Re: [Resolverless-dns] Paper on Resolver-less DNS

Erik Sy <sy@informatik.uni-hamburg.de> Thu, 29 August 2019 14:36 UTC

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References: <CAHbrMsBhR1yaLxQk7wZk54Jdf5nvkS03KC3UTae0Famu2+SV8g@mail.gmail.com> <4568720.uvMTqBdgP4@linux-9daj> <fb12f102-714d-95cc-c6cc-0871a2df9f50@informatik.uni-hamburg.de> <34813218.VKkrhzyXsx@linux-9daj> <ae355776-a1bb-cf23-f380-133439661d1f@informatik.uni-hamburg.de> <1171283855.590.1566558699991@appsuite-gw1.open-xchange.com> <a8d9398b-4fea-0a1e-3fa7-5954d001f9ea@informatik.uni-hamburg.de> <1405682425.665.1566561941610@appsuite-gw1.open-xchange.com> <220061a8-608c-0a87-4656-213c87979284@informatik.uni-hamburg.de> <849BE7D4-A07E-496B-B413-E1C979390DA8@osterweil.net> <b2b3e56a-c577-f08a-627a-f54e2e6fadb6@informatik.uni-hamburg.de> <f093a605-6e7d-0237-df5c-441d6789c66f@erik-sy.de> <54892F22-27E4-4444-9CC8-2D9E84A9668F@dukhovni.org>
From: Erik Sy <sy@informatik.uni-hamburg.de>
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Date: Thu, 29 Aug 2019 16:36:42 +0200
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Subject: Re: [Resolverless-dns] Paper on Resolver-less DNS
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On 8/27/19 23:39, Viktor Dukhovni wrote:
>> On Aug 27, 2019, at 5:18 PM, Erik Sy <email@erik-sy.de> wrote:
>>
>> It seems to me, that both of you are OK with the risk of DNSSEC + DANE
>> TLSA leading to hard failures.
> I also deny beating my spouse...  Seriously, the premise of the question
> "are you OK with the risk of DANE leading to hard failures" is flawed.
> Hard failures are the purpose of security mechanisms.  Of course I am
> OK with a security mechanism that may deny access, that's not the
> right question.

I disagree, that this question is flawed. It assumes that DNSSEC + DANE
is an optional security mechanism in the context of web browsers. Note,
that for example a valid TLS certificate is considered a mandatory
security mechanism and should be enforced by hard failures. Thus, the
question is more like "are you OK with optional security mechanisms
leading to hard failures".

>
> The right question is whether a given mechanism is sufficiently robust
> to be usable. 
At least the given mechanism needs also to provide a significant
security benefit. In my view, the additional benefit of DNSSEC+ DANE
compared to Certificate Transparency + Strict Transport Security (HSTS
or MTA-STS) is for the majority of server operators or users not relevant.
>> I like to point out, that resolver-less DNS can be extended to support
>> DNSSEC + DANE TLSA as a validation mechanism for DNS records. Thus, in
>> case browser vendors decide to support DNSSEC + DANE TLSA the browsers
>> can receive the corresponding records also via resolver-less DNS.
> Actually, we've been down that road already (TLS DNSSEC chain
> extension fiasco).  There is no clean way to provide downgrade
> resistance in such a protocol, or even properly ensure that
> answers are in bailiwick.  I doubt you are proposing that servers
> MUST always return a full DNSSEC validation chain for the returned
> RRsets (or denial of existence proofs for the associated DS RRs).

In my view, supporting DNSSEC + DANE TLSA in resolver-less DNS makes
only sense if the server provides a full DNSSEC validation chain because
everything else seems to introduce significant delays. However, given
the significant size of full DNSSEC validation chains such feature
should be deactivated in a default configuration of resolver-less DNS.
Anyway, as long as no web browser intends to support a validation of DNS
records via DNSSEC + DANE TLSA, there is no requirement for
resolver-less DNS to support this practice.

Erik