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\begin{verbatim}
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <gnutls/gnutls.h>
#include <gnutls/extra.h>
#define SRP_PASSWD "tpasswd"
#define SRP_PASSWD_CONF "tpasswd.conf"
/* This is a sample TLS-SRP echo server.
*/
#define SA struct sockaddr
#define SOCKET_ERR(err,s) if(err==-1) {perror(s);return(1);}
#define MAX_BUF 1024
#define PORT 5556 /* listen to 5556 port */
/* These are global */
gnutls_srp_server_credentials srp_cred;
gnutls_session initialize_tls_session()
{
gnutls_session session;
const int protocol_priority[] = { GNUTLS_TLS1, GNUTLS_SSL3, 0 };
const int kx_priority[] = { GNUTLS_KX_SRP, 0 };
const int cipher_priority[] = { GNUTLS_CIPHER_RIJNDAEL_CBC, GNUTLS_CIPHER_3DES_CBC, 0};
const int comp_priority[] = { GNUTLS_COMP_NULL, 0 };
const int mac_priority[] = { GNUTLS_MAC_SHA, GNUTLS_MAC_MD5, 0 };
gnutls_session_init(&session, GNUTLS_SERVER);
gnutls_protocol_set_priority(session, protocol_priority);
gnutls_cipher_set_priority(session, cipher_priority);
gnutls_compression_set_priority(session, comp_priority);
gnutls_kx_set_priority(session, kx_priority);
gnutls_mac_set_priority(session, mac_priority);
gnutls_credentials_set(session, GNUTLS_CRD_SRP, srp_cred);
/* request client certificate if any.
*/
gnutls_certificate_server_set_request( session, GNUTLS_CERT_IGNORE);
return session;
}
int main()
{
int err, listen_sd, i;
int sd, ret;
struct sockaddr_in sa_serv;
struct sockaddr_in sa_cli;
int client_len;
char topbuf[512];
gnutls_session session;
char buffer[MAX_BUF + 1];
int optval = 1;
char name[256];
strcpy(name, "Echo Server");
/* these must be called once in the program
*/
gnutls_global_init();
gnutls_global_init_extra(); /* for SRP */
/* SRP_PASSWD a password file (created with the included srpcrypt utility)
*/
gnutls_srp_allocate_server_credentials(&srp_cred);
gnutls_srp_set_server_credentials_file(srp_cred, SRP_PASSWD, SRP_PASSWD_CONF);
/* 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, &optval, sizeof(int));
err = bind(listen_sd, (SA *) & 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 (;;) {
session = initialize_tls_session();
sd = accept(listen_sd, (SA *) & 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_ptr( session, sd);
ret = gnutls_handshake( session);
if (ret < 0) {
close(sd);
gnutls_session_deinit(session);
fprintf(stderr, "*** Handshake has failed (%s)\n\n",
gnutls_strerror(ret));
continue;
}
printf("- Handshake was completed\n");
/* print_info(session); */
i = 0;
for (;;) {
bzero(buffer, MAX_BUF + 1);
ret = gnutls_record_recv( session, buffer, MAX_BUF);
if (gnutls_error_is_fatal(ret) == 1 || ret == 0) {
if (ret == 0) {
printf
("\n- Peer has closed the GNUTLS connection\n");
break;
} else {
fprintf(stderr,
"\n*** Received corrupted data(%d). Closing the connection.\n\n",
ret);
break;
}
}
if (ret > 0) {
/* echo data back to the client
*/
gnutls_record_send( session, buffer,
strlen(buffer));
}
if (ret == GNUTLS_E_WARNING_ALERT_RECEIVED || ret == GNUTLS_E_FATAL_ALERT_RECEIVED) {
ret = gnutls_alert_get(session);
printf("* Received alert '%d' - '%s'.\n", ret, gnutls_alert_get_name( ret));
}
}
printf("\n");
gnutls_bye( session, GNUTLS_SHUT_WR); /* do not wait for
* the peer to close the connection.
*/
close(sd);
gnutls_session_deinit(session);
}
close(listen_sd);
gnutls_srp_free_server_credentials(srp_cred);
gnutls_global_deinit();
return 0;
}
\end{verbatim}
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