Re: Benjamin Kaduk's Discuss on draft-ietf-quic-transport-33: (with DISCUSS and COMMENT)

Martin Duke <> Fri, 08 January 2021 19:18 UTC

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From: Martin Duke <>
Date: Fri, 08 Jan 2021 11:18:27 -0800
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Subject: Re: Benjamin Kaduk's Discuss on draft-ietf-quic-transport-33: (with DISCUSS and COMMENT)
To: Spencer Dawkins at IETF <>
Cc: Benjamin Kaduk <>, Lars Eggert <>, WG Chairs <>, IETF QUIC WG <>, The IESG <>,
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Downgrade is a problem even if v2 offers no security improvements. For
instance, a middlebox might want to inspect v1 Initials and force
downgrades, which would prevent deployment of new versions.

On Fri, Jan 8, 2021 at 11:15 AM Spencer Dawkins at IETF <> wrote:

> Hi, Ben,
> Top-posting here - I think one other point that is worth remembering, is
> that the QUIC working group also has
>, which
> seems like a fine place for recommendations about deployment of specific
> versions and withdrawal of other versions.
> In my mind, there are two cases. Either
>    - QUICv1 is "secure enough", so using it is OK even if QUICv2 would be
>    better, or
>    - QUIVv1 is not "secure enough", so downgrading will be a problem.
> People can deploy QUIC using a variety of implementation strategies, but
> given that the QUIC implementation is likely at least a library, and may be
> a library bound to a specific application, it would be reasonable to say
> "QUICv1 is not secure enough, so stop using QUICv1 as soon as possible",
> and let implementers and deployers put out versions of applications that
> aren't bound to QUICv1 at all.
> (This discussion is slightly weird to me, because the last time I asked
> about "QUICv2", the answer I got was that we're more likely to run for some
> time with QUIv1 + extensions, but even then, my intention when QUIC was
> chartered, was that deploying new versions should be orders of magnitude
> than the universal deployment of a new version of TCP, for instance, and
> withdrawing QUICv1 should be a lot easier than withdrawing TCPv4).
> I'm sure everyone will Do The Right Thing, of course.
> Best,
> Spencer
> On Thu, Jan 7, 2021 at 5:18 PM Benjamin Kaduk <> wrote:
>> Thanks everyone for the productive discussion.  It's clear that there's
>> a lot of background available to those who participated in the previous
>> WG discussions but (understandably!) did not make it into the document
>> itself, and I appreciate the effort that was put in to help share that
>> with
>> me.
>> Just to state it clearly, at no point has my position been that QUIC v1
>> needs to be delayed until a complete version negotiation story exists.
>> As this was a "discuss discuss", my goal was to obtain more information
>> about the actual situation in order to confirm that there are no
>> significant issues, since my interpretation of the text in the document
>> itself left that possibility open.
>> Attempting to summarize salient points:
>> - the IETF is only currently defining bindings for HTTP over QUIC,
>>   though other entities are free to define their own protocol over QUIC
>>   at any time.
>> - the only way currently defined to discover a QUIC endpoint to use as
>>   server for a given HTTP service is the Alt-Svc header field, which
>>   uses an ALPN value to indicate the protocol to use; it is perhaps not
>>   fully nailed down that the ALPN value will be specific to a particular
>>   version of QUIC but the ALPN vlaue probably will be specific to a
>>   particular version of QUIC.
>> - (SVCB is in the works, too, but may not be able to meet all the needs
>>   for this purpose.)
>> - Anyone doing non-HTTP or non-Alt-Svc is presumed to be configuring it
>>   out of band and thus can provision the QUIC version to use along with
>>   other provisioned information; in-band version negotiation is not
>>   needed in that case.  If needed (e.g., we cannot build a secure
>>   downgrade protection mechanism), this or similar techniques could be
>>   used generically.
>> - A downgrade protection mechanism solely in-band at the QUIC layer will
>>   not be a complete solution for existing protocols that may also fall
>>   back to a TCP binding (or new protocols that need to traverse networks
>>   like the Internet that don't reliably pass UDP in the ways QUIC
>>   needs).  New protocols over QUIC that are berift of such legacy would
>>   have a complete solution, though.
>> - There seems to be a desire to have only zero or one functional downgrade
>>   prortection/version negotiation mechanism, globally.
>> - (There is a corresponding desire to have zero non-functional downgrade
>>   protection/version negotiation mechanisms.)
>> - In accordance with the previous two points, it's expected that a
>>   downgrade protection/version negotiation scheme, when specified, will
>>   be in an IETF standards-track protocol specification.  (This document
>>   does not necessarily have to be a new QUIC version, as I understand it,
>>   though is not a blocking dependency until there is such a new version.)
>> - In particular, we do *not* expect non-IETF QUIC versions to define
>>   their own downgrade protection scheme.  They are expected to either
>>   pick up the IETF one (when it exists) or just only use a single
>>   version at a time, possibly with out of band configuration.
>> I've attempted to update the text in the document to reflect my
>> understanding of the current WG expectations (as summarized above), in a
>> PR at .
>> Obviously, if my summary above is incorrect, that PR is not expected to
>> be useful.
>> In particular, since we do *not* expect or want non-IETF QUIC versions
>> to be attempting to specify a downgrade protection scheme, the scope of
>> the problem space seems sufficiently restricted that we have ample time
>> to come up with something good and not find ourselves reacting to events
>> out of our control.  The phrasing in the -33 suggests, at least to me,
>> that *any* future version of QUIC, including one developed outside the
>> IETF, might update version negotiation handling, which is where my
>> perception of risk arose.
>> I've tried to refrain from expounding on topics that are not actually
>> relevant, but since I'm prone to doing so I may have let some sneak in
>> anyway...
>> Thanks again,
>> Ben