[Ntp] NTS for PTP feedback

David Venhoek <david@venhoek.nl> Thu, 01 February 2024 14:46 UTC

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From: David Venhoek <david@venhoek.nl>
Date: Thu, 01 Feb 2024 15:45:48 +0100
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Subject: [Ntp] NTS for PTP feedback
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Hi All,

I've worked through the nts for ptp draft today in preparation for
also making a proof of concept implementation in statime. Below a
number of comments on the current draft. Note that my focus currently
was on multicast only, so I haven't looked in detail yet at the
unicast-specific parts.

Kind regards,
David Venhoek

Major issues
In section 2.1, the draft states: "THEN the server requests the
client's X.509 certificate (via TLS Certificate Request)" (emphasis
added), after data is already exchanged over the TLS session. Since
TLS 1.3 there is no longer any support for a renegotiation during a
TLS session, hence this seems to not be possible within the TLS spec.
Do you mean that before honoring the request the server should check
that the client authenticated with a valid certificate during the
initial handshake?

Section 2.1.1 refers to "The group number", but this is neither
defined in the PTP specification, nor earlier in this document. What
is it? it seems to be very similar to the SPP defined in
IEEE1588-2019, why do we need it?

The fields in section 3.2.11 are not aligned. This can be problematic
when implementing on platforms like ARM.

Per 16.14.2 of IEEE1588-2019, the key management mechanism should
provide a sequenceID window, but the specification doesn't state how
this is provided.

General remarks
Draft allocates concrete numbers in ranges not reserved for
experimental or private use, rather than waiting for IANA assignment.
I would suggest removing the concrete values for now, suggesting
experimental use numbers for draft implementations.

Draft repeats the same subject multiple times and is in general quite
all over the place.

General language use around the "messages" is unclear. What is a
message, what is a record structure in this context?

There also seems a lot of repetition of structures and information
already standardised in other specifications. I would suggest mostly
removing this and refering to the relevant specifications. In
particular, I would avoid including full tables of identifiers defined
accross multiple standards.