Re: [dispatch] DISPATCH IETF 111 meeting

I hate sending symmetric keys around as much as the next person.  But we
should be pragmatic here.

The situation with SDES is unlike the situation with a bunch of the other
deprecations we have done recently (SSLv3, TLS 1.0).  There, the protocol
was broken, in the sense that it does not provide the guarantees that it is
supposed to provide.  Here, SDES still does what it says on the label, just
like it always has; we’re just increasingly grumpy about that model and
there are somewhat better alternatives.

Note “somewhat” — DTLS-SRTP is only better than SDES to the extent that the
certificates in the DTLS exchange are verified independent of the signaling
path.  If you rely only on the fingerprint in SDP for authentication, then
an SDP-path entity can swap out fingerprints to intercept get keys just as
well as with SDES.  (At best, this swaps an active for a passive attack,
which is not nothing, but not a huge step.)  We do have mechanisms for such
verification, but they’re not widely deployed.

All of which tells me that there's not an urgent need for action here.
SDES is not a looming threat to the Internet.  In the many deployments
where it is used, it still does what it claims to do, and people have
accommodated that into their broader system models.  Even if there were to
be a mass migration to DTLS-SRTP, the actual security benefit for all that
work would be fairly minor until we do a lot more work to solve the
authentication problems.

So if folks want to make a bigger, scarier warning label to put on SDES to
guide people away from it, sure, fine.  But it doesn’t seem like a blaring
red warning light is called for.  In terms of this document, the content is
probably mostly OK if we reframe it in that light.  Obsoleting SDES and
marking it Historic, though, is over the top; it will just create
unnecessary consternation.

--Richard

On Tue, Jul 27, 2021 at 7:08 PM John Mattsson <john.mattsson=
40ericsson.com@dmarc.ietf.org> wrote:

> westhawk thp@westhawk.co.uk wrote:
>
>
>
> >> On 26 Jul 2021, at 23:30, Kirsty P <Kirsty.p=40ncsc.gov.uk@dmarc.ietf.org> <&lt;Kirsty.p=40ncsc.gov.uk@dmarc.ietf.org&gt;> >wrote:
>
> >>
>
> >> SDP Security Descriptions is NOT RECOMMENDED and Historic: consensus was >sub-optimal. There was support for revisiting the space currently standardised >by SDP, but not on direction (whether to do a deprecation with/without >replacement). Future paths suggested included: mmusic, a new WG, more work >required for it to be ready, or a BoF (said in chat) to vet the idea further.
>
> >My sense is that there was a rough consensus around a goal to make it possible >to deprecate SDES - but the required steps were unclear.
>
>
>
> Yes, looking at the Jabber log there was quite strong support for the goal
> of deprecating SDES:
>
>
>
> Eric Rescorla: Let's all just agree that this (Mattson's SDES) draft is a
> good idea and promote it to full standard toda
> Martin Thomson: now that I see John presenting this, I have to wonder: why
> didn't this deprecation happen before?
> Sean Turner: When Dan Wing got up and said not to use SDES in Berlin - I
> assumed that was that ;)
> Pete Resnick: Why "NOT RECOMMENDED" instead of "MUST NOT"?
> Sean Turner: +1 to what ekr said
> Rich Salz: +1 also
>
>
>
>
>
> Regarding the next required steps I agree with Pete. Let’s charter.
>
>
>
> Ben Kaduk: So is this dispatch to BoF, or straight to WG?
>
> Pete Resnick: @ben: Sounds like this discussion has done the equivalent
> of BoFing. Charter.
>
>
>
> Cheers,
>
> John
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Re: [dispatch] DISPATCH IETF 111 meeting - preliminary outcomes and draft minutes