Re: [TLS] Dnsdir early review of draft-ietf-tls-svcb-ech-01

[Rob Sayre <[e-mail]>]

Yeah, that sounds fine. I think 9460 is pretty good in that it covers both
DNSSEC and encrypted transports for DNS.

thanks,
Rob


On Sat, Mar 30, 2024 at 10:27 AM Ted Lemon <[e-mail]> wrote:

> I think that would make sense, yes.
>
> On Sat, Mar 30, 2024 at 10:58 AM Erik Nygren <[e-mail]> wrote:
>
>> Do we want a few sentences in Security Considerations that references
>> https://www.rfc-editor.org/rfc/rfc9460.html#section-3.1 to call this out?
>>
>> This seems like something that became less clear when we split these two
>> docs apart.
>> Most of draft-ietf-tls-svcb-ech used to be a section of what is now
>> rfc9460 but got split out
>> due to publication timelines.  It may be that some non-normative
>> references back to rfc9460
>> might help readers not miss things like this which might have been more
>> clear when they
>> were a single document.
>>
>>    Erik
>>
>>
>>
>>
>> On Fri, Mar 29, 2024 at 11:31 PM Ted Lemon <[e-mail]> wrote:
>>
>>> Yes, that fully addresses my concern. Thanks!
>>>
>>> Op vr 29 mrt 2024 om 22:54 schreef Eric Rescorla <[e-mail]>
>>>
>>>>
>>>> Hi Ted,
>>>>
>>>> Doesn't this section of RFC 9460 address this case and say what you are
>>>> recommending:
>>>>
>>>> https://www.rfc-editor.org/rfc/rfc9460.html#section-3.1
>>>>
>>>> -Ekr
>>>>
>>>>
>>>>
>>>> On Fri, Mar 29, 2024 at 6:49 PM Ted Lemon <[e-mail]> wrote:
>>>>
>>>>> Okay, I think I see the disconnect, maybe. The issue I'm pointing to
>>>>> is that you may or may not be doing DNSSEC validation. And you may or may
>>>>> not be /able/ to do DNSSEC validation if the infrastructure breaks it
>>>>> accidentally or deliberately.
>>>>>
>>>>> The document says: "The SVCB-optional client behavior specified in
>>>>> (Section 3 of [SVCB]) permits clients to fall back to a direct connection
>>>>> if all SVCB options fail. This behavior is not suitable for ECH, because
>>>>> fallback would negate the privacy benefits of ECH."
>>>>>
>>>>> So it's saying that the default handling of SVCB is incorrect and
>>>>> would fail open, and overriding that behavior. Given that this is the case,
>>>>> that implies that it matters whether the data has been validated, but
>>>>> nowhere in the document, certainly not in Security Considerations, is any
>>>>> mention made of this issue. So that's what I'm pointing out.
>>>>>
>>>>> It is absolutely not the case in practice that all stub resolvers do
>>>>> validation. You are making a security decision about trust based on data
>>>>> the trustworthiness of which you've not discussed, in a situation where the
>>>>> implementor has meaningful choices to make with respect to validating that
>>>>> trustworthiness. So it's worth mentioning that if the policy is not to
>>>>> validate, this vulnerability exists.
>>>>>
>>>>> I'm a DNS guy, not a TLS guy, so I don't know the history of this
>>>>> work—I'm just making this observation about the document I was asked to
>>>>> review. The fact that (apparently) no DNSDIR review ever raised this issue
>>>>> about the other documents you mentioned is of no interest to me—I'm not
>>>>> reviewing those documents.Whether you take this advice is between you and
>>>>> the IESG. I'm not even claiming to be right—just pointing out the issue I
>>>>> see.
>>>>>
>>>>> On Fri, Mar 29, 2024 at 7:21 PM Rob Sayre <[e-mail]> wrote:
>>>>>
>>>>>> I don't think it relates to DNSSEC. You can fail at DNS (DNSSEC
>>>>>> failure) or you can fail during ECH (unless you want to use non-ECH, which
>>>>>> is not ECH, and not part of this draft).
>>>>>>
>>>>>> It makes sense to me: one can reject a request unless the
>>>>>> requirements embedded in the SVCB are met (the server chooses those, which
>>>>>> can include many aspects of the request). I don't understand why one would
>>>>>> insert DNSSEC here. That seems to be the whole point--it works without it.
>>>>>>
>>>>>> thanks,
>>>>>> Rob
>>>>>>
>>>>>>
>>>>>> On Fri, Mar 29, 2024 at 3:57 PM Ted Lemon <[e-mail]> wrote:
>>>>>>
>>>>>>> I'm not telling you that you have to require DNSSEC. I'm saying the
>>>>>>> document is incomplete if you don't talk about how it relates to DNSSEC. I
>>>>>>> think EKR got the point, so maybe go with his approach?
>>>>>>>
>>>>>>> On Fri, Mar 29, 2024 at 6:27 PM Rob Sayre <[e-mail]> wrote:
>>>>>>>
>>>>>>>> It's a policy choice, though, right? I think ekr hinted at this
>>>>>>>> issue as well.
>>>>>>>>
>>>>>>>> It's that one might also view requests that reveal the SNI as
>>>>>>>> insecure. If that's the case, DNSSEC doesn't help. There will certainly be
>>>>>>>> a transition period where that will be impractical for many servers. I
>>>>>>>> think these are separate problems, though.
>>>>>>>>
>>>>>>>> thanks,
>>>>>>>> Rob
>>>>>>>>
>>>>>>>>
>>>>>>>> On Fri, Mar 29, 2024 at 3:10 PM Ted Lemon <[e-mail]> wrote:
>>>>>>>>
>>>>>>>>> It looks like if you can't get the SCVB you're going to fail
>>>>>>>>> insecure, so being able to use DNSSEC to prevent that for signed domains
>>>>>>>>> seems worthwhile.
>>>>>>>>>
>>>>>>>>> On Fri, Mar 29, 2024 at 4:41 PM Rob Sayre <[e-mail]>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> On Fri, Mar 29, 2024 at 1:02 PM Ted Lemon via Datatracker <
>>>>>>>>>> [e-mail]> wrote:
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> I don't think it's reasonable to specify the privacy properties
>>>>>>>>>>> of SVCB and
>>>>>>>>>>> /not/ talk about DNSSEC validation.
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Could you explain more about this part? I think DNSSEC doesn't
>>>>>>>>>> add much here, unless you want to accept non-ECH traffic. For example, many
>>>>>>>>>> of the test servers will bounce you to some other site if you don't send
>>>>>>>>>> ECH or screw it up in some way (speaking as someone who has screwed it up
>>>>>>>>>> many times...).
>>>>>>>>>>
>>>>>>>>>> I think there might be a DoS attack here, where someone messes
>>>>>>>>>> with the response, but they can also turn off the DNSSEC bit unless it's
>>>>>>>>>> DoT/DoH/DoQ etc. So, if using those, it's just the trustworthiness of the
>>>>>>>>>> DNS server itself, right? Sorry if I'm missing something.
>>>>>>>>>>
>>>>>>>>>> thanks,
>>>>>>>>>> Rob
>>>>>>>>>>
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