Re: Proposal: Run QUIC over DTLS

Eric Rescorla <ekr@rtfm.com> Tue, 06 March 2018 01:59 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Mon, 5 Mar 2018 17:58:46 -0800
Message-ID: <CABcZeBPEPuOGQZ8ZXTz0Qgcs=Lj1H21_gsPFDZC329kBMTTHPw@mail.gmail.com>
Subject: Re: Proposal: Run QUIC over DTLS
To: Mark Nottingham <mnot@mnot.net>
Cc: IETF QUIC WG <quic@ietf.org>, Lars Eggert <lars@eggert.org>
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On Mon, Mar 5, 2018 at 5:46 PM, Mark Nottingham <mnot@mnot.net>; 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?
>

Willdo. It would be especially helpful to have clarifying questions soonish
so that I can either clarify them on-list, or know to hit them in the preso.

-Ekr


>
> 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/
>
>