nts: add NTS-NTP server and client

Add support for the NTS NTP extension fields.

nts_ntp_auth.h

@@ -0,0 +1,43 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * 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.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header for NTS Authenticator and Encrypted Extension Fields
+  extension field
+  */
+
+#ifndef GOT_NTS_NTP_AUTH_H
+#define GOT_NTS_NTP_AUTH_H
+
+#include "ntp.h"
+#include "siv.h"
+
+extern int NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
+                              const unsigned char *nonce, int nonce_length,
+                              const unsigned char *plaintext, int plaintext_length,
+                              int min_ef_length);
+
+extern int NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
+                             int ef_start, unsigned char *plaintext, int buffer_length,
+                             int *plaintext_length);
+
+#endif