NTS-KE: NTS Key Establishment

NTS-KE is the TLS v1.3 based first phase of NTS used to acquire parameters for the following NTPv4 phase securely.

Due to its TLS v1.3 nature it is hard to watch in Wireshark.

Wireshark Dissector

There is an excellent one at https://github.com/vgiotsas/NTS-KE-Dissector. Only problems:

• it's for Draft version 28 - the protocol used is 4430 instead of the 4460 from the final RFC 8915
• its showing the NTS Cookies as strings instead of hex strings

So - this repo contains the original version + my patches.

Recording TLS v1.3

• make the TLS library used record the ephemeral keys and parameters
• depends on the NTS client used (my chrony used GnuTLS, ntpd used OpenSSL)
  • sometimes you can use environment variable SSLKEYLOGFILE out-of-the box
  • if this doesn't work, create a shared library that instruments the TLS library used to record this file and then preload it via LD_PRELOAD
    • OpenSSL: SSL_CTX_set_keylog_callback from here
    • GnuTLS: gnutls_global_set_log_function from here
• after you did this, the TLS parameters are written to this file
• make Wireshark use this file as TLS (Pre)-Master Secret Log File under Settings | Protocols | TLS
• invoke the NTS client and record the whole TLSv1.3 handshake
• with the dissector loaded (put it into your Lua plugins directory, see Help | About | Folders), you can now dissect NTS-KE

Sample Files

Repository contains a nts-ke.pcapng and tls-secrets.txt to load into your Wireshark.

Should look like this