[Ntp] Antw: [EXT] Danny's Review (was Re: draft‑ietf‑ntp‑roughtime‑05: tag change makes implementation more complex)

Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de> Mon, 04 October 2021 07:28 UTC

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Date: Mon, 04 Oct 2021 09:28:15 +0200
From: "Ulrich Windl" <Ulrich.Windl@rz.uni-regensburg.de>
To: <watsonbladd@gmail.com>,<mayer@pdmconsulting.net>
Cc: "Marcus Dansarie" <marcus@dansarie.se>,<taralx@gmail.com>, "ntp@ietf.org" <ntp@ietf.org>
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>>> Watson Ladd <watsonbladd@gmail.com> schrieb am 28.09.2021 um 03:48 in
Nachricht
<CACsn0cmks2fdwem1rS+QNzCL1WhNR4890Fi1zpjQrL=E3Y=3fQ@mail.gmail.com>om>:
...
>> 9. Hashing algorithm in Section 6.3
>>
>> It's not clear why the algorithm can only be SHA‑512. This really should
>> be separately referenced so that if SHA‑512 is considered too week in
>> can be replaced by a different hashing algorithm like say HMAC‑SHA‑512,
>> without having to update the proposed RFC.
> 
> Part of what is required for roughtime is interoperability between all
> servers, auditors, and clients. Using only a single hash function and
> signature, and then migrating entire versions, is a better approach
> than permitting everything.

Why not specify that the only supported hash algorithm for this protocol
version is SHA-512, while later protocol version might require or support
different algorithms?
For completeness the used/expected hash algorithm could indicated by a tag
even in this version, maybe providing a mechanism how to allow/require
different algorithms in a later version.
That design would avoid some bad compatibility designs in a later version
(like NTP's "famous" extension fields).

...

Regards,
Ulrich Windl