#include <stdio.h>
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>

/* This function will try to verify the peer's certificate, and
 * also check if the hostname matches, and the activation, expiration dates.
 */
void
verify_certificate (gnutls_session_t session, const char *hostname)
{
  unsigned int status;
  const gnutls_datum_t *cert_list;
  int cert_list_size, ret;
  gnutls_x509_crt_t cert;


  /* This verification function uses the trusted CAs in the credentials
   * structure. So you must have installed one or more CA certificates.
   */
  ret = gnutls_certificate_verify_peers2 (session, &status);

  if (ret < 0)
    {
      printf ("Error\n");
      return;
    }

  if (status & GNUTLS_CERT_INVALID)
    printf ("The certificate is not trusted.\n");

  if (status & GNUTLS_CERT_SIGNER_NOT_FOUND)
    printf ("The certificate hasn't got a known issuer.\n");

  if (status & GNUTLS_CERT_REVOKED)
    printf ("The certificate has been revoked.\n");


  /* Up to here the process is the same for X.509 certificates and
   * OpenPGP keys. From now on X.509 certificates are assumed. This can
   * be easily extended to work with openpgp keys as well.
   */
  if (gnutls_certificate_type_get (session) != GNUTLS_CRT_X509)
    return;

  if (gnutls_x509_crt_init (&cert) < 0)
    {
      printf ("error in initialization\n");
      return;
    }

  cert_list = gnutls_certificate_get_peers (session, &cert_list_size);
  if (cert_list == NULL)
    {
      printf ("No certificate was found!\n");
      return;
    }

  /* This is not a real world example, since we only check the first 
   * certificate in the given chain.
   */
  if (gnutls_x509_crt_import (cert, &cert_list[0], GNUTLS_X509_FMT_DER) < 0)
    {
      printf ("error parsing certificate\n");
      return;
    }

  /* Beware here we do not check for errors.
   */
  if (gnutls_x509_crt_get_expiration_time (cert) < time (0))
    {
      printf ("The certificate has expired\n");
      return;
    }

  if (gnutls_x509_crt_get_activation_time (cert) > time (0))
    {
      printf ("The certificate is not yet activated\n");
      return;
    }

  if (!gnutls_x509_crt_check_hostname (cert, hostname))
    {
      printf ("The certificate's owner does not match hostname '%s'\n",
	      hostname);
      return;
    }

  gnutls_x509_crt_deinit (cert);

  return;
}
