7.3.10 Echo server with SRP authentication

This is a server which supports SRP authentication. It is also possible to combine this functionality with a certificate server. Here it is separate for simplicity.

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

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

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <gnutls/gnutls.h>

#define SRP_PASSWD "tpasswd"
#define SRP_PASSWD_CONF "tpasswd.conf"

#define KEYFILE "key.pem"
#define CERTFILE "cert.pem"
#define CAFILE "/etc/ssl/certs/ca-certificates.crt"

#define LOOP_CHECK(rval, cmd) \
	do {                  \
		rval = cmd;   \
	} while (rval == GNUTLS_E_AGAIN || rval == GNUTLS_E_INTERRUPTED)

/* This is a sample TLS-SRP echo server.
 */

#define SOCKET_ERR(err, s)  \
	if (err == -1) {    \
		perror(s);  \
		return (1); \
	}
#define MAX_BUF 1024
#define PORT 5556 /* listen to 5556 port */

int main(void)
{
	int err, listen_sd;
	int sd, ret;
	struct sockaddr_in sa_serv;
	struct sockaddr_in sa_cli;
	socklen_t client_len;
	char topbuf[512];
	gnutls_session_t session;
	gnutls_srp_server_credentials_t srp_cred;
	gnutls_certificate_credentials_t cert_cred;
	char buffer[MAX_BUF + 1];
	int optval = 1;
	char name[256];

	strcpy(name, "Echo Server");

	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();

	/* SRP_PASSWD a password file (created with the included srptool utility) 
	 */
	gnutls_srp_allocate_server_credentials(&srp_cred);
	gnutls_srp_set_server_credentials_file(srp_cred, SRP_PASSWD,
					       SRP_PASSWD_CONF);

	gnutls_certificate_allocate_credentials(&cert_cred);
	gnutls_certificate_set_x509_trust_file(cert_cred, CAFILE,
					       GNUTLS_X509_FMT_PEM);
	gnutls_certificate_set_x509_key_file(cert_cred, CERTFILE, KEYFILE,
					     GNUTLS_X509_FMT_PEM);

	/* TCP socket operations
	 */
	listen_sd = socket(AF_INET, SOCK_STREAM, 0);
	SOCKET_ERR(listen_sd, "socket");

	memset(&sa_serv, '\0', sizeof(sa_serv));
	sa_serv.sin_family = AF_INET;
	sa_serv.sin_addr.s_addr = INADDR_ANY;
	sa_serv.sin_port = htons(PORT); /* Server Port number */

	setsockopt(listen_sd, SOL_SOCKET, SO_REUSEADDR, (void *)&optval,
		   sizeof(int));

	err = bind(listen_sd, (struct sockaddr *)&sa_serv, sizeof(sa_serv));
	SOCKET_ERR(err, "bind");
	err = listen(listen_sd, 1024);
	SOCKET_ERR(err, "listen");

	printf("%s ready. Listening to port '%d'.\n\n", name, PORT);

	client_len = sizeof(sa_cli);
	for (;;) {
		gnutls_init(&session, GNUTLS_SERVER);
		gnutls_priority_set_direct(session,
					   "NORMAL"
					   ":-KX-ALL:+SRP:+SRP-DSS:+SRP-RSA",
					   NULL);
		gnutls_credentials_set(session, GNUTLS_CRD_SRP, srp_cred);
		/* for the certificate authenticated ciphersuites.
		 */
		gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE,
				       cert_cred);

		/* We don't request any certificate from the client.
		 * If we did we would need to verify it. One way of
		 * doing that is shown in the "Verifying a certificate"
		 * example.
		 */
		gnutls_certificate_server_set_request(session,
						      GNUTLS_CERT_IGNORE);

		sd = accept(listen_sd, (struct sockaddr *)&sa_cli, &client_len);

		printf("- connection from %s, port %d\n",
		       inet_ntop(AF_INET, &sa_cli.sin_addr, topbuf,
				 sizeof(topbuf)),
		       ntohs(sa_cli.sin_port));

		gnutls_transport_set_int(session, sd);

		LOOP_CHECK(ret, gnutls_handshake(session));
		if (ret < 0) {
			close(sd);
			gnutls_deinit(session);
			fprintf(stderr, "*** Handshake has failed (%s)\n\n",
				gnutls_strerror(ret));
			continue;
		}
		printf("- Handshake was completed\n");
		printf("- User %s was connected\n",
		       gnutls_srp_server_get_username(session));

		/* print_info(session); */

		for (;;) {
			LOOP_CHECK(ret, gnutls_record_recv(session, buffer,
							   MAX_BUF));

			if (ret == 0) {
				printf("\n- Peer has closed the GnuTLS connection\n");
				break;
			} else if (ret < 0 && gnutls_error_is_fatal(ret) == 0) {
				fprintf(stderr, "*** Warning: %s\n",
					gnutls_strerror(ret));
			} else if (ret < 0) {
				fprintf(stderr,
					"\n*** Received corrupted "
					"data(%d). Closing the connection.\n\n",
					ret);
				break;
			} else if (ret > 0) {
				/* echo data back to the client
				 */
				gnutls_record_send(session, buffer, ret);
			}
		}
		printf("\n");
		/* do not wait for the peer to close the connection. */
		LOOP_CHECK(ret, gnutls_bye(session, GNUTLS_SHUT_WR));

		close(sd);
		gnutls_deinit(session);
	}
	close(listen_sd);

	gnutls_srp_free_server_credentials(srp_cred);
	gnutls_certificate_free_credentials(cert_cred);

	gnutls_global_deinit();

	return 0;
}