diff --git a/_gnutls.h b/_gnutls.h
index bc5048b..9bccd2f 100644
--- a/_gnutls.h
+++ b/_gnutls.h
@@ -55,4 +55,7 @@ int get_cert_dn(gnutls_pcert_st *st, int index, char *out);
 void free_cert_list(gnutls_pcert_st *st, int size);
 gnutls_pcert_st *get_peer_certificate(gnutls_session_t sess, int *pcert_length);
 int cert_check_hostname(gnutls_pcert_st *st, int len, char *hostname);
+
+void init_priority_cache();
+void init_xcred();
 #endif
\ No newline at end of file
diff --git a/gnutls.c b/gnutls.c
index 412b830..e0082ad 100644
--- a/gnutls.c
+++ b/gnutls.c
@@ -6,6 +6,8 @@ gnutls_datum_t out;
 int status;
 int type;
 
+static gnutls_certificate_credentials_t xcred;
+static gnutls_priority_t priority_cache;
 int _init_session(struct session *);
 int cert_select_callback(gnutls_session_t sess, const gnutls_datum_t *req_ca_dn,
 						 int nreqs, const gnutls_pk_algorithm_t *pk_algos,
@@ -36,13 +38,33 @@ struct session *init_gnutls_server_session()
 	return sess;
 }
 
+void init_priority_cache()
+{
+	if (priority_cache == NULL)
+	{
+		//printf("init priority cache\n");
+		gnutls_priority_init(&priority_cache, NULL, NULL);
+	}
+}
+
+void init_xcred()
+{
+	if (xcred == NULL)
+	{
+		//printf("init xcred\n");
+		gnutls_certificate_allocate_credentials(&xcred);
+		gnutls_certificate_set_x509_system_trust(xcred);
+		gnutls_certificate_set_retrieve_function2(xcred, cert_select_callback);
+	}
+}
+
 int _init_session(struct session *sess)
 {
-	gnutls_certificate_allocate_credentials(&sess->xcred);
-	gnutls_certificate_set_x509_system_trust(sess->xcred);
-	gnutls_certificate_set_retrieve_function2(sess->xcred, cert_select_callback);
-	gnutls_set_default_priority(sess->session);
-	gnutls_credentials_set(sess->session, GNUTLS_CRD_CERTIFICATE, sess->xcred);
+	//init_xcred();
+	//init_priority_cache();
+	//gnutls_set_default_priority(sess->session);
+	gnutls_priority_set(sess->session, priority_cache);
+	gnutls_credentials_set(sess->session, GNUTLS_CRD_CERTIFICATE, xcred);
 	return 0;
 }
 
@@ -50,7 +72,6 @@ void session_destroy(struct session *sess)
 {
 	gnutls_bye(sess->session, GNUTLS_SHUT_WR);
 	gnutls_deinit(sess->session);
-	gnutls_certificate_free_credentials(sess->xcred);
 	free(sess);
 }
 
diff --git a/tls.go b/tls.go
index d172f8b..b243ab3 100644
--- a/tls.go
+++ b/tls.go
@@ -107,11 +107,15 @@ func Listen(network, addr string, cfg *Config) (net.Listener, error) {
 
 // Server create a server TLS Conn on c
 func Server(c net.Conn, cfg *Config) (*Conn, error) {
+	if cfg == nil {
+		return nil, errors.New("config is needed")
+	}
+
 	var sess = C.init_gnutls_server_session()
+
 	conn := &Conn{c: c, sess: sess, cfg: cfg, lock: new(sync.Mutex)}
-	n := C.size_t(uintptr(unsafe.Pointer(conn)))
-	//log.Println("conn addr ", int(n))
-	C.set_data(sess, n)
+
+	C.set_data(sess, C.size_t(uintptr(unsafe.Pointer(conn))))
 	C.set_callback(sess)
 
 	if cfg.NextProtos != nil {
@@ -126,11 +130,12 @@ func Server(c net.Conn, cfg *Config) (*Conn, error) {
 // Client create a client TLS Conn on c
 func Client(c net.Conn, cfg *Config) (*Conn, error) {
 	var sess = C.init_gnutls_client_session()
+
 	conn := &Conn{c: c, sess: sess, cfg: cfg, lock: new(sync.Mutex)}
-	n := C.size_t(uintptr(unsafe.Pointer(conn)))
-	//log.Println("conn addr ", int(n))
-	C.set_data(sess, n)
+
+	C.set_data(sess, C.size_t(uintptr(unsafe.Pointer(conn))))
 	C.set_callback(sess)
+
 	if cfg != nil {
 		if cfg.ServerName != "" {
 			srvname := C.CString(cfg.ServerName)
@@ -480,3 +485,8 @@ func onCertSelectCallback(ptr unsafe.Pointer, hostname *C.char,
 	//log.Println("set pcert length 0")
 	return -1
 }
+
+func init() {
+	C.init_xcred()
+	C.init_priority_cache()
+}