7.3.6 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.

/* This example code is placed in the public domain. */

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

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <gnutls/gnutls.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 "/etc/ssl/certs/ca-certificates.crt"
#define MSG "GET / HTTP/1.0\r\n\r\n"

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;

	if (gnutls_check_version("3.1.4") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.1.4 or later is required for this example\n");
		exit(1);
	}

	/* for backwards compatibility with gnutls < 3.3.0 */
	gnutls_global_init();

	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_priority_set_direct(session, "NORMAL:+SRP:+SRP-RSA:+SRP-DSS",
				   NULL);

	/* 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_int(session, sd);
	gnutls_handshake_set_timeout(session, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);

	/* Perform the TLS handshake
	 */
	do {
		ret = gnutls_handshake(session);
	} while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

	if (ret < 0) {
		fprintf(stderr, "*** Handshake failed\n");
		gnutls_perror(ret);
		goto end;
	} else {
		char *desc;

		desc = gnutls_session_get_desc(session);
		printf("- Session info: %s\n", desc);
		gnutls_free(desc);
	}

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

	ret = gnutls_record_recv(session, buffer, MAX_BUF);
	if (gnutls_error_is_fatal(ret) != 0 || 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;
}