GNUTLS: Avoid null dereference in constructing ciphersuite

[solanum.git] / librb / src / gnutls.c

/*
 *  librb: a library used by charybdis and other things
 *  gnutls.c: gnutls related code
 *
 *  Copyright (C) 2007-2008 ircd-ratbox development team
 *  Copyright (C) 2007-2008 Aaron Sethman <androsyn@ratbox.org>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301
 *  USA
 *
 */

#include <librb_config.h>
#include <rb_lib.h>
#include <commio-int.h>
#include <commio-ssl.h>
#include <stdbool.h>
#ifdef HAVE_GNUTLS

#include <gnutls/gnutls.h>
#include <gnutls/x509.h>
#include <gnutls/abstract.h>

#if (GNUTLS_VERSION_MAJOR < 3)
# include <gcrypt.h>
#else
# include <gnutls/crypto.h>
#endif

static gnutls_certificate_credentials_t x509;
static gnutls_dh_params_t dh_params;
static gnutls_priority_t default_priority;

/* These are all used for getting GnuTLS to supply a client cert. */
#define MAX_CERTS 6
static unsigned int x509_cert_count;
static gnutls_x509_crt_t x509_cert[MAX_CERTS];
static gnutls_x509_privkey_t x509_key;
#if GNUTLS_VERSION_MAJOR < 3
static int cert_callback(gnutls_session_t session, const gnutls_datum_t *req_ca_rdn, int nreqs,
        const gnutls_pk_algorithm_t *sign_algos, int sign_algos_len, gnutls_retr_st *st);
#else
static int cert_callback(gnutls_session_t session, const gnutls_datum_t *req_ca_rdn, int nreqs,
        const gnutls_pk_algorithm_t *sign_algos, int sign_algos_len, gnutls_retr2_st *st);
#endif

#define SSL_P(x) *((gnutls_session_t *)F->ssl)

void
rb_ssl_shutdown(rb_fde_t *F)
{
        int i;
        if(F == NULL || F->ssl == NULL)
                return;
        for(i = 0; i < 4; i++)
        {
                if(gnutls_bye(SSL_P(F), GNUTLS_SHUT_RDWR) == GNUTLS_E_SUCCESS)
                        break;
        }
        gnutls_deinit(SSL_P(F));
        rb_free(F->ssl);
}

unsigned int
rb_ssl_handshake_count(rb_fde_t *F)
{
        return F->handshake_count;
}

void
rb_ssl_clear_handshake_count(rb_fde_t *F)
{
        F->handshake_count = 0;
}

static void
rb_ssl_timeout(rb_fde_t *F, void *notused)
{
        lrb_assert(F->accept != NULL);
        F->accept->callback(F, RB_ERR_TIMEOUT, NULL, 0, F->accept->data);
}


static int
do_ssl_handshake(rb_fde_t *F, PF * callback, void *data)
{
        int ret;
        int flags;

        ret = gnutls_handshake(SSL_P(F));
        if(ret < 0)
        {
                if((ret == GNUTLS_E_INTERRUPTED && rb_ignore_errno(errno)) || ret == GNUTLS_E_AGAIN)
                {
                        if(gnutls_record_get_direction(SSL_P(F)) == 0)
                                flags = RB_SELECT_READ;
                        else
                                flags = RB_SELECT_WRITE;
                        rb_setselect(F, flags, callback, data);
                        return 0;
                }
                F->ssl_errno = ret;
                return -1;
        }
        return 1;               /* handshake is finished..go about life */
}

static void
rb_ssl_tryaccept(rb_fde_t *F, void *data)
{
        int ret;
        struct acceptdata *ad;

        lrb_assert(F->accept != NULL);

        ret = do_ssl_handshake(F, rb_ssl_tryaccept, NULL);

        /* do_ssl_handshake does the rb_setselect */
        if(ret == 0)
                return;

        ad = F->accept;
        F->accept = NULL;
        rb_settimeout(F, 0, NULL, NULL);
        rb_setselect(F, RB_SELECT_READ | RB_SELECT_WRITE, NULL, NULL);

        if(ret > 0)
                ad->callback(F, RB_OK, (struct sockaddr *)&ad->S, ad->addrlen, ad->data);
        else
                ad->callback(F, RB_ERROR_SSL, NULL, 0, ad->data);

        rb_free(ad);
}

void
rb_ssl_start_accepted(rb_fde_t *new_F, ACCB * cb, void *data, int timeout)
{
        gnutls_session_t *ssl;
        new_F->type |= RB_FD_SSL;
        ssl = new_F->ssl = rb_malloc(sizeof(gnutls_session_t));
        new_F->accept = rb_malloc(sizeof(struct acceptdata));

        new_F->accept->callback = cb;
        new_F->accept->data = data;
        rb_settimeout(new_F, timeout, rb_ssl_timeout, NULL);

        new_F->accept->addrlen = 0;

        gnutls_init(ssl, GNUTLS_SERVER);
        gnutls_set_default_priority(*ssl);
        gnutls_credentials_set(*ssl, GNUTLS_CRD_CERTIFICATE, x509);
        gnutls_dh_set_prime_bits(*ssl, 1024);
        gnutls_transport_set_ptr(*ssl, (gnutls_transport_ptr_t) (long int)new_F->fd);
        gnutls_certificate_server_set_request(*ssl, GNUTLS_CERT_REQUEST);
        gnutls_priority_set(*ssl, default_priority);

        if(do_ssl_handshake(new_F, rb_ssl_tryaccept, NULL))
        {
                struct acceptdata *ad = new_F->accept;
                new_F->accept = NULL;
                ad->callback(new_F, RB_OK, (struct sockaddr *)&ad->S, ad->addrlen, ad->data);
                rb_free(ad);
        }

}




void
rb_ssl_accept_setup(rb_fde_t *F, rb_fde_t *new_F, struct sockaddr *st, int addrlen)
{
        new_F->type |= RB_FD_SSL;
        new_F->ssl = rb_malloc(sizeof(gnutls_session_t));
        new_F->accept = rb_malloc(sizeof(struct acceptdata));

        new_F->accept->callback = F->accept->callback;
        new_F->accept->data = F->accept->data;
        rb_settimeout(new_F, 10, rb_ssl_timeout, NULL);
        memcpy(&new_F->accept->S, st, addrlen);
        new_F->accept->addrlen = addrlen;

        gnutls_init((gnutls_session_t *) new_F->ssl, GNUTLS_SERVER);
        gnutls_set_default_priority(SSL_P(new_F));
        gnutls_credentials_set(SSL_P(new_F), GNUTLS_CRD_CERTIFICATE, x509);
        gnutls_dh_set_prime_bits(SSL_P(new_F), 1024);
        gnutls_transport_set_ptr(SSL_P(new_F), (gnutls_transport_ptr_t) (long int)rb_get_fd(new_F));
        gnutls_certificate_server_set_request(SSL_P(new_F), GNUTLS_CERT_REQUEST);
        gnutls_priority_set(SSL_P(F), default_priority);

        if(do_ssl_handshake(F, rb_ssl_tryaccept, NULL))
        {
                struct acceptdata *ad = F->accept;
                F->accept = NULL;
                ad->callback(F, RB_OK, (struct sockaddr *)&ad->S, ad->addrlen, ad->data);
                rb_free(ad);
        }
}




static ssize_t
rb_ssl_read_or_write(int r_or_w, rb_fde_t *F, void *rbuf, const void *wbuf, size_t count)
{
        ssize_t ret;
        gnutls_session_t *ssl = F->ssl;

        if(r_or_w == 0)
                ret = gnutls_record_recv(*ssl, rbuf, count);
        else
                ret = gnutls_record_send(*ssl, wbuf, count);

        if(ret < 0)
        {
                switch (ret)
                {
                case GNUTLS_E_AGAIN:
                case GNUTLS_E_INTERRUPTED:
                        if(rb_ignore_errno(errno))
                        {
                                if(gnutls_record_get_direction(*ssl) == 0)
                                        return RB_RW_SSL_NEED_READ;
                                else
                                        return RB_RW_SSL_NEED_WRITE;
                                break;
                        }
                default:
                        F->ssl_errno = ret;
                        errno = EIO;
                        return RB_RW_IO_ERROR;
                }
        }
        return ret;
}

ssize_t
rb_ssl_read(rb_fde_t *F, void *buf, size_t count)
{
        return rb_ssl_read_or_write(0, F, buf, NULL, count);
}

ssize_t
rb_ssl_write(rb_fde_t *F, const void *buf, size_t count)
{
        return rb_ssl_read_or_write(1, F, NULL, buf, count);
}

#if (GNUTLS_VERSION_MAJOR < 3)
static void
rb_gcry_random_seed(void *unused)
{
        gcry_fast_random_poll();
}
#endif

int
rb_init_ssl(void)
{
        gnutls_global_init();

        if(gnutls_certificate_allocate_credentials(&x509) != GNUTLS_E_SUCCESS)
        {
                rb_lib_log("rb_init_ssl: Unable to allocate SSL/TLS certificate credentials");
                return 0;
        }

#if GNUTLS_VERSION_MAJOR < 3
        gnutls_certificate_client_set_retrieve_function(x509, cert_callback);
#else
        gnutls_certificate_set_retrieve_function(x509, cert_callback);
#endif

#if (GNUTLS_VERSION_MAJOR < 3)
        rb_event_addish("rb_gcry_random_seed", rb_gcry_random_seed, NULL, 300);
#endif

        return 1;
}

/* We only have one certificate to authenticate with, as both client and server.  Unfortunately,
 * GnuTLS tries to be clever, and as client, will attempt to use a certificate that the server
 * will trust.  We usually use self-signed certs, though, so the result of this search is always
 * nothing.  Therefore, it uses no certificate to authenticate as a client.  This is undesirable
 * as it breaks fingerprint auth.  Thus, we use this callback to force GnuTLS to always
 * authenticate with our certificate at all times.
 */
#if GNUTLS_VERSION_MAJOR < 3
static int
cert_callback(gnutls_session_t session, const gnutls_datum_t *req_ca_rdn, int nreqs,
        const gnutls_pk_algorithm_t *sign_algos, int sign_algos_len, gnutls_retr_st *st)
#else
static int
cert_callback(gnutls_session_t session, const gnutls_datum_t *req_ca_rdn, int nreqs,
        const gnutls_pk_algorithm_t *sign_algos, int sign_algos_len, gnutls_retr2_st *st)
#endif
{
        /* XXX - ugly hack. Tell GnuTLS to use the first (only) certificate we have for auth. */
#if (GNUTLS_VERSION_MAJOR < 3)
        st->type = GNUTLS_CRT_X509;
#else
        st->cert_type = GNUTLS_CRT_X509;
        st->key_type = GNUTLS_PRIVKEY_X509;
#endif
        st->ncerts = x509_cert_count;
        st->cert.x509 = x509_cert;
        st->key.x509 = x509_key;
        st->deinit_all = 0;

        return 0;
}

static void
rb_free_datum_t(gnutls_datum_t * d)
{
        rb_free(d->data);
        rb_free(d);
}

static gnutls_datum_t *
rb_load_file_into_datum_t(const char *file)
{
        FILE *f;
        gnutls_datum_t *datum;
        struct stat fileinfo;
        int count;
        if((f = fopen(file, "r")) == NULL)
                return NULL;
        if(fstat(fileno(f), &fileinfo))
                return NULL;

        datum = rb_malloc(sizeof(gnutls_datum_t));

        if(fileinfo.st_size > 131072)   /* deal with retards */
                datum->size = 131072;
        else
                datum->size = fileinfo.st_size;

        datum->data = rb_malloc(datum->size + 1);
        count = fread(datum->data, datum->size, 1, f);
        fclose(f);

        if(count != 1)
        {
                rb_free_datum_t(datum);
                return NULL;
        }
        return datum;
}

int
rb_setup_ssl_server(const char *certfile, const char *keyfile, const char *dhfile, const char *cipher_list)
{
        int ret;
        const char *err;
        gnutls_datum_t *d_cert, *d_key;

        if(certfile == NULL)
        {
                rb_lib_log("rb_setup_ssl_server: No certificate file");
                return 0;
        }

        if(keyfile == NULL)
                keyfile = certfile;

        if((d_cert = rb_load_file_into_datum_t(certfile)) == NULL)
        {
                rb_lib_log("rb_setup_ssl_server: Error loading certificate: %s", strerror(errno));
                return 0;
        }

        if((d_key = rb_load_file_into_datum_t(keyfile)) == NULL)
        {
                rb_lib_log("rb_setup_ssl_server: Error loading key: %s", strerror(errno));
                return 0;
        }

        /* In addition to creating the certificate set, we also need to store our cert elsewhere
         * so we can force GnuTLS to identify with it when acting as a client.
         */
        gnutls_x509_privkey_init(&x509_key);
        if ((ret = gnutls_x509_privkey_import(x509_key, d_key, GNUTLS_X509_FMT_PEM)) != GNUTLS_E_SUCCESS)
        {
                rb_lib_log("rb_setup_ssl_server: Error loading key file: %s", gnutls_strerror(ret));
                return 0;
        }

        x509_cert_count = MAX_CERTS;
        if ((ret = gnutls_x509_crt_list_import(x509_cert, &x509_cert_count, d_cert, GNUTLS_X509_FMT_PEM,
                GNUTLS_X509_CRT_LIST_IMPORT_FAIL_IF_EXCEED)) < 0)
        {
                rb_lib_log("rb_setup_ssl_server: Error loading certificate: %s", gnutls_strerror(ret));
                return 0;
        }
        x509_cert_count = ret;

        if((ret =
            gnutls_certificate_set_x509_key_mem(x509, d_cert, d_key,
                                                GNUTLS_X509_FMT_PEM)) != GNUTLS_E_SUCCESS)
        {
                rb_lib_log("rb_setup_ssl_server: Error loading certificate or key file: %s",
                           gnutls_strerror(ret));
                return 0;
        }

        rb_free_datum_t(d_cert);
        rb_free_datum_t(d_key);

        if(dhfile != NULL)
        {
                if(gnutls_dh_params_init(&dh_params) == GNUTLS_E_SUCCESS)
                {
                        gnutls_datum_t *data;
                        int xret;
                        data = rb_load_file_into_datum_t(dhfile);
                        if(data != NULL)
                        {
                                xret = gnutls_dh_params_import_pkcs3(dh_params, data,
                                                                     GNUTLS_X509_FMT_PEM);
                                if(xret < 0)
                                        rb_lib_log
                                                ("rb_setup_ssl_server: Error parsing DH file: %s\n",
                                                 gnutls_strerror(xret));
                                rb_free_datum_t(data);
                        }
                        gnutls_certificate_set_dh_params(x509, dh_params);
                }
                else
                        rb_lib_log("rb_setup_ssl_server: Unable to setup DH parameters");
        }

        ret = gnutls_priority_init(&default_priority, cipher_list, &err);
        if (ret < 0)
        {
                rb_lib_log("rb_setup_ssl_server: syntax error (using defaults instead) in ssl cipher list at: %s", err);
                gnutls_priority_init(&default_priority, NULL, &err);
                return 1;
        }

        return 1;
}

int
rb_ssl_listen(rb_fde_t *F, int backlog, int defer_accept)
{
        int result;

        result = rb_listen(F, backlog, defer_accept);
        F->type = RB_FD_SOCKET | RB_FD_LISTEN | RB_FD_SSL;

        return result;
}

struct ssl_connect
{
        CNCB *callback;
        void *data;
        int timeout;
};

static void
rb_ssl_connect_realcb(rb_fde_t *F, int status, struct ssl_connect *sconn)
{
        F->connect->callback = sconn->callback;
        F->connect->data = sconn->data;
        rb_free(sconn);
        rb_connect_callback(F, status);
}

static void
rb_ssl_tryconn_timeout_cb(rb_fde_t *F, void *data)
{
        rb_ssl_connect_realcb(F, RB_ERR_TIMEOUT, data);
}

static void
rb_ssl_tryconn_cb(rb_fde_t *F, void *data)
{
        struct ssl_connect *sconn = data;
        int ret;

        ret = do_ssl_handshake(F, rb_ssl_tryconn_cb, (void *)sconn);

        switch (ret)
        {
        case -1:
                rb_ssl_connect_realcb(F, RB_ERROR_SSL, sconn);
                break;
        case 0:
                /* do_ssl_handshake does the rb_setselect stuff */
                return;
        default:
                break;


        }
        rb_ssl_connect_realcb(F, RB_OK, sconn);
}

static void
rb_ssl_tryconn(rb_fde_t *F, int status, void *data)
{
        struct ssl_connect *sconn = data;
        if(status != RB_OK)
        {
                rb_ssl_connect_realcb(F, status, sconn);
                return;
        }

        F->type |= RB_FD_SSL;


        rb_settimeout(F, sconn->timeout, rb_ssl_tryconn_timeout_cb, sconn);
        F->ssl = rb_malloc(sizeof(gnutls_session_t));
        gnutls_init(F->ssl, GNUTLS_CLIENT);
        gnutls_set_default_priority(SSL_P(F));
        gnutls_credentials_set(SSL_P(F), GNUTLS_CRD_CERTIFICATE, x509);
        gnutls_dh_set_prime_bits(SSL_P(F), 1024);
        gnutls_transport_set_ptr(SSL_P(F), (gnutls_transport_ptr_t) (long int)F->fd);
        gnutls_priority_set(SSL_P(F), default_priority);

        do_ssl_handshake(F, rb_ssl_tryconn_cb, (void *)sconn);
}

void
rb_connect_tcp_ssl(rb_fde_t *F, struct sockaddr *dest,
                   struct sockaddr *clocal, CNCB * callback, void *data, int timeout)
{
        struct ssl_connect *sconn;
        if(F == NULL)
                return;

        sconn = rb_malloc(sizeof(struct ssl_connect));
        sconn->data = data;
        sconn->callback = callback;
        sconn->timeout = timeout;
        rb_connect_tcp(F, dest, clocal, rb_ssl_tryconn, sconn, timeout);

}

void
rb_ssl_start_connected(rb_fde_t *F, CNCB * callback, void *data, int timeout)
{
        struct ssl_connect *sconn;
        if(F == NULL)
                return;

        sconn = rb_malloc(sizeof(struct ssl_connect));
        sconn->data = data;
        sconn->callback = callback;
        sconn->timeout = timeout;
        F->connect = rb_malloc(sizeof(struct conndata));
        F->connect->callback = callback;
        F->connect->data = data;
        F->type |= RB_FD_SSL;
        F->ssl = rb_malloc(sizeof(gnutls_session_t));

        gnutls_init(F->ssl, GNUTLS_CLIENT);
        gnutls_set_default_priority(SSL_P(F));
        gnutls_credentials_set(SSL_P(F), GNUTLS_CRD_CERTIFICATE, x509);
        gnutls_dh_set_prime_bits(SSL_P(F), 1024);
        gnutls_transport_set_ptr(SSL_P(F), (gnutls_transport_ptr_t) (long int)F->fd);
        gnutls_priority_set(SSL_P(F), default_priority);

        rb_settimeout(F, sconn->timeout, rb_ssl_tryconn_timeout_cb, sconn);

        do_ssl_handshake(F, rb_ssl_tryconn_cb, (void *)sconn);
}

int
rb_init_prng(const char *path, prng_seed_t seed_type)
{
#if GNUTLS_VERSION_MAJOR < 3
        gcry_fast_random_poll();
#endif
        return 1;
}

int
rb_get_random(void *buf, size_t length)
{
#if GNUTLS_VERSION_MAJOR < 3
        gcry_randomize(buf, length, GCRY_STRONG_RANDOM);
#else
        gnutls_rnd(GNUTLS_RND_KEY, buf, length);
#endif
        return 1;
}

const char *
rb_get_ssl_strerror(rb_fde_t *F)
{
        return gnutls_strerror(F->ssl_errno);
}

static int
make_certfp(gnutls_x509_crt_t cert, uint8_t certfp[RB_SSL_CERTFP_LEN], int method)
{
        gnutls_digest_algorithm_t algo;
        size_t digest_size;
        bool spki = false;
        int len;

        switch(method)
        {
        case RB_SSL_CERTFP_METH_CERT_SHA1:
                algo = GNUTLS_DIG_SHA1;
                len = RB_SSL_CERTFP_LEN_SHA1;
                break;
        case RB_SSL_CERTFP_METH_SPKI_SHA256:
                spki = true;
        case RB_SSL_CERTFP_METH_CERT_SHA256:
                algo = GNUTLS_DIG_SHA256;
                len = RB_SSL_CERTFP_LEN_SHA256;
                break;
        case RB_SSL_CERTFP_METH_SPKI_SHA512:
                spki = true;
        case RB_SSL_CERTFP_METH_CERT_SHA512:
                algo = GNUTLS_DIG_SHA512;
                len = RB_SSL_CERTFP_LEN_SHA512;
                break;
        default:
                return 0;
        }

        if (!spki)
        {
                if (gnutls_x509_crt_get_fingerprint(cert, algo, certfp, &digest_size) != 0)
                        len = 0;
        }
        else
        {
                gnutls_pubkey_t pubkey;
                unsigned char *der_pubkey = NULL;
                size_t der_pubkey_len = 0;

                if (gnutls_pubkey_init(&pubkey) == GNUTLS_E_SUCCESS)
                {
                        if (gnutls_pubkey_import_x509(pubkey, cert, 0) == GNUTLS_E_SUCCESS)
                        {
                                if (gnutls_pubkey_export(pubkey, GNUTLS_X509_FMT_DER, der_pubkey, &der_pubkey_len) == GNUTLS_E_SHORT_MEMORY_BUFFER)
                                {
                                        der_pubkey = rb_malloc(der_pubkey_len);

                                        if (gnutls_pubkey_export(pubkey, GNUTLS_X509_FMT_DER, der_pubkey, &der_pubkey_len) != GNUTLS_E_SUCCESS)
                                        {
                                                rb_free(der_pubkey);
                                                der_pubkey = NULL;
                                        }
                                }
                        }

                        gnutls_pubkey_deinit(pubkey);
                }

                if (der_pubkey)
                {
                        if (gnutls_hash_fast(algo, der_pubkey, der_pubkey_len, certfp) != 0)
                                len = 0;

                        rb_free(der_pubkey);
                }
                else
                {
                        len = 0;
                }
        }

        return len;
}

int
rb_get_ssl_certfp(rb_fde_t *F, uint8_t certfp[RB_SSL_CERTFP_LEN], int method)
{
        gnutls_x509_crt_t cert;
        unsigned int cert_list_size;
        const gnutls_datum_t *cert_list;
        int len;

        if (gnutls_certificate_type_get(SSL_P(F)) != GNUTLS_CRT_X509)
                return 0;

        if (gnutls_x509_crt_init(&cert) < 0)
                return 0;

        cert_list_size = 0;
        cert_list = gnutls_certificate_get_peers(SSL_P(F), &cert_list_size);
        if (cert_list == NULL)
        {
                gnutls_x509_crt_deinit(cert);
                return 0;
        }

        if (gnutls_x509_crt_import(cert, &cert_list[0], GNUTLS_X509_FMT_DER) < 0)
        {
                gnutls_x509_crt_deinit(cert);
                return 0;
        }

        len = make_certfp(cert, certfp, method);
        gnutls_x509_crt_deinit(cert);
        return len;
}

int
rb_get_ssl_certfp_file(const char *filename, uint8_t certfp[RB_SSL_CERTFP_LEN], int method)
{
        gnutls_x509_crt_t cert;
        gnutls_datum_t *d_cert;
        unsigned int len;

        if ((d_cert = rb_load_file_into_datum_t(filename)) == NULL)
                return -1;

        if (gnutls_x509_crt_init(&cert) < 0)
                return -1;

        if (gnutls_x509_crt_import(cert, d_cert, GNUTLS_X509_FMT_PEM) != 0)
                return -1;

        len = make_certfp(cert, certfp, method);
        gnutls_x509_crt_deinit(cert);
        return len;
}

int
rb_supports_ssl(void)
{
        return 1;
}

void
rb_get_ssl_info(char *buf, size_t len)
{
        snprintf(buf, len, "GNUTLS: compiled (%s), library (%s)",
                    LIBGNUTLS_VERSION, gnutls_check_version(NULL));
}

const char *
rb_ssl_get_cipher(rb_fde_t *F)
{
        static char buf[1024];

        const char* proto_name =
            gnutls_protocol_get_name(gnutls_protocol_get_version(SSL_P(F)));

        const char* kex_alg_name =
            gnutls_kx_get_name(gnutls_kx_get(SSL_P(F)));

        const char* cipher_alg_name =
            gnutls_cipher_get_name(gnutls_cipher_get(SSL_P(F)));

        const char* mac_alg_name =
            gnutls_mac_get_name(gnutls_mac_get(SSL_P(F)));

        (void) snprintf(buf, sizeof buf, "%s%s%s%s%s%s%s",
                        proto_name ? proto_name : "",
                        proto_name ? ", " : "",
                        kex_alg_name ? kex_alg_name : "",
                        kex_alg_name ? "-" : "",
                        cipher_alg_name ? cipher_alg_name : "",
                        cipher_alg_name ? "-" : "",
                        mac_alg_name ? mac_alg_name : "");

        return buf;
}

#endif /* HAVE_GNUTLS */