Re: [Ntp] I-D Action: draft-ietf-ntp-update-registries-09.txt

[Miroslav Lichvar <[e-mail]>]

On Thu, Dec 07, 2023 at 12:24:43AM -0800, Hal Murray wrote:
> 
> Ulrich Windl said:
> >       In NTPv4, one or more extension fields can be inserted after the
> >       header and before the MAC, which is always present when an
> >       extension field is present." 
> 
> I believe that's a bug in RFC 7822.

That's the OLD text of RFC 5905 updated by the RFC 7822 to:

   In NTPv4, one or more extension fields can be inserted after the
   header and before the MAC, if a MAC is present.

> > If the extension field requires a MAC, the extension field specification MUST
> > define the algorithm to be used to create the MAC and the length of the MAC
> > thus created. An extension field MAY allow for the use of more than one
> > algorithm, in which case the information about which algorithm was used MUST
> > be included in the extension field itself.
> 
> In modern practice, there is no need for the algorithm on the wire.  When you are setting up a shared key, in addition to the keyid and key itself, you have to agree on the algorithm.

That section is about potential extension fields requiring a MAC. IIRC
there is no such thing yet.

-- 
Miroslav Lichvar