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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>
#define KEYFILE "key.pem"
#define CERTFILE "cert.pem"
#define CAFILE "ca.pem"
#define CRLFILE "crl.pem"
/* This is a sample TLS 1.0 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 */
#define DH_BITS 1024
/* These are global */
gnutls_certificate_credentials x509_cred;
gnutls_session initialize_tls_session()
{
gnutls_session session;
gnutls_init(&session, GNUTLS_SERVER);
/* avoid calling all the priority functions, since the defaults
* are adequate.
*/
gnutls_set_default_priority( session);
gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, x509_cred);
/* request client certificate if any.
*/
gnutls_certificate_server_set_request( session, GNUTLS_CERT_REQUEST);
gnutls_dh_set_prime_bits( session, DH_BITS);
return session;
}
static gnutls_dh_params dh_params;
static int generate_dh_params(void) {
/* Generate Diffie Hellman parameters - for use with DHE
* kx algorithms. These should be discarded and regenerated
* once a day, once a week or once a month. Depending on the
* security requirements.
*/
gnutls_dh_params_init( &dh_params);
gnutls_dh_params_generate2( dh_params, DH_BITS);
return 0;
}
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;
/* this must be called once in the program
*/
gnutls_global_init();
gnutls_certificate_allocate_credentials(&x509_cred);
gnutls_certificate_set_x509_trust_file(x509_cred, CAFILE,
GNUTLS_X509_FMT_PEM);
gnutls_certificate_set_x509_crl_file(x509_cred, CRLFILE,
GNUTLS_X509_FMT_PEM);
gnutls_certificate_set_x509_key_file(x509_cred, CERTFILE, KEYFILE,
GNUTLS_X509_FMT_PEM);
generate_dh_params();
gnutls_certificate_set_dh_params( x509_cred, dh_params);
/* 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("Server ready. Listening to port '%d'.\n\n", 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, (gnutls_transport_ptr)sd);
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");
/* see the Getting peer's information example */
/* print_info(session); */
i = 0;
for (;;) {
bzero(buffer, MAX_BUF + 1);
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) {
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,
strlen(buffer));
}
}
printf("\n");
gnutls_bye( session, GNUTLS_SHUT_WR); /* do not wait for
* the peer to close the connection.
*/
close(sd);
gnutls_deinit(session);
}
close(listen_sd);
gnutls_certificate_free_credentials(x509_cred);
gnutls_global_deinit();
return 0;
}
\end{verbatim}
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