/* Very simple TLS client, to test TLS 1.3 connections */
#define MAXHOSTNAME 256
#define MAXPORTNAME 128
#define MAXMSG 1024
/* Default port */
#define PORT "https"
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <errno.h>
#include <gnutls/gnutls.h>
/* https://gnutls.org/manual/gnutls.html */
int
main(argc, argv)
 int argc;
 char **argv;
{
 gnutls_session_t *session = malloc(sizeof(gnutls_session_t));
 int tls_result;
 int last_alert;
 int cert_status;
 gnutls_datum_t *cert_out;
 int cert_type;
 int result;
 char *hostname = malloc(MAXHOSTNAME);
 char *portname = malloc(MAXPORTNAME);
 int sockfd;
 struct addrinfo hints, *res;
 gnutls_certificate_credentials_t xcred;
 if (argc <= 1 &#124;&#124; argc>= 4) {
 fprintf(stderr, "Usage: %s server-name [server-port]\n", argv[0]);
 exit(1);
 }
 strcpy(hostname, argv[1]);
 if (argc == 3) {
 strcpy(portname, argv[2]);
 } else {
 strcpy(portname, PORT);
 }
 tls_result = gnutls_certificate_allocate_credentials(&xcred);
 if (tls_result != GNUTLS_E_SUCCESS) {
 fprintf(stderr, "Cannot allocate credentials: %s\n",
 gnutls_strerror(tls_result));
 exit(1);
 }
 tls_result = gnutls_certificate_set_x509_system_trust(xcred);
 if (tls_result < 0) { fprintf(stderr, "Cannot load credentials: %s\n", gnutls_strerror(tls_result)); exit(1); } tls_result = gnutls_init(session, GNUTLS_CLIENT); if (tls_result != GNUTLS_E_SUCCESS) { fprintf(stderr, "Cannot create a new TLS session: %s\n", gnutls_strerror(tls_result)); exit(1); } tls_result = gnutls_credentials_set(*session, GNUTLS_CRD_CERTIFICATE, xcred); /* Mandatory * or * "no * cipher * suites * found" */ if (tls_result != GNUTLS_E_SUCCESS) { fprintf(stderr, "Cannot set credentials: %s\n", gnutls_strerror(tls_result)); exit(1); } tls_result = gnutls_priority_set_direct(*session, "NORMAL:-VERS-ALL:+VERS-TLS1.3:+VERS-TLS1.2:+VERS-TLS1.1:+VERS-TLS1.0", NULL); if (tls_result != GNUTLS_E_SUCCESS) { fprintf(stderr, "Cannot set priorities: %s\n", gnutls_strerror(tls_result)); exit(1); } gnutls_session_set_verify_cert(*session, hostname, 0); tls_result = gnutls_server_name_set(*session, GNUTLS_NAME_DNS, hostname, strlen(hostname)); if (tls_result != GNUTLS_E_SUCCESS) { fprintf(stderr, "Cannot set Server Name Indication: %s\n", gnutls_strerror(tls_result)); exit(1); } memset(&hints, 0, sizeof(hints)); hints.ai_family = PF_UNSPEC; /* v4 or v6, I don't care */ hints.ai_socktype = SOCK_STREAM; result = getaddrinfo(hostname, portname, &hints, &res); if (result != 0) { fprintf(stderr, "Cannot resolve name '%s : %s' (wrong name or wrong port): %d\n", hostname, portname, result); exit(1); } sockfd = socket(res->ai_family, res->ai_socktype, 0);
 if (sockfd == -1) {
 fprintf(stderr, "Cannot create socket\n");
 exit(1);
 }
 result = connect(sockfd, res->ai_addr, res->ai_addrlen);
 if (result != 0) {
 fprintf(stderr, "Cannot connect to %s: %d\n", hostname, errno);
 exit(1);
 }
 gnutls_transport_set_int(*session, sockfd);
 tls_result = gnutls_handshake(*session);
 if (tls_result != GNUTLS_E_SUCCESS) {
 fprintf(stderr, "Cannot start the TLS session to %s: ", hostname);
 if (tls_result == GNUTLS_E_FATAL_ALERT_RECEIVED) {
 last_alert = gnutls_alert_get(*session);
 fprintf(stderr, "Received alert '%d': %s.\n", last_alert,
 gnutls_alert_get_name(last_alert));
 } else if (tls_result == GNUTLS_E_CERTIFICATE_VERIFICATION_ERROR) {
 cert_status = gnutls_session_get_verify_cert_status(*session);
 cert_out = malloc(sizeof(gnutls_datum_t));
 cert_out->size = 0;
 cert_out->data = malloc(MAXMSG);
 cert_out->data[0] = '0円';
 cert_type = gnutls_certificate_type_get(*session);
 tls_result =
 gnutls_certificate_verification_status_print(cert_status, cert_type,
 cert_out, 0);
 if (tls_result != GNUTLS_E_SUCCESS) {
 fprintf(stderr, "Error in printing the certificate check status\n");
 exit(1);
 }
 fprintf(stderr, "%s\n", cert_out->data);
 } else {
 fprintf(stderr, "%s\n", gnutls_strerror(tls_result));
 }
 exit(1);
 }
 fprintf
 (stderr, "TLS connection using \"%s %s\"\n",
 gnutls_protocol_get_name(gnutls_protocol_get_version(*session)),
 gnutls_cipher_get_name(gnutls_cipher_get(*session)));
}
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