Re: Stream0 Proposal: EMPTY_ACK

[Eric Rescorla <[e-mail]>]

On Wed, May 23, 2018 at 7:10 PM, Christian Huitema <[e-mail]>
wrote:

> I dislike the EMPTY_ACK because they are "responses to something that
> could not be decrypted". You don't know where the packet came from, it
> could be spoofed. So you have on one hand a possible optimization, on the
> other hand a possible vulnerability, and in all cases additional complexity.
>
What's the vulnerability? Anything more than a spurious retransmit?

-Ekr


> On 5/23/2018 4:27 PM, Jana Iyengar wrote:
>
> (Moving more discussions from main thread)
>
> ---------- Forwarded message ----------
> From: Subodh Iyengar <[e-mail]>
> Date: Wed, May 23, 2018 at 3:37 PM
> Subject: Re: Stream0 Design Team Proposal
> To: Mike Bishop <[e-mail]>, Christian Huitema <
> [e-mail]>, "[e-mail]" <[e-mail]>
>
>
> FWIW I see EMPTY_ACKs as being very similar to a Duplicate ack. We thought
> about using Duplicate acks as well but we thought that EMPTY_ACks would be
> simpler to implement and be able to convey similar information.
>
>
> Subodh
> ------------------------------
> *From:* QUIC <[e-mail]> on behalf of Mike Bishop <
> [e-mail]>
> *Sent:* Wednesday, May 23, 2018 3:26:35 PM
> *To:* Christian Huitema; [e-mail]
> *Subject:* RE: Stream0 Design Team Proposal
>
>
> Christian, can you expand on why you dislike the EMPTY_ACK?  Being able to
> say “I’ve received some packets from you, but am unable to process any of
> them because I’m missing some handshake data” seems like a useful way to
> short-circuit timeouts on clients.  It also doesn’t commit the server to
> holding any state – IIUC, a server could form a packet containing an
> EMPTY_ACK and then discard its internal state until it gets the
> retransmitted (or delayed) Initial packet.
>
>
>
>
>
> On Wed, May 23, 2018 at 4:25 PM, Jana Iyengar <[e-mail]> wrote:
>
>> (Forking this discussion off from the main thread.)
>>
>> On Wed, May 23, 2018 at 2:13 AM, Kazuho Oku <[e-mail]> wrote:
>>
>>> 2018-05-23 14:29 GMT+09:00 Christian Huitema <[e-mail]>:
>>> > I like the proposal. In particular, I really like the encryption of
>>> > handshake packets with the handshake key, as it does close a number of
>>> > avenues for attacks. And I like that it solves the "ack promotion"
>>> issue
>>> > that I was complaining against for some time. Turns out that in the
>>> current
>>> > draft, it is very hard to contain that problem if you enable client
>>> auth.
>>> >
>>> >
>>> > On the other hand, I agree with Martin that a lot of the additions to
>>> > transmission recovery should be moved to separate PRs. I am not
>>> enthusiastic
>>> > with the EMPTY ACK mechanism, or with the proposed "implicit
>>> > acknowledgement" of a lower crypto stream by a higher level ack.
>>>
>>> At the moment I do not have a strong opinion on the Empty ACK mechanism.
>>>
>>> However, regarding how we close the Initial and Handshake contexts, my
>>> preference goes to using implicit ACKs (i.e. use the successful
>>> receipt of a packet that is protected under a higher level of
>>> encryption key as the signal) rather than explicitly ACKing the last
>>> flight of data.
>>>
>>> As I see, there are two downsides in the Explicit ACKing approach.
>>>
>>> * Explicit ACKing requires sending two additional packets during the
>>> handshake, which means that we would have more AES operations plus
>>> somewhere around 60 bytes of overhead on the wire.
>>> * Explicit ACKing requires more signaling from the TLS stack. In case
>>> of implicit ACKing, the TLS stack need to only provide the AEAD
>>> contexts and the messages, whereas in case of explicit ACKing, the TLS
>>> stack also needs to provide a signal indicating the end of the
>>> transmission at each encryption level.
>>>
>>> The downside of the implicit ACKing approach is that the server needs
>>> to signal the termination of the Handshake context using a special
>>> frame sent using a 1-RTT packet.
>>>
>>> But even taking that into consideration, I think that implicit ACKing
>>> is still easier to implement, considering the need for the additional
>>> signal in the explicit ACK case that have been described above.
>>>
>>>
>>> > In any
>>> > case, starting as simple as possible would help having the first
>>> > implementations and tests.
>>> >
>>> >
>>> > On 5/22/2018 8:26 PM, Subodh Iyengar wrote:
>>> >
>>> > As an implementor of fizz, I support this design and am willing to
>>> implement
>>> > this as well.
>>> >
>>> >
>>> > While this is a change in the API that TLS classically exposes, I
>>> think this
>>> > is the right tradeoff because it helps make things way more explicit
>>> which
>>> > will prevent several other bugs from happening in the future.
>>> >
>>> >
>>> > Subodh
>>> >
>>> > ________________________________
>>> > From: QUIC <[e-mail]> on behalf of Martin Thomson
>>> > <[e-mail]>
>>> > Sent: Tuesday, May 22, 2018 8:00:40 PM
>>> > To: Ian Swett
>>> > Cc: [e-mail]; QUIC WG
>>> > Subject: Re: Stream0 Design Team Proposal
>>> >
>>> > First of all, thanks to the design team for the work they have done.  I
>>> > haven't digested everything yet, but I think that I have a good sense
>>> of
>>> > the shape of the proposal.
>>> >
>>> > Overall, this looks like a workable design.  It's a lot more invasive
>>> of
>>> > the cryptographic handshake implementation than I had thought people
>>> were
>>> > willing to stomach originally.  But it's clear that we've run into
>>> problems
>>> > with the current, more abstract API and this is a fairly natural way to
>>> > split TLS.  I've spent a little time thinking about how this might be
>>> > implemented and I think that it's not going to be *too* painful.  The
>>> proof
>>> > will be in the pudding there though.
>>> >
>>> > In looking at the PR, I really appreciate seeing all the changes
>>> together..
>>> > BTW, the link above points to the wrong PR, so be careful (it appears
>>> to
>>> > have the same content, but that's not guaranteed).  The actual PR is
>>> here:
>>> > https://github.com/quicwg/base-drafts/pull/1377
>>> >
>>> > I've pushed a branch to the main repo so that you can preview the
>>> entire
>>> > document set:
>>> > https://urldefense.proofpoint.com/v2/url?u=https-3A__quicwg.
>>> github.io_base-2Ddrafts_stream0_&d=DwIBaQ&c=5VD0RTtNlTh3ycd4
>>> 1b3MUw&r=h3Ju9EBS7mHtwg-wAyN7fQ&m=_vGK3zTKFrMOkFihJnPntLYw1T
>>> 0_NEMiHYSM0Q_u1JA&s=ususmtxI3BTaLlBWe_HkQUWRH4sBI0Cggj1oWZMBHak&e=
>>> >
>>> > It seems like there are some core changes here and a bunch of
>>> separable or
>>> > at least secondary changes.  I'm sure that each one has its own
>>> > justification, but that isn't always clear. The following changes seem
>>> like
>>> > they are separable:
>>> >
>>> > * The use of separate packet number spaces
>>> > * The Retry packet changes (and NEW_TOKEN)
>>> > * EMPTY_ACK
>>> > * The TLS extension for flow control
>>> >
>>> > Right now, some of these appear to be entirely gratuitous.  I'd like
>>> to get
>>> > to the bottom of each before we continue.
>>> >
>>> > At a minimum, the PR we land first should include just the core
>>> changes.
>>> > As you say, reviewing a monster PR like this will only make GitHub weep
>>> > unicorns, but we might be able to cut this into smaller pieces.
>>> >
>>> > On Wed, May 23, 2018 at 11:31 AM Ian Swett <ianswett=
>>> > [e-mail]> wrote:
>>> >
>>> >> Dear QUIC WG,
>>> >
>>> >
>>> >> On behalf of the Stream 0 Design Team, I am pleased to report that we
>>> > have consensus on a proposed approach to share with the WG. The DT's
>>> > proposal will make QUIC and TLS work closer together and incorporates
>>> ideas
>>> > from DTLS, but it does not use the DTLS protocol itself.
>>> >
>>> >
>>> >> The DT believes this solves the important open Stream 0 issues. The
>>> > proposal will be a bit more invasive in TLS, but we believe it is the
>>> right
>>> > long-term direction and several TLS stacks (BoringSSL, PicoTLS, NSS,
>>> and
>>> > Mint) are willing and able to do the work necessary.. A number of
>>> stacks
>>> > are currently working on implementations of this new approach, which we
>>> > hope to have in time for the Interim meeting.
>>> >
>>> >
>>> >> A design document describing the overall approach can be found at:
>>> >
>>> >
>>> > https://urldefense.proofpoint.com/v2/url?u=https-3A__docs.go
>>> ogle.com_document_d_1fRsJqPinJl8N3b-2DbflDRV6auojfJLkxddT93j
>>> 6SwHY8_edit&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=h3Ju9EBS7mHt
>>> wg-wAyN7fQ&m=_vGK3zTKFrMOkFihJnPntLYw1T0_NEMiHYSM0Q_u1JA&s=j
>>> DNnz34hmWvLSQnHkSnYdihW-jG-0xZ-YYqKq30wVGg&e=
>>> <https://urldefense.proofpoint.com/v2/url?u=https-3A__docs..google.com_document_d_1fRsJqPinJl8N3b-2DbflDRV6auojfJLkxddT93j6SwHY8_edit&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=h3Ju9EBS7mHtwg-wAyN7fQ&m=_vGK3zTKFrMOkFihJnPntLYw1T0_NEMiHYSM0Q_u1JA&s=jDNnz34hmWvLSQnHkSnYdihW-jG-0xZ-YYqKq30wVGg&e=>
>>> >
>>> >
>>> >> A PR making the changes to the QUIC documents can be found at:
>>> >
>>> >> https://github.com/quicwg/base-drafts/pull/1377
>>> >
>>> >
>>> >> A few design details did not have clear consensus, but it was felt it
>>> > would be better to discuss those in the wider WG than delay the design
>>> > team.  A consistent choice was made in the PR and these issues are
>>> > mentioned in Appendix B of the design doc.
>>> >
>>> >
>>> >> As always, comments and questions welcome. That said, this is a big PR
>>> > and we recognize that some editorial work is going to be needed before
>>> > merging. In the interest of letting people follow along, and to keep
>>> github
>>> > from falling over, we ask people to keep discussion on the mailing
>>> list and
>>> > refrain from making PR comments.
>>> >
>>> >
>>> >> See you in Kista!
>>> >
>>> >
>>> >> Ian and Eric
>>> >
>>> >
>>>
>>>
>>>
>>> --
>>> Kazuho Oku
>>>
>>>
>>
>
>