7.3.7 Simple client example with SRP authentication

The following client is a very simple SRP TLS client which connects to a server and authenticates using a username and a password. The server may authenticate itself using a certificate, and in that case it has to be verified.

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <gnutls/gnutls.h>
#include <gnutls/extra.h>

/* Those functions are defined in other examples.
 */
extern void check_alert (gnutls_session_t session, int ret);
extern int tcp_connect (void);
extern void tcp_close (int sd);

#define MAX_BUF 1024
#define USERNAME "user"
#define PASSWORD "pass"
#define CAFILE "ca.pem"
#define SA struct sockaddr
#define MSG "GET / HTTP/1.0\r\n\r\n"

const int kx_priority[] = { GNUTLS_KX_SRP, GNUTLS_KX_SRP_DSS,
  GNUTLS_KX_SRP_RSA, 0
};

int
main (void)
{
  int ret;
  int sd, ii;
  gnutls_session_t session;
  char buffer[MAX_BUF + 1];
  gnutls_srp_client_credentials_t srp_cred;
  gnutls_certificate_credentials_t cert_cred;

  gnutls_global_init ();

  /* now enable the gnutls-extra library which contains the
   * SRP stuff. 
   */
  gnutls_global_init_extra ();

  gnutls_srp_allocate_client_credentials (&srp_cred);
  gnutls_certificate_allocate_credentials (&cert_cred);

  gnutls_certificate_set_x509_trust_file (cert_cred, CAFILE,
					  GNUTLS_X509_FMT_PEM);
  gnutls_srp_set_client_credentials (srp_cred, USERNAME, PASSWORD);

  /* connects to server 
   */
  sd = tcp_connect ();

  /* Initialize TLS session 
   */
  gnutls_init (&session, GNUTLS_CLIENT);


  /* Set the priorities.
   */
  gnutls_set_default_priority (session);
  gnutls_kx_set_priority (session, kx_priority);


  /* put the SRP credentials to the current session
   */
  gnutls_credentials_set (session, GNUTLS_CRD_SRP, srp_cred);
  gnutls_credentials_set (session, GNUTLS_CRD_CERTIFICATE, cert_cred);

  gnutls_transport_set_ptr (session, (gnutls_transport_ptr_t) sd);

  /* Perform the TLS handshake
   */
  ret = gnutls_handshake (session);

  if (ret < 0)
    {
      fprintf (stderr, "*** Handshake failed\n");
      gnutls_perror (ret);
      goto end;
    }
  else
    {
      printf ("- Handshake was completed\n");
    }

  gnutls_record_send (session, MSG, strlen (MSG));

  ret = gnutls_record_recv (session, buffer, MAX_BUF);
  if (gnutls_error_is_fatal (ret) == 1 || ret == 0)
    {
      if (ret == 0)
	{
	  printf ("- Peer has closed the GNUTLS connection\n");
	  goto end;
	}
      else
	{
	  fprintf (stderr, "*** Error: %s\n", gnutls_strerror (ret));
	  goto end;
	}
    }
  else
    check_alert (session, ret);

  if (ret > 0)
    {
      printf ("- Received %d bytes: ", ret);
      for (ii = 0; ii < ret; ii++)
	{
	  fputc (buffer[ii], stdout);
	}
      fputs ("\n", stdout);
    }
  gnutls_bye (session, GNUTLS_SHUT_RDWR);

end:

  tcp_close (sd);

  gnutls_deinit (session);

  gnutls_srp_free_client_credentials (srp_cred);
  gnutls_certificate_free_credentials (cert_cred);

  gnutls_global_deinit ();

  return 0;
}