Re: [TLS] Fwd: Re: AD review of draft-ietf-tls-dtls-connection-id-07

Benjamin Kaduk <kaduk@mit.edu> Wed, 14 October 2020 21:20 UTC

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Date: Wed, 14 Oct 2020 14:20:09 -0700
From: Benjamin Kaduk <kaduk@mit.edu>
To: Achim Kraus <achimkraus@gmx.net>
Cc: draft-ietf-tls-dtls-connection-id@ietf.org, "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] Fwd: Re: AD review of draft-ietf-tls-dtls-connection-id-07
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On Tue, Oct 13, 2020 at 06:50:52AM +0200, Achim Kraus wrote:
> Hi Ben,
> 
> > Sure, there's pretty standard common-knowledge guidance, though I'm not
> > sure it's documented anyplace particularly discoverable:
> >
> > - include in the MAC as much application/protocol context and protocol
> >    fields as you can without breaking operation of the procotol
> > - ensure that the mapping from (set of protocol fields and values derived
> >    from application context) to (bytes given as input to the MAC function) is
> >    an injective mapping
> >
> > In some (many?) cases, there is not any additional contextual information
> > available, and the protocol header itself has a deterministic/fixed-length
> > encoding, so both points can be achieved by just using the protocol
> > header/payload as it appears on the wire as MAC input.  For better or for
> > worse, the current construction in the -07 diverges significantly from the
> > actual protocol header, so we have to do a bit of thinking to ensure that
> > we are compliant to the guidelines (that I just described, so I assume you
> > did not previously think about them in that formulation).
> >
> 
> Hope, I'm not again catched by my bad english :-):

Sorry, my writing became less clear when I attempted to edit it :(

> If the forumlation refers to draft-ietf-tls-dtls-connection-id-07 (and
> not my e-mails), I can't say, what was thought or not by the authors. My
> role in that discussion quite a year ago, was just to ask, which of the
> many variants should then be chosen in order not to change it every year.

I was just saying "I only told you the list of two things that are the
standard guidance just now; I don't expect that you used those two things
as part of your thought processes before I told them to you".

-Ben