBS_init(&fake_contents, kFakeRenegotiateExtension,
                 sizeof(kFakeRenegotiateExtension));
        contents = &fake_contents;
        ssl->s3->tmp.extensions.received |= (1u << i);
      }
  
      /* Extension wasn't observed so call the callback with a NULL
       * parameter. */
      uint8_t alert = SSL_AD_DECODE_ERROR;
      if (!kExtensions[i].parse_clienthello(ssl, &alert, contents)) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_MISSING_EXTENSION);
        ERR_add_error_dataf("extension: %u", (unsigned)kExtensions[i].value);
        *out_alert = alert;
        return 0;
      }
    }
  
    return 1;
  }
  
  int ssl_parse_clienthello_tlsext(
      SSL *ssl, const struct ssl_early_callback_ctx *client_hello) {
    int alert = -1;
    if (ssl_scan_clienthello_tlsext(ssl, client_hello, &alert) <= 0) {
      ssl3_send_alert(ssl, SSL3_AL_FATAL, alert);
      return 0;
    }
  
    if (ssl_check_clienthello_tlsext(ssl) <= 0) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_CLIENTHELLO_TLSEXT);
      return 0;
    }
  
    return 1;
  }
  
  OPENSSL_COMPILE_ASSERT(kNumExtensions <= sizeof(uint32_t) * 8, too_many_bits);
  
  static int ssl_scan_serverhello_tlsext(SSL *ssl, CBS *cbs, int *out_alert) {
    /* Before TLS 1.3, ServerHello extensions blocks may be omitted if empty. */
    if (CBS_len(cbs) == 0 && ssl3_protocol_version(ssl) < TLS1_3_VERSION) {
      return 1;
    }
  
    /* Decode the extensions block and check it is valid. */
    CBS extensions;
    if (!CBS_get_u16_length_prefixed(cbs, &extensions) ||
        !tls1_check_duplicate_extensions(&extensions)) {
      *out_alert = SSL_AD_DECODE_ERROR;
      return 0;
    }
  
    uint32_t received = 0;
    while (CBS_len(&extensions) != 0) {
      uint16_t type;
      CBS extension;
  
      /* Decode the next extension. */
      if (!CBS_get_u16(&extensions, &type) ||
          !CBS_get_u16_length_prefixed(&extensions, &extension)) {
        *out_alert = SSL_AD_DECODE_ERROR;
        return 0;
      }
  
      unsigned ext_index;
      const struct tls_extension *const ext =
          tls_extension_find(&ext_index, type);
  
      if (ext == NULL) {
        if (!custom_ext_parse_serverhello(ssl, out_alert, type, &extension)) {
          return 0;
        }
        continue;
      }
  
      if (!(ssl->s3->tmp.extensions.sent & (1u << ext_index)) &&
          type != TLSEXT_TYPE_renegotiate) {
        /* If the extension was never sent then it is illegal, except for the
         * renegotiation extension which, in SSL 3.0, is signaled via SCSV. */
        OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_EXTENSION);
        ERR_add_error_dataf("extension :%u", (unsigned)type);
        *out_alert = SSL_AD_UNSUPPORTED_EXTENSION;
        return 0;
      }
  
      received |= (1u << ext_index);
  
      uint8_t alert = SSL_AD_DECODE_ERROR;
      if (!ext->parse_serverhello(ssl, &alert, &extension)) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_ERROR_PARSING_EXTENSION);
        ERR_add_error_dataf("extension: %u", (unsigned)type);
        *out_alert = alert;
        return 0;
      }
    }
  
    for (size_t i = 0; i < kNumExtensions; i++) {
      if (!(received & (1u << i))) {
        /* Extension wasn't observed so call the callback with a NULL
         * parameter. */
        uint8_t alert = SSL_AD_DECODE_ERROR;
        if (!kExtensions[i].parse_serverhello(ssl, &alert, NULL)) {
          OPENSSL_PUT_ERROR(SSL, SSL_R_MISSING_EXTENSION);
          ERR_add_error_dataf("extension: %u", (unsigned)kExtensions[i].value);
          *out_alert = alert;
          return 0;
        }
      }
    }
  
    return 1;
  }
  
  static int ssl_check_clienthello_tlsext(SSL *ssl) {
    int ret = SSL_TLSEXT_ERR_NOACK;
    int al = SSL_AD_UNRECOGNIZED_NAME;
  
    if (ssl->ctx->tlsext_servername_callback != 0) {
      ret = ssl->ctx->tlsext_servername_callback(ssl, &al,
                                                 ssl->ctx->tlsext_servername_arg);
    } else if (ssl->initial_ctx->tlsext_servername_callback != 0) {
      ret = ssl->initial_ctx->tlsext_servername_callback(
          ssl, &al, ssl->initial_ctx->tlsext_servername_arg);
    }
  
    switch (ret) {
      case SSL_TLSEXT_ERR_ALERT_FATAL:
        ssl3_send_alert(ssl, SSL3_AL_FATAL, al);
        return -1;
  
      case SSL_TLSEXT_ERR_ALERT_WARNING:
        ssl3_send_alert(ssl, SSL3_AL_WARNING, al);
        return 1;
  
      case SSL_TLSEXT_ERR_NOACK:
        ssl->s3->tmp.should_ack_sni = 0;
        return 1;
  
      default:
        return 1;
    }
  }
  
  static int ssl_check_serverhello_tlsext(SSL *ssl) {
    int ret = SSL_TLSEXT_ERR_OK;
    int al = SSL_AD_UNRECOGNIZED_NAME;
  
    if (ssl->ctx->tlsext_servername_callback != 0) {
      ret = ssl->ctx->tlsext_servername_callback(ssl, &al,
                                                 ssl->ctx->tlsext_servername_arg);
    } else if (ssl->initial_ctx->tlsext_servername_callback != 0) {
      ret = ssl->initial_ctx->tlsext_servername_callback(
          ssl, &al, ssl->initial_ctx->tlsext_servername_arg);
    }
  
    switch (ret) {
      case SSL_TLSEXT_ERR_ALERT_FATAL:
        ssl3_send_alert(ssl, SSL3_AL_FATAL, al);
        return -1;
  
      case SSL_TLSEXT_ERR_ALERT_WARNING:
        ssl3_send_alert(ssl, SSL3_AL_WARNING, al);
        return 1;
  
      default:
        return 1;
    }
  }
  
  int ssl_parse_serverhello_tlsext(SSL *ssl, CBS *cbs) {
    int alert = -1;
    if (ssl_scan_serverhello_tlsext(ssl, cbs, &alert) <= 0) {
      ssl3_send_alert(ssl, SSL3_AL_FATAL, alert);
      return 0;
    }
  
    if (ssl_check_serverhello_tlsext(ssl) <= 0) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_SERVERHELLO_TLSEXT);
      return 0;
    }
  
    return 1;
  }
  
  int tls_process_ticket(SSL *ssl, SSL_SESSION **out_session,
                         int *out_renew_ticket, const uint8_t *ticket,
                         size_t ticket_len, const uint8_t *session_id,
                         size_t session_id_len) {
    int ret = 1; /* Most errors are non-fatal. */
    SSL_CTX *ssl_ctx = ssl->initial_ctx;
    uint8_t *plaintext = NULL;
  
    HMAC_CTX hmac_ctx;
    HMAC_CTX_init(&hmac_ctx);
    EVP_CIPHER_CTX cipher_ctx;
    EVP_CIPHER_CTX_init(&cipher_ctx);
  
    *out_renew_ticket = 0;
    *out_session = NULL;
  
    if (SSL_get_options(ssl) & SSL_OP_NO_TICKET) {
      goto done;
    }
  
    if (session_id_len > SSL_MAX_SSL_SESSION_ID_LENGTH) {
      goto done;
    }
  
    /* Ensure there is room for the key name and the largest IV
     * |tlsext_ticket_key_cb| may try to consume. The real limit may be lower, but
     * the maximum IV length should be well under the minimum size for the
     * session material and HMAC. */
    if (ticket_len < SSL_TICKET_KEY_NAME_LEN + EVP_MAX_IV_LENGTH) {
      goto done;
    }
    const uint8_t *iv = ticket + SSL_TICKET_KEY_NAME_LEN;
  
    if (ssl_ctx->tlsext_ticket_key_cb != NULL) {
      int cb_ret = ssl_ctx->tlsext_ticket_key_cb(
          ssl, (uint8_t *)ticket /* name */, (uint8_t *)iv, &cipher_ctx,
          &hmac_ctx, 0 /* decrypt */);
      if (cb_ret < 0) {
        ret = 0;
        goto done;
      }
      if (cb_ret == 0) {
        goto done;
      }
      if (cb_ret == 2) {
        *out_renew_ticket = 1;
      }
    } else {
      /* Check the key name matches. */
      if (memcmp(ticket, ssl_ctx->tlsext_tick_key_name,
                 SSL_TICKET_KEY_NAME_LEN) != 0) {
        goto done;
      }
      if (!HMAC_Init_ex(&hmac_ctx, ssl_ctx->tlsext_tick_hmac_key,
                        sizeof(ssl_ctx->tlsext_tick_hmac_key), tlsext_tick_md(),
                        NULL) ||
          !EVP_DecryptInit_ex(&cipher_ctx, EVP_aes_128_cbc(), NULL,
                              ssl_ctx->tlsext_tick_aes_key, iv)) {
        ret = 0;
        goto done;
      }
    }
    size_t iv_len = EVP_CIPHER_CTX_iv_length(&cipher_ctx);
  
    /* Check the MAC at the end of the ticket. */
    uint8_t mac[EVP_MAX_MD_SIZE];
    size_t mac_len = HMAC_size(&hmac_ctx);
    if (ticket_len < SSL_TICKET_KEY_NAME_LEN + iv_len + 1 + mac_len) {
      /* The ticket must be large enough for key name, IV, data, and MAC. */
      goto done;
    }
    HMAC_Update(&hmac_ctx, ticket, ticket_len - mac_len);
    HMAC_Final(&hmac_ctx, mac, NULL);
    int mac_ok =
        CRYPTO_memcmp(mac, ticket + (ticket_len - mac_len), mac_len) == 0;
  #if defined(BORINGSSL_UNSAFE_FUZZER_MODE)
    mac_ok = 1;
  #endif
    if (!mac_ok) {
      goto done;
    }
  
    /* Decrypt the session data. */
    const uint8_t *ciphertext = ticket + SSL_TICKET_KEY_NAME_LEN + iv_len;
    size_t ciphertext_len = ticket_len - SSL_TICKET_KEY_NAME_LEN - iv_len -
                            mac_len;
    plaintext = OPENSSL_malloc(ciphertext_len);
    if (plaintext == NULL) {
      ret = 0;
      goto done;
    }
    size_t plaintext_len;
  #if defined(BORINGSSL_UNSAFE_FUZZER_MODE)
    memcpy(plaintext, ciphertext, ciphertext_len);
    plaintext_len = ciphertext_len;
  #else
    if (ciphertext_len >= INT_MAX) {
      goto done;
    }
    int len1, len2;
    if (!EVP_DecryptUpdate(&cipher_ctx, plaintext, &len1, ciphertext,
                           (int)ciphertext_len) ||
        !EVP_DecryptFinal_ex(&cipher_ctx, plaintext + len1, &len2)) {
      ERR_clear_error(); /* Don't leave an error on the queue. */
      goto done;
    }
    plaintext_len = (size_t)(len1 + len2);
  #endif
  
    /* Decode the session. */
    SSL_SESSION *session = SSL_SESSION_from_bytes(plaintext, plaintext_len);
    if (session == NULL) {
      ERR_clear_error(); /* Don't leave an error on the queue. */
      goto done;
    }
  
    /* Copy the client's session ID into the new session, to denote the ticket has
     * been accepted. */
    memcpy(session->session_id, session_id, session_id_len);
    session->session_id_length = session_id_len;
  
    if (!ssl_session_is_context_valid(ssl, session) ||
        !ssl_session_is_time_valid(ssl, session)) {
      SSL_SESSION_free(session);
      session = NULL;
    }
  
    *out_session = session;
  
  done:
    OPENSSL_free(plaintext);
    HMAC_CTX_cleanup(&hmac_ctx);
    EVP_CIPHER_CTX_cleanup(&cipher_ctx);
    return ret;
  }
  
  int tls1_parse_peer_sigalgs(SSL *ssl, const CBS *in_sigalgs) {
    /* Extension ignored for inappropriate versions */
    if (ssl3_protocol_version(ssl) < TLS1_2_VERSION) {
      return 1;
    }
  
    SSL_HANDSHAKE *hs = ssl->s3->hs;
    OPENSSL_free(hs->peer_sigalgs);
    hs->peer_sigalgs = NULL;
    hs->num_peer_sigalgs = 0;
  
    size_t num_sigalgs = CBS_len(in_sigalgs);
    if (num_sigalgs % 2 != 0) {
      return 0;
    }
    num_sigalgs /= 2;
  
    /* supported_signature_algorithms in the certificate request is
     * allowed to be empty. */
    if (num_sigalgs == 0) {
      return 1;
    }
  
    /* This multiplication doesn't overflow because sizeof(uint16_t) is two
     * and we just divided |num_sigalgs| by two. */
    hs->peer_sigalgs = OPENSSL_malloc(num_sigalgs * sizeof(uint16_t));
    if (hs->peer_sigalgs == NULL) {
      return 0;
    }
    hs->num_peer_sigalgs = num_sigalgs;
  
    CBS sigalgs;
    CBS_init(&sigalgs, CBS_data(in_sigalgs), CBS_len(in_sigalgs));
    for (size_t i = 0; i < num_sigalgs; i++) {
      if (!CBS_get_u16(&sigalgs, &hs->peer_sigalgs[i])) {
        return 0;
      }
    }
  
    return 1;
  }
  
  int tls1_choose_signature_algorithm(SSL *ssl, uint16_t *out) {
    CERT *cert = ssl->cert;
    SSL_HANDSHAKE *hs = ssl->s3->hs;
  
    /* Before TLS 1.2, the signature algorithm isn't negotiated as part of the
     * handshake. It is fixed at MD5-SHA1 for RSA and SHA1 for ECDSA. */
    if (ssl3_protocol_version(ssl) < TLS1_2_VERSION) {
      int type = ssl_private_key_type(ssl);
      if (type == NID_rsaEncryption) {
        *out = SSL_SIGN_RSA_PKCS1_MD5_SHA1;
        return 1;
      }
      if (ssl_is_ecdsa_key_type(type)) {
        *out = SSL_SIGN_ECDSA_SHA1;
        return 1;
      }
      OPENSSL_PUT_ERROR(SSL, SSL_R_NO_COMMON_SIGNATURE_ALGORITHMS);
      return 0;
    }
  
    const uint16_t *sigalgs;
    size_t num_sigalgs = tls12_get_psigalgs(ssl, &sigalgs);
    if (cert->sigalgs != NULL) {
      sigalgs = cert->sigalgs;
      num_sigalgs = cert->num_sigalgs;
    }
  
    const uint16_t *peer_sigalgs = hs->peer_sigalgs;
    size_t num_peer_sigalgs = hs->num_peer_sigalgs;
    if (num_peer_sigalgs == 0 && ssl3_protocol_version(ssl) < TLS1_3_VERSION) {
      /* If the client didn't specify any signature_algorithms extension then
       * we can assume that it supports SHA1. See
       * http://tools.ietf.org/html/rfc5246#section-7.4.1.4.1 */
      static const uint16_t kDefaultPeerAlgorithms[] = {SSL_SIGN_RSA_PKCS1_SHA1,
                                                        SSL_SIGN_ECDSA_SHA1};
      peer_sigalgs = kDefaultPeerAlgorithms;
      num_peer_sigalgs = OPENSSL_ARRAY_SIZE(kDefaultPeerAlgorithms);
    }
  
    for (size_t i = 0; i < num_sigalgs; i++) {
      uint16_t sigalg = sigalgs[i];
      /* SSL_SIGN_RSA_PKCS1_MD5_SHA1 is an internal value and should never be
       * negotiated. */
      if (sigalg == SSL_SIGN_RSA_PKCS1_MD5_SHA1 ||
          !ssl_private_key_supports_signature_algorithm(ssl, sigalgs[i])) {
        continue;
      }
  
      for (size_t j = 0; j < num_peer_sigalgs; j++) {
        if (sigalg == peer_sigalgs[j]) {
          *out = sigalg;
          return 1;
        }
      }
    }
  
    OPENSSL_PUT_ERROR(SSL, SSL_R_NO_COMMON_SIGNATURE_ALGORITHMS);
    return 0;
  }
  
  int tls1_channel_id_hash(SSL *ssl, uint8_t *out, size_t *out_len) {
    int ret = 0;
    EVP_MD_CTX ctx;
  
    EVP_MD_CTX_init(&ctx);
    if (!EVP_DigestInit_ex(&ctx, EVP_sha256(), NULL)) {
      goto err;
    }
  
    static const char kClientIDMagic[] = "TLS Channel ID signature";
    EVP_DigestUpdate(&ctx, kClientIDMagic, sizeof(kClientIDMagic));
  
    if (ssl->session != NULL) {
      static const char kResumptionMagic[] = "Resumption";
      EVP_DigestUpdate(&ctx, kResumptionMagic, sizeof(kResumptionMagic));
      if (ssl->session->original_handshake_hash_len == 0) {
        OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
        goto err;
      }
      EVP_DigestUpdate(&ctx, ssl->session->original_handshake_hash,
                       ssl->session->original_handshake_hash_len);
    }
  
    uint8_t handshake_hash[EVP_MAX_MD_SIZE];
    int handshake_hash_len = tls1_handshake_digest(ssl, handshake_hash,
                                                   sizeof(handshake_hash));
    if (handshake_hash_len < 0) {
      goto err;
    }
    EVP_DigestUpdate(&ctx, handshake_hash, (size_t)handshake_hash_len);
    unsigned len_u;
    EVP_DigestFinal_ex(&ctx, out, &len_u);
    *out_len = len_u;
  
    ret = 1;
  
  err:
    EVP_MD_CTX_cleanup(&ctx);
    return ret;
  }
  
  /* tls1_record_handshake_hashes_for_channel_id records the current handshake
   * hashes in |ssl->s3->new_session| so that Channel ID resumptions can sign that
   * data. */
  int tls1_record_handshake_hashes_for_channel_id(SSL *ssl) {
    int digest_len;
    /* This function should never be called for a resumed session because the
     * handshake hashes that we wish to record are for the original, full
     * handshake. */
    if (ssl->session != NULL) {
      return -1;
    }
  
    digest_len =
        tls1_handshake_digest(
            ssl, ssl->s3->new_session->original_handshake_hash,
            sizeof(ssl->s3->new_session->original_handshake_hash));
    if (digest_len < 0) {
      return -1;
    }
  
    ssl->s3->new_session->original_handshake_hash_len = digest_len;
  
    return 1;
  }
  