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\begin{verbatim}
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <gnutls.h>
#define MAX_BUF 1024
#define CRLFILE "crl.pem"
#define CAFILE "ca.pem"
#define SA struct sockaddr
#define MSG "GET / HTTP/1.0\r\n\r\n"
int main()
{
const char *PORT = "443";
const char *SERVER = "127.0.0.1";
int err, ret;
int sd, ii;
struct sockaddr_in sa;
GNUTLS_STATE state;
char buffer[MAX_BUF + 1];
X509PKI_CLIENT_CREDENTIALS xcred;
const int protocol_priority[] = { GNUTLS_TLS1, GNUTLS_SSL3, 0 };
const int kx_priority[] = { GNUTLS_KX_X509PKI_RSA, 0 };
const int cipher_priority[] = { GNUTLS_CIPHER_3DES_CBC, GNUTLS_CIPHER_ARCFOUR, 0};
const int comp_priority[] = { GNUTLS_COMP_ZLIB, GNUTLS_COMP_NULL, 0 };
const int mac_priority[] = { GNUTLS_MAC_SHA, GNUTLS_MAC_MD5, 0 };
if (gnutls_global_init() < 0) {
fprintf(stderr, "global state initialization error\n");
exit(1);
}
/* X509 stuff */
if (gnutls_x509pki_allocate_client_sc(&xcred, 0) < 0) { /* no client private key */
fprintf(stderr, "memory error\n");
exit(1);
}
/* set's the trusted cas file
*/
gnutls_x509pki_set_client_trust_file(xcred, CAFILE, CRLFILE);
/* connects to server
*/
sd = socket(AF_INET, SOCK_STREAM, 0);
memset(&sa, '\0', sizeof(sa));
sa.sin_family = AF_INET;
sa.sin_port = htons(atoi(PORT));
inet_pton(AF_INET, SERVER, &sa.sin_addr);
err = connect(sd, (SA *) & sa, sizeof(sa));
if (err < 0) {
fprintf(stderr, "Connect error\n");
exit(1);
}
/* Initialize TLS state
*/
gnutls_init(&state, GNUTLS_CLIENT);
/* allow both SSL3 and TLS1
*/
gnutls_protocol_set_priority(state, protocol_priority);
/* allow only ARCFOUR and 3DES ciphers
* (3DES has the highest priority)
*/
gnutls_cipher_set_priority(state, cipher_priority);
/* only allow null compression
*/
gnutls_compression_set_priority(state, comp_priority);
/* use GNUTLS_KX_X509PKI_RSA
*/
gnutls_kx_set_priority(state, kx_priority);
/* allow the usage of both SHA and MD5
*/
gnutls_mac_set_priority(state, mac_priority);
/* put the x509 credentials to the current state
*/
gnutls_set_cred(state, GNUTLS_X509PKI, xcred);
gnutls_transport_set_ptr( state, sd);
/* Perform the TLS handshake
*/
ret = gnutls_handshake( state);
if (ret < 0) {
fprintf(stderr, "*** Handshake failed\n");
gnutls_perror(ret);
goto end;
} else {
printf("- Handshake was completed\n");
}
gnutls_write( state, MSG, strlen(MSG));
ret = gnutls_read( state, buffer, MAX_BUF);
if (gnutls_is_fatal_error(ret) == 1 || ret == 0) {
if (ret == 0) {
printf("- Peer has closed the GNUTLS connection\n");
goto end;
} else {
fprintf(stderr, "*** Received corrupted data(%d) - server has terminated the connection abnormally\n",
ret);
goto end;
}
} else {
if (ret == GNUTLS_E_WARNING_ALERT_RECEIVED || ret == GNUTLS_E_FATAL_ALERT_RECEIVED)
printf("* Received alert [%d]\n", gnutls_get_last_alert(state));
if (ret == GNUTLS_E_REHANDSHAKE)
printf("* Received HelloRequest message (server asked to rehandshake)\n");
gnutls_send_appropriate_alert( state, ret); /* we don't want rehandshake */
}
if (ret > 0) {
printf("- Received %d bytes: ", ret);
for (ii = 0; ii < ret; ii++) {
fputc(buffer[ii], stdout);
}
fputs("\n", stdout);
}
gnutls_bye( state, GNUTLS_SHUT_RDWR);
end:
shutdown(sd, SHUT_RDWR); /* no more receptions */
close(sd);
gnutls_deinit(state);
gnutls_x509pki_free_client_sc(xcred);
gnutls_global_deinit();
return 0;
}
\end{verbatim}
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