Re: Proposal: Run QUIC over DTLS

Mirja Kühlewind <mirja.kuehlewind@tik.ee.ethz.ch> Tue, 13 March 2018 18:30 UTC

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Subject: Re: Proposal: Run QUIC over DTLS
To: Mark Nottingham <mnot@mnot.net>, Eric Rescorla <ekr@rtfm.com>
Cc: Lars Eggert <lars@eggert.org>, IETF QUIC WG <quic@ietf.org>
References: <CABcZeBO9g5vnPK2aGYEUOYOkT-898Gc0-d4T=kDvxuE2Yg6kMQ@mail.gmail.com> <1F5ABFEF-64F2-4A53-A35B-DF8A4A2A4446@mnot.net>
From: =?UTF-8?Q?Mirja_K=c3=bchlewind?= <mirja.kuehlewind@tik.ee.ethz.ch>
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Date: Tue, 13 Mar 2018 19:30:20 +0100
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Hi Mark,

coming back to this initial mail, I believe that it is clear that people 
are interested in the problem(s) that this proposal is addressing but 
not the actually solution as there is a strong feeling that it is too 
late for such a fundamental change in the process.

I just looked at the draft agenda and it (still) say "QUIC over DTLS 
Proposal". Is there a plan to change this and level this up to a more 
higher level discussion on the problems or do people still want to use 
the time to discuss this concrete proposal?

Mirja


On 06.03.2018 02:46, Mark Nottingham wrote:
> Thanks for the proposal, EKR. We'll track this as <https://github.com/quicwg/base-drafts/issues/1165>;.
> 
> Since we're trying to nail down the invariants in London (or soon afterwards), I'd like to figure out the WG's feelings on this pretty quickly.
> 
> I know folks need a chance to read and digest, but it would be extremely helpful if we could have some initial discussion on-list now. Please focus on the technical merit of the proposal, clarifying questions, and statements of support/lack thereof.
> 
> Assuming it's still a topic of interest in two weeks, we'll schedule some time to discuss it in London. EKR, could you please submit a presentation (say, max 20 minutes, plus discussion time afterwards) ASAP?
> 
> Cheers,
> 
> 
>> On 6 Mar 2018, at 10:05 am, Eric Rescorla <ekr@rtfm.com>; wrote:
>>
>> Hi folks,
>>
>> Sorry to be the one randomizing things again, but the asymmetric
>> conn-id thing went well, so here goes....
>>
>> TL;DR.
>> I'd like to discuss refactoring things to run QUIC over DTLS.
>>
>> DETAILS
>> When we originally designed the interaction between TLS and QUIC,
>> there seemed like a lot of advantages to embedding the crypto
>> handshake on stream 0, in particular the ability to share a common
>> reliability and congestion mechanism. However, as we've gotten further
>> along in design and implementation, it's also become clear that it's
>> archictecturally kind of crufty and this creates a bunch of problems,
>> including:
>>
>>    * Stream 0 is unencrypted at the beginning of the connection, but
>>      encrypted after the handshake completes, and you still need
>>      to service it.
>>
>>    * Retransmission of stream 0 frames from lost packets needs special
>>      handling to avoid accidentally encrypting them.
>>
>>    * Stream 0 is not subject to flow control; it can exceed limits and
>>      goes into negative credit after the handshake completes.
>>
>>    * There are complicated rules about which packets can ACK other
>>      packets, as both cleartext and ciphertext ACKs are possible.
>>
>>    * Very tight coupling between the crypto stack and the transport
>>      stack, especially in terms of knowing where you are in the
>>      crypto state machine.
>>
>> I've been looking at an alternative design in which we instead adopt a
>> more natural layering of putting QUIC on top of DTLS. The basic
>> intuition is that you do a DTLS handshake and just put QUIC frames
>> directly in DTLS records (rather than QUIC packets). This
>> significantly reduces the degree of entanglement between the two
>> components and removes the corner cases above, as well as just
>> generally being a more conventional architecture. Of course, no design
>> is perfect, but on balance, I think this is a cleaner structure.
>>
>> I have a draft for this at:
>> https://datatracker.ietf.org/doc/draft-rescorla-quic-over-dtls/
>>
>> And a partial implementation of it in Minq at:
>>
>> Mint: https://github.com/ekr/mint/tree/dtls_for_quic
>> Minq: https://github.com/ekr/minq/tree/quic_over_dtls
>>
>>
>> I can't speak for anyone else's implementation, but at least in my
>> case, the result was considerable simplification.
>>
>> It's natural at this point to say that this is coming late in the
>> process after we have a lot invested in the current design, as well as
>> to worry that it will delay the process. That's not my intention, and
>> as I say in the draft, many of the issues we have struggled over
>> (headers especially) can be directly ported into this architecture (or
>> perhaps just reused with QUIC-over-DTLS while letting ordinary DTLS do
>> its thing) and this change would allow us to sidestep issued we are
>> still fighting with, so on balance I believe we can keep the schedule
>> impact contained.
>>
>> We are designing a protocol that will be used long into the future, so
>> having the right architecture is especially important. Our goal has
>> always been to guide this effort by implementation experience and we
>> are learning about the deficiencies of the Stream 0 design as we go
>> down our current path. If the primary concern to this proposal is
>> schedule we should have an explicit discussion about those relative
>> priorities in the context of the pros and cons of the proposal.
>>
>> The hackathon would be a good opportunity to have a face to face chat
>> about this in addition to on-list discussion.
>>
>> Thanks in advance for taking a look,
>> -Ekr
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
> 
> --
> Mark Nottingham   https://www.mnot.net/
>