Re: [TLS] Mail regarding draft-ietf-tls-esni

Stephen Farrell <stephen.farrell@cs.tcd.ie> Mon, 26 November 2018 22:08 UTC

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To: Nick Lamb <njl@tlrmx.org>, tls@ietf.org
References: <20181125171856.52ba2503@totoro.tlrmx.org>
From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Date: Mon, 26 Nov 2018 22:08:34 +0000
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Subject: Re: [TLS] Mail regarding draft-ietf-tls-esni
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On 25/11/2018 17:18, Nick Lamb wrote:
> In section 7.1 the -02 draft says:
> 
>    Clearly, DNSSEC (if the client validates and hard fails) is a defense
>    against this form of attack, but DoH/DPRIVE are also defenses against
>    DNS attacks by attackers on the local network, which is a common case
>    where SNI.
> 
> Where SNI what?

I'm guessing what's missing is an argument that DoT or DoH can
(if better than opportunistic) counter some local attacks that'd be
similarly mitigated by DNSSEC.

> I'd be tempted to just say that yes, an active adversary can force you
> to choose between privacy and connectivity, and hard fail DNSSEC is the
> only existing way to choose privacy.

Perhaps (exceptionally) less so in this case. The client here
depends on confidentiality of the DNS query for both the A/AAAA
and ESNIKeys RR's, so an authenticated DoT or DoH connection
to a chosen recursive could be a pretty good defence here. And
DNSSEC alone (hard fail or not) isn't sufficient.

> The current text feels more like an attempt by people who don't want to
> face the Dancing Pig problem to justify why their latest seat-belt that
> snaps in a crash (to borrow Adam Langley's phrase) is a good idea
> anyway. But regardless of whether I'm correct about that, the sentence
> is confusing as it stands now.

FWIW, I'd have no issue with more strongly encouraging DNSSEC,
but I think ESNI turns out to be a situation where the presence
or absence of DNSSEC perhaps makes less difference that in other
TLS cases. For example, I think there's a stronger argument for
DNSSEC being used to secure CAA RRs or those used by any ACME
challenges, than there is for reasons related to ESNI.

Cheers,
S.


> 
> Nick.
> 
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