/src/gnutls/lib/auth/cert.c

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/*
 * Copyright (C) 2001-2012 Free Software Foundation, Inc.
 * Copyright (C) 2017 Red Hat, Inc.
 *
 * Author: Nikos Mavrogiannopoulos
 *
 * This file is part of GnuTLS.
 *
 * The GnuTLS is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>
 *
 */

/* The certificate authentication functions which are needed in the handshake,
 * and are common to RSA and DHE key exchange, are in this file.
 */

#include "gnutls_int.h"
#include "auth.h"
#include "errors.h"
#include <auth/cert.h>
#include "dh.h"
#include "num.h"
#include "libtasn1.h"
#include "datum.h"
#include "ext/signature.h"
#include <pk.h>
#include <algorithms.h>
#include <global.h>
#include <record.h>
#include <tls-sig.h>
#include <state.h>
#include <pk.h>
#include <x509.h>
#include <x509/verify-high.h>
#include <gnutls/abstract.h>
#include "abstract_int.h"
#include "debug.h"

static void
selected_certs_set(gnutls_session_t session,
       gnutls_pcert_st * certs, int ncerts,
       gnutls_ocsp_data_st * ocsp, unsigned nocsp,
       gnutls_privkey_t key, int need_free,
       gnutls_status_request_ocsp_func ocsp_func,
       void *ocsp_func_ptr);

#define MAX_CLIENT_SIGN_ALGOS 5
#define CERTTYPE_SIZE (MAX_CLIENT_SIGN_ALGOS+1)
typedef enum CertificateSigType { RSA_SIGN = 1, DSA_SIGN = 2, ECDSA_SIGN = 64,
#ifdef ENABLE_GOST
  GOSTR34102012_256_SIGN = 67,
  GOSTR34102012_512_SIGN = 68
#endif
} CertificateSigType;

enum CertificateSigTypeFlags {
  RSA_SIGN_FLAG = 1,
  DSA_SIGN_FLAG = 1 << 1,
  ECDSA_SIGN_FLAG = 1 << 2,
#ifdef ENABLE_GOST
  GOSTR34102012_256_SIGN_FLAG = 1 << 3,
  GOSTR34102012_512_SIGN_FLAG = 1 << 4
#endif
};

/* Moves data from an internal certificate struct (gnutls_pcert_st) to
 * another internal certificate struct (cert_auth_info_t), and deinitializes
 * the former.
 */
int _gnutls_pcert_to_auth_info(cert_auth_info_t info, gnutls_pcert_st * certs,
             size_t ncerts)
{
  size_t i, j;

  if (info->raw_certificate_list != NULL) {
    for (j = 0; j < info->ncerts; j++)
      _gnutls_free_datum(&info->raw_certificate_list[j]);
    gnutls_free(info->raw_certificate_list);
  }

  if (ncerts == 0) {
    info->raw_certificate_list = NULL;
    info->ncerts = 0;
    return 0;
  }

  info->raw_certificate_list =
      gnutls_calloc(ncerts, sizeof(gnutls_datum_t));
  if (info->raw_certificate_list == NULL) {
    gnutls_assert();
    return GNUTLS_E_MEMORY_ERROR;
  }

  info->cert_type = certs[0].type;
  info->ncerts = ncerts;

  for (i = 0; i < ncerts; i++) {
    info->raw_certificate_list[i].data = certs[i].cert.data;
    info->raw_certificate_list[i].size = certs[i].cert.size;
    certs[i].cert.data = NULL;
    gnutls_pcert_deinit(&certs[i]);
  }
  gnutls_free(certs);

  return 0;
}

/* returns 0 if the algo_to-check exists in the pk_algos list,
 * -1 otherwise.
 */
inline static int
check_pk_algo_in_list(const gnutls_pk_algorithm_t *
          pk_algos, int pk_algos_length,
          gnutls_pk_algorithm_t algo_to_check)
{
  int i;
  for (i = 0; i < pk_algos_length; i++) {
    if (algo_to_check == pk_algos[i]) {
      return 0;
    }
  }
  return -1;
}

/* Returns the issuer's Distinguished name in odn, of the certificate
 * specified in cert.
 */
static int cert_get_issuer_dn(gnutls_pcert_st * cert, gnutls_datum_t * odn)
{
  asn1_node dn;
  int len, result;
  int start, end;

  if ((result = asn1_create_element
       (_gnutls_get_pkix(), "PKIX1.Certificate", &dn)) != ASN1_SUCCESS) {
    gnutls_assert();
    return _gnutls_asn2err(result);
  }

  result = asn1_der_decoding(&dn, cert->cert.data, cert->cert.size, NULL);
  if (result != ASN1_SUCCESS) {
    /* couldn't decode DER */
    gnutls_assert();
    asn1_delete_structure(&dn);
    return _gnutls_asn2err(result);
  }

  result =
      asn1_der_decoding_startEnd(dn, cert->cert.data,
               cert->cert.size,
               "tbsCertificate.issuer", &start, &end);

  if (result != ASN1_SUCCESS) {
    /* couldn't decode DER */
    gnutls_assert();
    asn1_delete_structure(&dn);
    return _gnutls_asn2err(result);
  }
  asn1_delete_structure(&dn);

  len = end - start + 1;

  odn->size = len;
  odn->data = &cert->cert.data[start];

  return 0;
}

/* Locates the most appropriate x509 certificate using the
 * given DN. If indx == -1 then no certificate was found.
 *
 * That is to guess which certificate to use, based on the
 * CAs and sign algorithms supported by the peer server.
 */
static int
find_x509_client_cert(gnutls_session_t session,
          const gnutls_certificate_credentials_t cred,
          const uint8_t * _data, size_t _data_size,
          const gnutls_pk_algorithm_t * pk_algos,
          int pk_algos_length, int *indx)
{
  unsigned size;
  gnutls_datum_t odn = { NULL, 0 }, asked_dn;
  const uint8_t *data = _data;
  ssize_t data_size = _data_size;
  unsigned i, j;
  int result, cert_pk;
  unsigned key_usage;

  *indx = -1;

  /* If peer doesn't send any issuers and we have a single certificate
   * then send that one.
   */
  if (cred->ncerts == 1 &&
      (data_size == 0
       || (session->internals.flags & GNUTLS_FORCE_CLIENT_CERT))) {
    if (cred->certs[0].cert_list[0].type == GNUTLS_CRT_X509) {

      key_usage =
          get_key_usage(session,
            cred->certs[0].cert_list[0].pubkey);

      /* For client certificates we require signatures */
      result =
          _gnutls_check_key_usage_for_sig(session, key_usage,
                  1);
      if (result < 0) {
        _gnutls_debug_log
            ("Client certificate is not suitable for signing\n");
        return gnutls_assert_val(result);
      }

      *indx = 0;
      return 0;
    }
  }

  do {
    DECR_LENGTH_RET(data_size, 2, 0);
    size = _gnutls_read_uint16(data);
    DECR_LENGTH_RET(data_size, size, 0);
    data += 2;

    asked_dn.data = (void *)data;
    asked_dn.size = size;
    _gnutls_dn_log("Peer requested CA", &asked_dn);

    for (i = 0; i < cred->ncerts; i++) {
      for (j = 0; j < cred->certs[i].cert_list_length; j++) {
        if ((result =
             cert_get_issuer_dn(&cred->certs
              [i].cert_list
              [j], &odn)) < 0) {
          gnutls_assert();
          return result;
        }

        if (odn.size == 0 || odn.size != asked_dn.size)
          continue;

        key_usage =
            get_key_usage(session,
              cred->certs[i].
              cert_list[0].pubkey);

        /* For client certificates we require signatures */
        if (_gnutls_check_key_usage_for_sig
            (session, key_usage, 1) < 0) {
          _gnutls_debug_log
              ("Client certificate is not suitable for signing\n");
          continue;
        }

        /* If the DN matches and
         * the *_SIGN algorithm matches
         * the cert is our cert!
         */
        cert_pk =
            gnutls_pubkey_get_pk_algorithm(cred->certs
                   [i].cert_list
                   [0].pubkey,
                   NULL);

        if ((memcmp
             (odn.data, asked_dn.data,
              asked_dn.size) == 0)
            &&
            (check_pk_algo_in_list
             (pk_algos, pk_algos_length,
              cert_pk) == 0)) {
          *indx = i;
          break;
        }
      }
      if (*indx != -1)
        break;
    }

    if (*indx != -1)
      break;

    /* move to next record */
    data += size;
  }
  while (1);

  return 0;

}

/* Locates the first raw public-key.
 * Currently it only makes sense to associate one raw pubkey per session.
 * Associating more raw pubkeys with a session has no use because we
 * don't know how to select the correct one.
 */
static int
find_rawpk_client_cert(gnutls_session_t session,
           const gnutls_certificate_credentials_t cred,
           const gnutls_pk_algorithm_t * pk_algos,
           int pk_algos_length, int *indx)
{
  unsigned i;
  int ret;
  gnutls_pk_algorithm_t pk;

  *indx = -1;

  for (i = 0; i < cred->ncerts; i++) {
    /* We know that our list length will be 1, therefore we can
     * ignore the rest.
     */
    if (cred->certs[i].cert_list_length == 1
        && cred->certs[i].cert_list[0].type == GNUTLS_CRT_RAWPK) {
      pk = gnutls_pubkey_get_pk_algorithm(cred->
                  certs[i].cert_list
                  [0].pubkey, NULL);

      /* For client certificates we require signatures */
      ret =
          _gnutls_check_key_usage_for_sig(session,
                  get_key_usage
                  (session,
                   cred->
                   certs[i].cert_list
                   [0].pubkey), 1);
      if (ret < 0) {
        /* we return an error instead of skipping so that the user is notified about
         * the key incompatibility */
        _gnutls_debug_log
            ("Client certificate is not suitable for signing\n");
        return gnutls_assert_val(ret);
      }

      /* Check whether the public-key algorithm of our credential is in
       * the list with supported public-key algorithms and whether the
       * cert type matches. */
      if ((check_pk_algo_in_list
           (pk_algos, pk_algos_length, pk) == 0)) {
        // We found a compatible credential
        *indx = i;
        break;
      }
    }
  }

  return 0;
}

/* Returns the number of issuers in the server's
 * certificate request packet.
 */
static int
get_issuers_num(gnutls_session_t session, const uint8_t * data,
    ssize_t data_size)
{
  int issuers_dn_len = 0;
  unsigned size;

  /* Count the number of the given issuers;
   * This is used to allocate the issuers_dn without
   * using realloc().
   */

  if (data_size == 0 || data == NULL)
    return 0;

  while (data_size > 0) {
    /* This works like DECR_LEN()
     */
    DECR_LENGTH_RET(data_size, 2,
        GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
    size = _gnutls_read_uint16(data);

    DECR_LENGTH_RET(data_size, size,
        GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

    data += 2;

    if (size > 0) {
      issuers_dn_len++;
      data += size;
    }
  }

  return issuers_dn_len;
}

/* Returns the issuers in the server's certificate request
 * packet.
 */
static int
get_issuers(gnutls_session_t session,
      gnutls_datum_t * issuers_dn, int issuers_len,
      const uint8_t * data, size_t data_size)
{
  int i;
  unsigned size;

  if (get_certificate_type(session, GNUTLS_CTYPE_CLIENT) !=
      GNUTLS_CRT_X509)
    return 0;

  /* put the requested DNs to req_dn, only in case
   * of X509 certificates.
   */
  if (issuers_len > 0) {

    for (i = 0; i < issuers_len; i++) {
      /* The checks here for the buffer boundaries
       * are not needed since the buffer has been
       * parsed above.
       */
      data_size -= 2;

      size = _gnutls_read_uint16(data);

      data += 2;

      issuers_dn[i].data = (void *)data;
      issuers_dn[i].size = size;

      _gnutls_dn_log("Peer requested CA", &issuers_dn[i]);

      data += size;
    }
  }

  return 0;
}

/* Calls the client or server certificate get callback.
 */
static int
call_get_cert_callback(gnutls_session_t session,
           const gnutls_datum_t * issuers_dn,
           int issuers_dn_length,
           gnutls_pk_algorithm_t * pk_algos, int pk_algos_length)
{
  gnutls_privkey_t local_key = NULL;
  int ret = GNUTLS_E_INTERNAL_ERROR;
  gnutls_certificate_type_t type;
  gnutls_certificate_credentials_t cred;
  gnutls_pcert_st *pcert = NULL;
  gnutls_ocsp_data_st *ocsp = NULL;
  unsigned int ocsp_length = 0;
  unsigned int pcert_length = 0;

  cred = (gnutls_certificate_credentials_t)
      _gnutls_get_cred(session, GNUTLS_CRD_CERTIFICATE);
  if (cred == NULL) {
    gnutls_assert();
    return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
  }

  /* Correctly set the certificate type for ourselves */
  type = get_certificate_type(session, GNUTLS_CTYPE_OURS);

  /* Check whether a callback is set and call it */
  if (cred->get_cert_callback3) {
    struct gnutls_cert_retr_st info;
    unsigned int flags = 0;

    memset(&info, 0, sizeof(info));
    info.req_ca_rdn = issuers_dn;
    info.nreqs = issuers_dn_length;
    info.pk_algos = pk_algos;
    info.pk_algos_length = pk_algos_length;
    info.cred = cred;

    /* we avoid all allocations and transformations */
    ret =
        cred->get_cert_callback3(session, &info,
               &pcert, &pcert_length,
               &ocsp, &ocsp_length,
               &local_key, &flags);
    if (ret < 0)
      return gnutls_assert_val(GNUTLS_E_USER_ERROR);

    if (pcert_length > 0 && type != pcert[0].type)
      return gnutls_assert_val(GNUTLS_E_INVALID_REQUEST);

    if (pcert_length == 0) {
      pcert = NULL;
      local_key = NULL;
    }

    selected_certs_set(session, pcert, pcert_length,
           ocsp, ocsp_length,
           local_key,
           (flags & GNUTLS_CERT_RETR_DEINIT_ALL) ? 1 :
           0, cred->glob_ocsp_func,
           cred->glob_ocsp_func_ptr);

    return 0;
  } else {
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
  }
}

/* Finds the appropriate certificate depending on the cA Distinguished name
 * advertized by the server. If none matches then returns 0 and -1 as index.
 * In case of an error a negative error code, is returned.
 *
 * 20020128: added ability to select a certificate depending on the SIGN
 * algorithm (only in automatic mode).
 */
int
_gnutls_select_client_cert(gnutls_session_t session,
         const uint8_t * _data, size_t _data_size,
         gnutls_pk_algorithm_t * pk_algos,
         int pk_algos_length)
{
  int result;
  int indx = -1;
  gnutls_certificate_credentials_t cred;
  const uint8_t *data = _data;
  ssize_t data_size = _data_size;
  int issuers_dn_length;
  gnutls_datum_t *issuers_dn = NULL;
  gnutls_certificate_type_t cert_type;

  cred = (gnutls_certificate_credentials_t)
      _gnutls_get_cred(session, GNUTLS_CRD_CERTIFICATE);
  if (cred == NULL) {
    gnutls_assert();
    return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
  }

  cert_type = get_certificate_type(session, GNUTLS_CTYPE_CLIENT);

  if (cred->get_cert_callback3 != NULL) {

    /* use a callback to get certificate
     */
    if (cert_type == GNUTLS_CRT_X509) {
      issuers_dn_length =
          get_issuers_num(session, data, data_size);
      if (issuers_dn_length < 0) {
        gnutls_assert();
        return issuers_dn_length;
      }

      if (issuers_dn_length > 0) {
        issuers_dn =
            gnutls_malloc(sizeof(gnutls_datum_t) *
              issuers_dn_length);
        if (issuers_dn == NULL) {
          gnutls_assert();
          return GNUTLS_E_MEMORY_ERROR;
        }

        result =
            get_issuers(session, issuers_dn,
            issuers_dn_length, data,
            data_size);
        if (result < 0) {
          gnutls_assert();
          goto cleanup;
        }
      }
    } else {
      issuers_dn_length = 0;
    }

    result =
        call_get_cert_callback(session, issuers_dn,
             issuers_dn_length, pk_algos,
             pk_algos_length);
    goto cleanup;

  } else {
    /* If we have no callbacks, try to guess.
     */
    switch (cert_type) {
    case GNUTLS_CRT_X509:
      result = find_x509_client_cert(session, cred, _data,
                   _data_size, pk_algos,
                   pk_algos_length, &indx);
      break;
    case GNUTLS_CRT_RAWPK:
      result = find_rawpk_client_cert(session, cred,
              pk_algos,
              pk_algos_length, &indx);
      break;
    default:
      result = GNUTLS_E_UNSUPPORTED_CERTIFICATE_TYPE;
      break;
    }

    if (result < 0) {
      return gnutls_assert_val(result);
    }

    if (indx >= 0) {
      selected_certs_set(session,
             &cred->certs[indx].cert_list[0],
             cred->certs[indx].cert_list_length,
             cred->certs[indx].ocsp_data,
             cred->certs[indx].ocsp_data_length,
             cred->certs[indx].pkey, 0,
             NULL, NULL);
    } else {
      selected_certs_set(session, NULL, 0, NULL, 0,
             NULL, 0, NULL, NULL);
    }

    result = 0;
  }

 cleanup:
  gnutls_free(issuers_dn);
  return result;

}

/* Generate certificate message
 */
static int gen_x509_crt(gnutls_session_t session, gnutls_buffer_st * data)
{
  int ret, i;
  gnutls_pcert_st *apr_cert_list;
  gnutls_privkey_t apr_pkey;
  int apr_cert_list_length;
  unsigned init_pos = data->length;

  /* find the appropriate certificate
   */
  if ((ret =
       _gnutls_get_selected_cert(session, &apr_cert_list,
               &apr_cert_list_length, &apr_pkey)) < 0) {
    gnutls_assert();
    return ret;
  }

  ret = 3;
  for (i = 0; i < apr_cert_list_length; i++) {
    ret += apr_cert_list[i].cert.size + 3;
    /* hold size
     * for uint24 */
  }

  /* if no certificates were found then send:
   * 0B 00 00 03 00 00 00    // Certificate with no certs
   * instead of:
   * 0B 00 00 00    // empty certificate handshake
   *
   * ( the above is the whole handshake message, not
   * the one produced here )
   */

  ret = _gnutls_buffer_append_prefix(data, 24, ret - 3);
  if (ret < 0)
    return gnutls_assert_val(ret);

  for (i = 0; i < apr_cert_list_length; i++) {
    ret =
        _gnutls_buffer_append_data_prefix(data, 24,
                  apr_cert_list[i].
                  cert.data,
                  apr_cert_list[i].
                  cert.size);
    if (ret < 0)
      return gnutls_assert_val(ret);
  }

  return data->length - init_pos;
}

/* Generates a Raw Public Key certificate message that holds only the
 * SubjectPublicKeyInfo part of a regular certificate message.
 *
 * Returns the number of bytes sent or a negative error code.
 */
int _gnutls_gen_rawpk_crt(gnutls_session_t session, gnutls_buffer_st * data)
{
  int ret;
  gnutls_pcert_st *apr_cert_list;
  gnutls_privkey_t apr_pkey;
  int apr_cert_list_length;

  if ((ret = _gnutls_get_selected_cert(session, &apr_cert_list,
               &apr_cert_list_length,
               &apr_pkey)) < 0) {
    return gnutls_assert_val(ret);
  }

  /* Since we are transmitting a raw public key with no additional
   * certificate credentials attached to it, it doesn't make sense to
   * have more than one certificate set (i.e. to have a certificate chain).
   */
  assert(apr_cert_list_length <= 1);

  /* Write our certificate containing only the SubjectPublicKeyInfo to
   * the output buffer. We always have exactly one certificate that
   * contains our raw public key. Our message looks like:
   * <length++certificate> where
   * length = 3 bytes (or 24 bits) and
   * certificate = length bytes.
   */
  if (apr_cert_list_length == 0) {
    ret = _gnutls_buffer_append_prefix(data, 24, 0);
  } else {
    ret = _gnutls_buffer_append_data_prefix(data, 24,
              apr_cert_list[0].
              cert.data,
              apr_cert_list[0].
              cert.size);
  }

  if (ret < 0)
    return gnutls_assert_val(ret);

  return data->length;
}

int
_gnutls_gen_cert_client_crt(gnutls_session_t session, gnutls_buffer_st * data)
{
  gnutls_certificate_type_t cert_type;

  // Retrieve the (negotiated) certificate type for the client
  cert_type = get_certificate_type(session, GNUTLS_CTYPE_CLIENT);

  switch (cert_type) {
  case GNUTLS_CRT_X509:
    return gen_x509_crt(session, data);
  case GNUTLS_CRT_RAWPK:
    return _gnutls_gen_rawpk_crt(session, data);
  default:
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
  }
}

int
_gnutls_gen_cert_server_crt(gnutls_session_t session, gnutls_buffer_st * data)
{
  gnutls_certificate_type_t cert_type;

  // Retrieve the (negotiated) certificate type for the server
  cert_type = get_certificate_type(session, GNUTLS_CTYPE_SERVER);

  switch (cert_type) {
  case GNUTLS_CRT_X509:
    return gen_x509_crt(session, data);
  case GNUTLS_CRT_RAWPK:
    return _gnutls_gen_rawpk_crt(session, data);
  default:
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
  }
}

static
int check_pk_compat(gnutls_session_t session, gnutls_pubkey_t pubkey)
{
  unsigned cert_pk;
  unsigned kx;

  if (session->security_parameters.entity != GNUTLS_CLIENT)
    return 0;

  cert_pk = gnutls_pubkey_get_pk_algorithm(pubkey, NULL);
  if (cert_pk == GNUTLS_PK_UNKNOWN) {
    gnutls_assert();
    return GNUTLS_E_CERTIFICATE_ERROR;
  }

  kx = session->security_parameters.cs->kx_algorithm;

  if (_gnutls_map_kx_get_cred(kx, 1) == GNUTLS_CRD_CERTIFICATE &&
      !_gnutls_kx_supports_pk(kx, cert_pk)) {
    gnutls_assert();
    return GNUTLS_E_CERTIFICATE_ERROR;
  }

  return 0;
}

/* Process server certificate
 */
#define CLEAR_CERTS for(x=0;x<peer_certificate_list_size;x++) gnutls_pcert_deinit(&peer_certificate_list[x])
static int
_gnutls_proc_x509_crt(gnutls_session_t session,
          uint8_t * data, size_t data_size)
{
  int size, len, ret;
  uint8_t *p = data;
  cert_auth_info_t info;
  gnutls_certificate_credentials_t cred;
  ssize_t dsize = data_size;
  int i;
  gnutls_pcert_st *peer_certificate_list;
  size_t peer_certificate_list_size = 0, j, x;
  gnutls_datum_t tmp;

  cred = (gnutls_certificate_credentials_t)
      _gnutls_get_cred(session, GNUTLS_CRD_CERTIFICATE);
  if (cred == NULL) {
    gnutls_assert();
    return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
  }

  if ((ret =
       _gnutls_auth_info_init(session, GNUTLS_CRD_CERTIFICATE,
            sizeof(cert_auth_info_st), 1)) < 0) {
    gnutls_assert();
    return ret;
  }

  info = _gnutls_get_auth_info(session, GNUTLS_CRD_CERTIFICATE);
  if (unlikely(!info)) {
    gnutls_assert();
    return ret;
  }

  if (data == NULL || data_size == 0) {
    gnutls_assert();
    /* no certificate was sent */
    return GNUTLS_E_NO_CERTIFICATE_FOUND;
  }

  DECR_LEN(dsize, 3);
  size = _gnutls_read_uint24(p);
  p += 3;

  /* ensure no discrepancy in data */
  if (size != dsize)
    return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

  /* some implementations send 0B 00 00 06 00 00 03 00 00 00
   * instead of just 0B 00 00 03 00 00 00 as an empty certificate message.
   */
  if (size == 0 || (size == 3 && memcmp(p, "\x00\x00\x00", 3) == 0)) {
    gnutls_assert();
    /* no certificate was sent */
    return GNUTLS_E_NO_CERTIFICATE_FOUND;
  }

  i = dsize;
  while (i > 0) {
    DECR_LEN(dsize, 3);
    len = _gnutls_read_uint24(p);
    p += 3;
    DECR_LEN(dsize, len);
    peer_certificate_list_size++;
    p += len;
    i -= len + 3;
  }

  if (dsize != 0)
    return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

  if (peer_certificate_list_size == 0) {
    gnutls_assert();
    return GNUTLS_E_NO_CERTIFICATE_FOUND;
  }

  /* Ok we now allocate the memory to hold the
   * certificate list
   */

  peer_certificate_list =
      gnutls_calloc(1,
        sizeof(gnutls_pcert_st) *
        (peer_certificate_list_size));
  if (peer_certificate_list == NULL) {
    gnutls_assert();
    return GNUTLS_E_MEMORY_ERROR;
  }

  p = data + 3;

  /* Now we start parsing the list (again).
   * We don't use DECR_LEN since the list has
   * been parsed before.
   */

  for (j = 0; j < peer_certificate_list_size; j++) {
    len = _gnutls_read_uint24(p);
    p += 3;

    tmp.size = len;
    tmp.data = p;

    ret =
        gnutls_pcert_import_x509_raw(&peer_certificate_list
             [j], &tmp,
             GNUTLS_X509_FMT_DER, 0);
    if (ret < 0) {
      gnutls_assert();
      peer_certificate_list_size = j;
      ret = GNUTLS_E_CERTIFICATE_ERROR;
      goto cleanup;
    }

    p += len;
  }

  ret = check_pk_compat(session, peer_certificate_list[0].pubkey);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

  ret =
      _gnutls_pcert_to_auth_info(info,
               peer_certificate_list,
               peer_certificate_list_size);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

  return 0;

 cleanup:
  CLEAR_CERTS;
  gnutls_free(peer_certificate_list);
  return ret;

}

int _gnutls_proc_rawpk_crt(gnutls_session_t session,
         uint8_t * data, size_t data_size)
{
  int cert_size, ret;
  cert_auth_info_t info;
  gnutls_pcert_st *peer_certificate;
  gnutls_datum_t tmp_cert;

  uint8_t *p = data;
  ssize_t dsize = data_size;

  /* We assume data != null and data_size > 0 because
   * the caller checks this for us. */

  /* Read the length of our certificate. We always have exactly
   * one certificate that contains our raw public key. Our message
   * looks like:
   * <length++certificate> where
   * length = 3 bytes and
   * certificate = length bytes.
   */
  DECR_LEN(dsize, 3);
  cert_size = _gnutls_read_uint24(p);
  p += 3;

  /* Ensure no discrepancy in data */
  if (cert_size != dsize)
    return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

  if (cert_size == 0) {
    // No certificate was sent. This is not OK.
    return gnutls_assert_val(GNUTLS_E_NO_CERTIFICATE_FOUND);
  }

  DECR_LEN_FINAL(dsize, cert_size);

  /* We are now going to read our certificate and store it into
   * the authentication info structure.
   */
  tmp_cert.size = cert_size;
  tmp_cert.data = p;

  peer_certificate = gnutls_calloc(1, sizeof(*peer_certificate));
  if (peer_certificate == NULL) {
    return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);
  }
  // Import our raw certificate holding only a raw public key into this pcert
  ret =
      gnutls_pcert_import_rawpk_raw(peer_certificate, &tmp_cert,
            GNUTLS_X509_FMT_DER, 0, 0);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }
  // Check whether the PK algo is compatible with the negotiated KX
  ret = check_pk_compat(session, peer_certificate->pubkey);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

  ret = _gnutls_auth_info_init(session, GNUTLS_CRD_CERTIFICATE,
             sizeof(cert_auth_info_st), 1);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

  info = _gnutls_get_auth_info(session, GNUTLS_CRD_CERTIFICATE);
  if (unlikely(!info)) {
    gnutls_assert();
    goto cleanup;
  }

  /* Copy our imported certificate into the auth info structure
   * and free our temporary cert storage peer_certificate.
   */
  ret = _gnutls_pcert_to_auth_info(info, peer_certificate, 1);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

  return GNUTLS_E_SUCCESS;

 cleanup:
  if (peer_certificate != NULL) {
    gnutls_pcert_deinit(peer_certificate);
    gnutls_free(peer_certificate);
  }

  return ret;
}

int _gnutls_proc_crt(gnutls_session_t session, uint8_t * data, size_t data_size)
{
  gnutls_certificate_credentials_t cred;
  gnutls_certificate_type_t cert_type;

  cred =
      (gnutls_certificate_credentials_t) _gnutls_get_cred(session,
                GNUTLS_CRD_CERTIFICATE);
  if (cred == NULL) {
    gnutls_assert();
    return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
  }

  /* Determine what certificate type we need to process.
   * We need to process the certificate of the peer. */
  cert_type = get_certificate_type(session, GNUTLS_CTYPE_PEERS);

  switch (cert_type) {
  case GNUTLS_CRT_X509:
    return _gnutls_proc_x509_crt(session, data, data_size);
  case GNUTLS_CRT_RAWPK:
    return _gnutls_proc_rawpk_crt(session, data, data_size);
  default:
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
  }
}

/* Checks if we support the given signature algorithm
 * (RSA or DSA). Returns the corresponding gnutls_pk_algorithm_t
 * if true;
 */
inline static int _gnutls_check_supported_sign_algo(CertificateSigType algo)
{
  switch (algo) {
  case RSA_SIGN:
    return GNUTLS_PK_RSA;
  case DSA_SIGN:
    return GNUTLS_PK_DSA;
  case ECDSA_SIGN:
    return GNUTLS_PK_EC;
#ifdef ENABLE_GOST
  case GOSTR34102012_256_SIGN:
    return GNUTLS_PK_GOST_12_256;
  case GOSTR34102012_512_SIGN:
    return GNUTLS_PK_GOST_12_512;
#endif
  }

  return -1;
}

int
_gnutls_proc_cert_cert_req(gnutls_session_t session, uint8_t * data,
         size_t data_size)
{
  int size, ret;
  uint8_t *p;
  gnutls_certificate_credentials_t cred;
  ssize_t dsize;
  int i;
  gnutls_pk_algorithm_t pk_algos[MAX_CLIENT_SIGN_ALGOS];
  int pk_algos_length;
  const version_entry_st *ver = get_version(session);

  if (unlikely(ver == NULL))
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  cred = (gnutls_certificate_credentials_t)
      _gnutls_get_cred(session, GNUTLS_CRD_CERTIFICATE);
  if (cred == NULL) {
    gnutls_assert();
    return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
  }

  if ((ret =
       _gnutls_auth_info_init(session, GNUTLS_CRD_CERTIFICATE,
            sizeof(cert_auth_info_st), 0)) < 0) {
    gnutls_assert();
    return ret;
  }

  p = data;
  dsize = data_size;

  DECR_LEN(dsize, 1);
  size = p[0];
  p++;
  /* check if the sign algorithm is supported.
   */
  pk_algos_length = 0;
  for (i = 0; i < size; i++, p++) {
    DECR_LEN(dsize, 1);
    if ((ret = _gnutls_check_supported_sign_algo(*p)) > 0) {
      if (pk_algos_length < MAX_CLIENT_SIGN_ALGOS) {
        pk_algos[pk_algos_length++] = ret;
      }
    }
  }

  if (pk_algos_length == 0) {
    gnutls_assert();
    return GNUTLS_E_UNKNOWN_PK_ALGORITHM;
  }

  if (_gnutls_version_has_selectable_sighash(ver)) {
    /* read supported hashes */
    int hash_num;
    DECR_LEN(dsize, 2);
    hash_num = _gnutls_read_uint16(p);
    p += 2;
    DECR_LEN(dsize, hash_num);

    ret = _gnutls_sign_algorithm_parse_data(session, p, hash_num);
    if (ret < 0) {
      gnutls_assert();
      return ret;
    }

    p += hash_num;
  }

  /* read the certificate authorities */
  DECR_LEN(dsize, 2);
  size = _gnutls_read_uint16(p);
  p += 2;

  DECR_LEN_FINAL(dsize, size);

  /* We should reply with a certificate message,
   * even if we have no certificate to send.
   */
  session->internals.hsk_flags |= HSK_CRT_ASKED;

  /* now we ask the user to tell which one
   * he wants to use.
   */
  if ((ret =
       _gnutls_select_client_cert(session, p, size, pk_algos,
          pk_algos_length)) < 0) {
    gnutls_assert();
    return ret;
  }

  return 0;
}

int
_gnutls_gen_cert_client_crt_vrfy(gnutls_session_t session,
         gnutls_buffer_st * data)
{
  int ret;
  gnutls_pcert_st *apr_cert_list;
  gnutls_privkey_t apr_pkey;
  int apr_cert_list_length;
  gnutls_datum_t signature = { NULL, 0 };
  gnutls_sign_algorithm_t sign_algo;
  const version_entry_st *ver = get_version(session);
  unsigned init_pos = data->length;

  if (unlikely(ver == NULL))
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  /* find the appropriate certificate */
  if ((ret =
       _gnutls_get_selected_cert(session, &apr_cert_list,
               &apr_cert_list_length, &apr_pkey)) < 0) {
    gnutls_assert();
    return ret;
  }

  if (apr_cert_list_length > 0) {
    if ((ret =
         _gnutls_handshake_sign_crt_vrfy(session,
                 &apr_cert_list[0],
                 apr_pkey,
                 &signature)) < 0) {
      gnutls_assert();
      return ret;
    }
    sign_algo = ret;
  } else {
    return 0;
  }

  if (_gnutls_version_has_selectable_sighash(ver)) {
    const sign_algorithm_st *aid;
    uint8_t p[2];
    /* error checking is not needed here since we have used those algorithms */
    aid = _gnutls_sign_to_tls_aid(sign_algo);
    if (aid == NULL)
      return gnutls_assert_val(GNUTLS_E_UNKNOWN_ALGORITHM);

    p[0] = aid->id[0];
    p[1] = aid->id[1];
    ret = _gnutls_buffer_append_data(data, p, 2);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }
  }

  ret =
      _gnutls_buffer_append_data_prefix(data, 16, signature.data,
                signature.size);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

  ret = data->length - init_pos;

 cleanup:
  _gnutls_free_datum(&signature);
  return ret;
}

int
_gnutls_proc_cert_client_crt_vrfy(gnutls_session_t session,
          uint8_t * data, size_t data_size)
{
  int size, ret;
  ssize_t dsize = data_size;
  uint8_t *pdata = data;
  gnutls_datum_t sig;
  cert_auth_info_t info =
      _gnutls_get_auth_info(session, GNUTLS_CRD_CERTIFICATE);
  gnutls_pcert_st peer_cert;
  gnutls_sign_algorithm_t sign_algo = GNUTLS_SIGN_UNKNOWN;
  const version_entry_st *ver = get_version(session);
  gnutls_certificate_credentials_t cred;
  unsigned vflags;

  if (unlikely(info == NULL || info->ncerts == 0 || ver == NULL)) {
    gnutls_assert();
    /* we need this in order to get peer's certificate */
    return GNUTLS_E_INTERNAL_ERROR;
  }

  cred = (gnutls_certificate_credentials_t)
      _gnutls_get_cred(session, GNUTLS_CRD_CERTIFICATE);
  if (cred == NULL) {
    gnutls_assert();
    return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
  }

  vflags =
      cred->verify_flags | session->internals.additional_verify_flags;

  if (_gnutls_version_has_selectable_sighash(ver)) {
    DECR_LEN(dsize, 2);

    sign_algo = _gnutls_tls_aid_to_sign(pdata[0], pdata[1], ver);
    if (sign_algo == GNUTLS_SIGN_UNKNOWN) {
      gnutls_assert();
      return GNUTLS_E_UNSUPPORTED_SIGNATURE_ALGORITHM;
    }
    pdata += 2;
  }

  ret = _gnutls_session_sign_algo_enabled(session, sign_algo);
  if (ret < 0)
    return
        gnutls_assert_val(GNUTLS_E_UNSUPPORTED_SIGNATURE_ALGORITHM);

  DECR_LEN(dsize, 2);
  size = _gnutls_read_uint16(pdata);
  pdata += 2;

  DECR_LEN_FINAL(dsize, size);

  sig.data = pdata;
  sig.size = size;

  ret = _gnutls_get_auth_info_pcert(&peer_cert,
            session->security_parameters.
            client_ctype, info);

  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  if ((ret =
       _gnutls_handshake_verify_crt_vrfy(session, vflags, &peer_cert,
                 &sig, sign_algo)) < 0) {
    gnutls_assert();
    gnutls_pcert_deinit(&peer_cert);
    return ret;
  }
  gnutls_pcert_deinit(&peer_cert);

  return 0;
}

int
_gnutls_gen_cert_server_cert_req(gnutls_session_t session,
         gnutls_buffer_st * data)
{
  gnutls_certificate_credentials_t cred;
  int ret, i;
  uint8_t tmp_data[CERTTYPE_SIZE];
  const version_entry_st *ver = get_version(session);
  unsigned init_pos = data->length;
  enum CertificateSigTypeFlags flags;

  if (unlikely(ver == NULL))
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  /* Now we need to generate the RDN sequence. This is
   * already in the CERTIFICATE_CRED structure, to improve
   * performance.
   */

  cred = (gnutls_certificate_credentials_t)
      _gnutls_get_cred(session, GNUTLS_CRD_CERTIFICATE);
  if (cred == NULL) {
    gnutls_assert();
    return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
  }

  if (_gnutls_version_has_selectable_sighash(ver)) {
    size_t j;

    flags = 0;
    for (j = 0; j < session->internals.priorities->sigalg.size; j++) {
      const gnutls_sign_entry_st *se =
          session->internals.priorities->sigalg.entry[j];
      switch (se->pk) {
      case GNUTLS_PK_RSA:
      case GNUTLS_PK_RSA_PSS:
        flags |= RSA_SIGN_FLAG;
        break;
      case GNUTLS_PK_DSA:
        flags |= DSA_SIGN_FLAG;
        break;
      case GNUTLS_PK_ECDSA:
        flags |= ECDSA_SIGN_FLAG;
        break;
#ifdef ENABLE_GOST
      case GNUTLS_PK_GOST_12_256:
        flags |= GOSTR34102012_256_SIGN_FLAG;
        break;
      case GNUTLS_PK_GOST_12_512:
        flags |= GOSTR34102012_512_SIGN_FLAG;
        break;
#endif
      default:
        gnutls_assert();
        _gnutls_debug_log
            ("%s is unsupported for cert request\n",
             gnutls_pk_get_name(se->pk));
      }
    }

  } else {
#ifdef ENABLE_GOST
    if (_gnutls_kx_is_vko_gost
        (session->security_parameters.cs->kx_algorithm)) {
      flags =
          GOSTR34102012_256_SIGN_FLAG |
          GOSTR34102012_512_SIGN_FLAG;
    } else
#endif
    {
      flags = RSA_SIGN_FLAG | DSA_SIGN_FLAG | ECDSA_SIGN_FLAG;
    }
  }

  i = 1;
  if (flags & RSA_SIGN_FLAG) {
    tmp_data[i++] = RSA_SIGN;
  }
  if (flags & DSA_SIGN_FLAG) {
    tmp_data[i++] = DSA_SIGN;
  }
  if (flags & ECDSA_SIGN_FLAG) {
    tmp_data[i++] = ECDSA_SIGN;
  }
#ifdef ENABLE_GOST
  if (flags & GOSTR34102012_256_SIGN_FLAG) {
    tmp_data[i++] = GOSTR34102012_256_SIGN;
  }
  if (flags & GOSTR34102012_512_SIGN_FLAG) {
    tmp_data[i++] = GOSTR34102012_512_SIGN;
  }
#endif
  tmp_data[0] = i - 1;

  ret = _gnutls_buffer_append_data(data, tmp_data, i);
  if (ret < 0)
    return gnutls_assert_val(ret);

  if (_gnutls_version_has_selectable_sighash(ver)) {
    ret = _gnutls_sign_algorithm_write_params(session, data);
    if (ret < 0) {
      gnutls_assert();
      return ret;
    }
  }

  if (session->security_parameters.client_ctype == GNUTLS_CRT_X509 &&
      session->internals.ignore_rdn_sequence == 0) {

    ret =
        _gnutls_buffer_append_data_prefix(data, 16,
                  cred->
                  tlist->x509_rdn_sequence.
                  data,
                  cred->
                  tlist->x509_rdn_sequence.
                  size);
    if (ret < 0)
      return gnutls_assert_val(ret);
  } else {
    ret = _gnutls_buffer_append_prefix(data, 16, 0);
    if (ret < 0)
      return gnutls_assert_val(ret);
  }

  return data->length - init_pos;
}

/* This function will return the appropriate certificate to use.
 * Fills in the apr_cert_list, apr_cert_list_length and apr_pkey.
 * The return value is a negative error code on error.
 *
 * It is normal to return 0 with no certificates in client side.
 *
 */
int
_gnutls_get_selected_cert(gnutls_session_t session,
        gnutls_pcert_st ** apr_cert_list,
        int *apr_cert_list_length,
        gnutls_privkey_t * apr_pkey)
{
  if (session->security_parameters.entity == GNUTLS_SERVER) {

    *apr_cert_list = session->internals.selected_cert_list;
    *apr_pkey = session->internals.selected_key;
    *apr_cert_list_length =
        session->internals.selected_cert_list_length;

    if (*apr_cert_list_length == 0 || *apr_cert_list == NULL) {
      gnutls_assert();
      return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
    }

  } else {   /* CLIENT SIDE */
    /* _gnutls_select_client_cert() must have been called before.
     */
    *apr_cert_list = session->internals.selected_cert_list;
    *apr_cert_list_length =
        session->internals.selected_cert_list_length;
    *apr_pkey = session->internals.selected_key;

  }

  return 0;
}

void _gnutls_selected_certs_deinit(gnutls_session_t session)
{
  if (session->internals.selected_need_free != 0) {
    int i;

    for (i = 0;
         i < session->internals.selected_cert_list_length; i++) {
      gnutls_pcert_deinit(&session->internals.
              selected_cert_list[i]);
    }
    gnutls_free(session->internals.selected_cert_list);

    for (i = 0; i < session->internals.selected_ocsp_length; i++) {
      _gnutls_free_datum(&session->internals.
             selected_ocsp[i].response);
    }
    gnutls_free(session->internals.selected_ocsp);

    gnutls_privkey_deinit(session->internals.selected_key);
  }
  session->internals.selected_ocsp_func = NULL;

  session->internals.selected_cert_list = NULL;
  session->internals.selected_cert_list_length = 0;

  session->internals.selected_key = NULL;

  return;
}

static void
selected_certs_set(gnutls_session_t session,
       gnutls_pcert_st * certs, int ncerts,
       gnutls_ocsp_data_st * ocsp, unsigned nocsp,
       gnutls_privkey_t key, int need_free,
       gnutls_status_request_ocsp_func ocsp_func,
       void *ocsp_func_ptr)
{
  _gnutls_selected_certs_deinit(session);

  session->internals.selected_cert_list = certs;
  session->internals.selected_cert_list_length = ncerts;

  session->internals.selected_ocsp = ocsp;
  session->internals.selected_ocsp_length = nocsp;

  session->internals.selected_key = key;
  session->internals.selected_need_free = need_free;

  session->internals.selected_ocsp_func = ocsp_func;
  session->internals.selected_ocsp_func_ptr = ocsp_func_ptr;
}

static void get_server_name(gnutls_session_t session, uint8_t * name,
          size_t max_name_size)
{
  int ret, i;
  size_t max_name;
  unsigned int type;

  ret = 0;
  for (i = 0; !(ret < 0); i++) {
    max_name = max_name_size;
    ret =
        gnutls_server_name_get(session, name, &max_name, &type, i);
    if (ret >= 0 && type == GNUTLS_NAME_DNS)
      return;
  }

  name[0] = 0;

  return;
}

/* Checks the compatibility of the pubkey in the certificate with the
 * ciphersuite and selects a signature algorithm (if required by the
 * ciphersuite and TLS version) appropriate for the certificate. If none
 * can be selected returns an error.
 *
 * IMPORTANT
 * Currently this function is only called from _gnutls_select_server_cert,
 * i.e. it is only called at the server. We therefore retrieve the
 * negotiated server certificate type within this function.
 * If, in the future, this routine is called at the client then we
 * need to adapt the implementation accordingly.
 */
static
int cert_select_sign_algorithm(gnutls_session_t session,
             gnutls_pcert_st * cert,
             gnutls_privkey_t pkey,
             const gnutls_cipher_suite_entry_st * cs)
{
  gnutls_pubkey_t pubkey = cert->pubkey;
  gnutls_certificate_type_t cert_type = cert->type;
  unsigned pk = pubkey->params.algo;
  unsigned key_usage;
  gnutls_sign_algorithm_t algo;
  const version_entry_st *ver = get_version(session);
  gnutls_certificate_type_t ctype;

  assert(IS_SERVER(session));

  /* Retrieve the server certificate type */
  ctype = get_certificate_type(session, GNUTLS_CTYPE_SERVER);

  if (ctype != cert_type) {
    return gnutls_assert_val(GNUTLS_E_INSUFFICIENT_CREDENTIALS);
  }

  key_usage = get_key_usage(session, pubkey);

  /* In TLS1.3 we support only signatures; ensure the selected key supports them */
  if (ver->tls13_sem
      && _gnutls_check_key_usage_for_sig(session, key_usage, 1) < 0)
    return gnutls_assert_val(GNUTLS_E_INSUFFICIENT_CREDENTIALS);

  if (!ver->tls13_sem
      && !_gnutls_kx_supports_pk_usage(cs->kx_algorithm, pk, key_usage)) {
    return gnutls_assert_val(GNUTLS_E_INSUFFICIENT_CREDENTIALS);
  }

  if (!ver->tls13_sem
      && _gnutls_kx_encipher_type(cs->kx_algorithm) != CIPHER_SIGN)
    return 0;

  if (!_gnutls_version_has_selectable_sighash(ver)) {
    /* For SSL3.0 and TLS1.0 we lie as we cannot express md5-sha1 as
     * signature algorithm. */
    algo =
        gnutls_pk_to_sign(cert->pubkey->params.algo,
              GNUTLS_DIG_SHA1);
    gnutls_sign_algorithm_set_server(session, algo);
    return 0;
  }

  algo =
      _gnutls_session_get_sign_algo(session, cert, pkey, 0,
            cs->kx_algorithm);
  if (algo == GNUTLS_SIGN_UNKNOWN)
    return gnutls_assert_val(GNUTLS_E_INCOMPATIBLE_SIG_WITH_KEY);

  gnutls_sign_algorithm_set_server(session, algo);
  _gnutls_handshake_log("Selected signature algorithm: %s\n",
            gnutls_sign_algorithm_get_name(algo));

  return 0;
}

/* finds the most appropriate certificate in the cert list.
 * The 'appropriate' is defined by the user.
 *
 * requested_algo holds the parameters required by the peer (RSA, DSA
 * or -1 for any).
 *
 * Returns 0 on success and a negative error code on error. The
 * selected certificate will be in session->internals.selected_*.
 *
 */
int
_gnutls_select_server_cert(gnutls_session_t session,
         const gnutls_cipher_suite_entry_st * cs)
{
  unsigned i, j;
  int idx, ret;
  gnutls_certificate_credentials_t cred;
  char server_name[MAX_CN];

  cred = (gnutls_certificate_credentials_t)
      _gnutls_get_cred(session, GNUTLS_CRD_CERTIFICATE);
  if (cred == NULL) {
    gnutls_assert(); /* we don't need to select a cert */
    return 0;
  }

  /* When a callback is set, we call it once to get the
   * certificate and then check its compatibility with
   * the ciphersuites.
   */
  if (cred->get_cert_callback3) {
    if (session->internals.selected_cert_list_length == 0) {
      ret = call_get_cert_callback(session, NULL, 0, NULL, 0);
      if (ret < 0)
        return gnutls_assert_val(ret);

      if (session->internals.selected_cert_list_length == 0)
        return
            gnutls_assert_val
            (GNUTLS_E_INSUFFICIENT_CREDENTIALS);

      if (unlikely
          (session->internals.selected_cert_list == NULL)) {
        return
            gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
      }

      _gnutls_debug_log("Selected (%s) cert\n",
            gnutls_pk_get_name(session->
                   internals.selected_cert_list
                   [0].pubkey->
                   params.algo));
    }

    if (session->internals.selected_key == NULL)
      return
          gnutls_assert_val
          (GNUTLS_E_INSUFFICIENT_CREDENTIALS);

    ret = cert_select_sign_algorithm(session,
             &session->
             internals.selected_cert_list
             [0],
             session->
             internals.selected_key, cs);
    if (ret < 0)
      return gnutls_assert_val(ret);

    return 0;
  }

  /* Otherwise... we check the compatibility of the ciphersuite
   * with all the certificates available. */

  get_server_name(session, (unsigned char *)server_name,
      sizeof(server_name));

  _gnutls_handshake_log("HSK[%p]: Requested server name: '%s'\n",
            session, server_name);
  idx = -1;   /* default is use no certificate */

  /* find certificates that match the requested server_name
   */

  if (server_name[0] != 0) {
    for (j = 0; j < cred->ncerts; j++) {
      i = cred->sorted_cert_idx[j];

      if (cred->certs[i].names != NULL
          && _gnutls_str_array_match(cred->certs[i].names,
                   server_name) != 0) {
        /* if requested algorithms are also compatible select it */

        ret = cert_select_sign_algorithm(session,
                 &cred->certs
                 [i].cert_list
                 [0],
                 cred->
                 certs[i].pkey,
                 cs);
        if (ret >= 0) {
          idx = i;
          _gnutls_debug_log
              ("Selected (%s) cert based on ciphersuite %x.%x: %s\n",
               gnutls_pk_get_name(cred->certs
                [i].cert_list
                [0].pubkey->
                params.algo),
               (unsigned)cs->id[0],
               (unsigned)cs->id[1], cs->name);
          /* found */
          goto finished;
        }
      }
    }
  }

  /* no name match */
  for (j = 0; j < cred->ncerts; j++) {
    i = cred->sorted_cert_idx[j];

    _gnutls_handshake_log
        ("HSK[%p]: checking compat of %s with certificate[%d] (%s/%s)\n",
         session, cs->name, i,
         gnutls_pk_get_name(cred->certs[i].cert_list[0].pubkey->
          params.algo),
         gnutls_certificate_type_get_name(cred->certs[i].
                  cert_list[0].type));

    ret = cert_select_sign_algorithm(session,
             &cred->certs[i].cert_list[0],
             cred->certs[i].pkey, cs);
    if (ret >= 0) {
      idx = i;
      _gnutls_debug_log
          ("Selected (%s) cert based on ciphersuite %x.%x: %s\n",
           gnutls_pk_get_name(cred->certs[i].
            cert_list[0].pubkey->params.
            algo), (unsigned)cs->id[0],
           (unsigned)cs->id[1], cs->name);
      /* found */
      goto finished;
    }
  }

  /* store the certificate pointer for future use, in the handshake.
   * (This will allow not calling this callback again.)
   */
 finished:
  if (idx >= 0) {
    gnutls_status_request_ocsp_func ocsp_func = NULL;
    void *ocsp_ptr = NULL;
    gnutls_ocsp_data_st *ocsp = NULL;
    unsigned nocsp = 0;

    if (cred->certs[idx].ocsp_data_length > 0) {
      ocsp = &cred->certs[idx].ocsp_data[0];
      nocsp = cred->certs[idx].ocsp_data_length;
    } else if (cred->glob_ocsp_func != NULL) {
      ocsp_func = cred->glob_ocsp_func;
      ocsp_ptr = cred->glob_ocsp_func_ptr;
    } else if (cred->certs[idx].ocsp_func != NULL) {
      ocsp_func = cred->certs[idx].ocsp_func;
      ocsp_ptr = cred->certs[idx].ocsp_func_ptr;
    }

    selected_certs_set(session,
           &cred->certs[idx].cert_list[0],
           cred->certs[idx].cert_list_length,
           ocsp, nocsp,
           cred->certs[idx].pkey, 0,
           ocsp_func, ocsp_ptr);
  } else {
    /* Certificate does not support REQUESTED_ALGO.  */
    return gnutls_assert_val(GNUTLS_E_INSUFFICIENT_CREDENTIALS);
  }

  return 0;
}

int _gnutls_gen_dhe_signature(gnutls_session_t session,
            gnutls_buffer_st * data, uint8_t * plain,
            unsigned plain_size)
{
  gnutls_pcert_st *apr_cert_list;
  gnutls_privkey_t apr_pkey;
  int apr_cert_list_length;
  gnutls_datum_t signature = { NULL, 0 }, ddata;
  gnutls_sign_algorithm_t sign_algo;
  const version_entry_st *ver = get_version(session);
  int ret;

  if (unlikely(ver == NULL))
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  ddata.data = plain;
  ddata.size = plain_size;

  /* find the appropriate certificate */
  if ((ret =
       _gnutls_get_selected_cert(session, &apr_cert_list,
               &apr_cert_list_length, &apr_pkey)) < 0) {
    gnutls_assert();
    return ret;
  }

  if (apr_cert_list_length > 0) {
    if ((ret =
         _gnutls_handshake_sign_data(session,
             &apr_cert_list[0],
             apr_pkey, &ddata,
             &signature, &sign_algo)) < 0) {
      gnutls_assert();
      goto cleanup;
    }
  } else {
    gnutls_assert();
    ret = 0;  /* ANON-DH, do not put a signature - ILLEGAL! */
    goto cleanup;
  }

  if (_gnutls_version_has_selectable_sighash(ver)) {
    const sign_algorithm_st *aid;
    uint8_t p[2];

    if (sign_algo == GNUTLS_SIGN_UNKNOWN) {
      ret = GNUTLS_E_UNKNOWN_ALGORITHM;
      goto cleanup;
    }

    aid = _gnutls_sign_to_tls_aid(sign_algo);
    if (aid == NULL) {
      gnutls_assert();
      ret = GNUTLS_E_UNKNOWN_ALGORITHM;
      goto cleanup;
    }

    p[0] = aid->id[0];
    p[1] = aid->id[1];

    ret = _gnutls_buffer_append_data(data, p, 2);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }
  }

  ret =
      _gnutls_buffer_append_data_prefix(data, 16, signature.data,
                signature.size);
  if (ret < 0) {
    gnutls_assert();
  }

  ret = 0;

 cleanup:
  _gnutls_free_datum(&signature);
  return ret;
}

int
_gnutls_proc_dhe_signature(gnutls_session_t session, uint8_t * data,
         size_t _data_size, gnutls_datum_t * vparams)
{
  int sigsize;
  gnutls_datum_t signature;
  int ret;
  cert_auth_info_t info =
      _gnutls_get_auth_info(session, GNUTLS_CRD_CERTIFICATE);
  ssize_t data_size = _data_size;
  gnutls_pcert_st peer_cert;
  gnutls_sign_algorithm_t sign_algo = GNUTLS_SIGN_UNKNOWN;
  const version_entry_st *ver = get_version(session);
  gnutls_certificate_credentials_t cred;
  unsigned vflags;
  gnutls_certificate_type_t cert_type;

  if (unlikely(info == NULL || info->ncerts == 0 || ver == NULL)) {
    gnutls_assert();
    /* we need this in order to get peer's certificate */
    return GNUTLS_E_INTERNAL_ERROR;
  }

  cred = (gnutls_certificate_credentials_t)
      _gnutls_get_cred(session, GNUTLS_CRD_CERTIFICATE);
  if (cred == NULL) {
    gnutls_assert();
    return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
  }

  vflags =
      cred->verify_flags | session->internals.additional_verify_flags;

  /* VERIFY SIGNATURE */
  if (_gnutls_version_has_selectable_sighash(ver)) {
    uint8_t id[2];

    DECR_LEN(data_size, 1);
    id[0] = *data++;
    DECR_LEN(data_size, 1);
    id[1] = *data++;

    sign_algo = _gnutls_tls_aid_to_sign(id[0], id[1], ver);
    if (sign_algo == GNUTLS_SIGN_UNKNOWN) {
      _gnutls_debug_log("unknown signature %d.%d\n",
            (int)id[0], (int)id[1]);
      gnutls_assert();
      return GNUTLS_E_UNSUPPORTED_SIGNATURE_ALGORITHM;
    }
  }
  DECR_LEN(data_size, 2);
  sigsize = _gnutls_read_uint16(data);
  data += 2;

  DECR_LEN_FINAL(data_size, sigsize);
  signature.data = data;
  signature.size = sigsize;

  // Retrieve the negotiated certificate type
  cert_type = get_certificate_type(session, GNUTLS_CTYPE_SERVER);

  if ((ret =
       _gnutls_get_auth_info_pcert(&peer_cert, cert_type, info)) < 0) {
    gnutls_assert();
    return ret;
  }

  ret =
      _gnutls_handshake_verify_data(session, vflags, &peer_cert, vparams,
            &signature, sign_algo);

  gnutls_pcert_deinit(&peer_cert);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  return 0;
}

Coverage Report

Created: 2023-03-26 07:33