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

From: Nick Lamb <[email-masked]>
Date: Sun, 25 Nov 2018 17:18:56 +0000

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'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.

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.

Nick.

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From: Stephen Farrell <[email-masked]>
Date: Mon, 26 Nov 2018 22:08:34 +0000

>    DNS attacks by attackers on the local network, which is a common case

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.

> 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.

> 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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> [email-masked]
> https://www.ietf.org/mailman/listinfo/tls
>

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From: Eric Rescorla <[email-masked]>
Date: Mon, 26 Nov 2018 14:43:01 -0800

>    DNS attacks by attackers on the local network, which is a common case

https://github.com/tlswg/draft-ietf-tls-esni/commit/1ed8d7d02c3b0884ac20c93f891d2745ab0f9d49

-Ekr

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From: Eric Rescorla <[email-masked]>
Date: Mon, 26 Nov 2018 14:43:46 -0800

> similarly mitigated by DNSSEC.

Actually, these local attacks are better mitigated by DoH/DoT, because
what you want is to conceal the name you are looking up.

-Ekr