Stream0 Proposal: CRYPTO_HS frame encoding (Re: Stream0 Design Team Proposal)

[Kazuho Oku <[e-mail]>]

2018-05-24 8:51 GMT+09:00 Martin Thomson <[e-mail]>:
> I'm not a fan of micro-optimizations like this, especially when it means
> taking space we don't need.
>
> We don't need ANY of the bits on the CRYPTO stream.  The savings for an
> absent length and offset are marginal and not worth burning 8 frame types
> on, and the stream never really ends.  So if we made it have a type of
> 0x18, then you would run it through the same code and get the same result.

Clarification question: are you and EKR suggesting something like below?

0x10 - 0x17: STREAM frame
0x18: CRYPTO_HS frame

if (0x10 <= type && type <= 0x18)  {  // STREAM or CRYPTO_HS frame
     if (type != 0x18) streamID = varint_consume(frame);
     if ((type & 0x04) || type == 0x18) offset = varint_consume(frame);
     if ((type & 0x02) || type == 0x18) length = varint_consume(frame);
     if (type & 0x01) fin = 1;
     read body if present
}

I think that is workable, although it makes me sad because we will
have more conditional branches.

> On Wed, May 23, 2018 at 4:40 PM Jana Iyengar <[e-mail]> wrote:
>
>> Thank you for your implementation and your report -- this is terrific and
> helpful!
>
>> On your note about CRYPTO_HS frames, I think your idea is clever. Just to
> ensure that I am understanding it correctly, I believe you're proposing
> defining:
>> 0x10 - 0x17: STREAM frame
>> 0x18 - 0x1F: CRYPTO_HS frame
>
>> We can the same frame format for CRYPTO_HS as STREAM except that
> CRYPTO_HS will not have the stream ID field. This means an implementation
> handling these frames can reuse the stream machinery with a small change to
> parse the header bits as follows:
>
>> if (type & 0x10)  {  // STREAM or CRYPTO_HS frame
>>      if (type & 0x08) streamID = varint_consume(frame);
>>      if (type & 0x04) offset = varint_consume(frame);
>>      if (type & 0x02) length = varint_consume(frame);
>>      if (type & 0x01) fin = 1;
>>      read body if present
>> }
>
>> On Tue, May 22, 2018 at 9:57 PM, Kazuho Oku <[e-mail]> wrote:
>
>>> FWIW, I am happy to tell you that I have a working PoC code for the
>>> proposed approach.
>
>>> On the QUIC side, I saw 2% (124 lines) increase in code size (more on
>>> that below). On the TLS side, I also saw 2% (175 lines) increase.
>>> However please look at the code size change especially on the QUIC
>>> side with grain of salt, as it is just a PoC.
>
>>> As expected, the key and encryption-level management on the QUIC side
>>> became very clean. Following are some of the design decisions I made
>>> as well as the outcomes:
>
>>> * All the interaction between picotls and quicly are accompanied by
>>> "epoch". Handshake messages are attributed with their epochs so that
>>> they do not get protected by the wrong key, or so that octets received
>>> under an incorrect encryption context cannot be misused.
>
>>> * All the traffic keys are governed by quicly (managing some traffic
>>> keys in TLS while managing PNE key in QUIC seems messy).
>
>>> * The Initial key is setup by quicly, wheeras other traffic keys are
>>> installed by picotls by calling a callback named
>>> update_traffic_key_cb. The callback accepts and installs 6 keys in
>>> total: for three levels (i.e. 0-RTT, handshake, 1-RTT) in two
>>> directions (send-side and receive-side).
>
>>> * Three PN spaces have their own AEAD encryption key. Initial PN and
>>> Handshake PN spaces have one aead decryption key each. Application PN
>>> space has up to two decryption keys: either for 0-RTT and 1-RTT or for
>>> two 1-RTT keys during key update.
>
>>> It was a pain to have a dedicated frame encoding for CRYPTO_HS, even
>>> though we can reuse (and I reused) the retransmission and reassembly
>>> logic of QUIC streams for the handshake flows. About a half of the
>>> code size increase comes from that (the other half comes from the
>>> added abstraction for having two contexts for the handshake). I would
>>> prefer reusing the STREAM frame encoding for the handshake data. We
>>> could possibly use a different base offset (i.e. for CRYPTO_HS frames
>>> we could use 0b00011XXX, whereas the STREAM frames use 0b00010XXX), as
>>> well as omitting the Stream ID field.
>
>>> Overall, now that I have a PoC, I am more confident that the proposed
>>> approach is the correct path forward. It *simplifies* the QUIC stack
>>> at the same time giving us better security properties as well as
>>> fixing various issues in the current design (as discussed in the
>>> design doc).
>
>
>>> 2018-05-23 10:30 GMT+09:00 Ian Swett <ianswett=
> [e-mail]>:
>>> > 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://docs.google.com/document/d/1fRsJqPinJl8N3b-bflDRV6auojfJLkxddT93j6SwHY8/edit
>>> >
>>> >
>>> > 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



-- 
Kazuho Oku