Stream0 Proposal: Explicit vs. Implicit ACK (Re: Stream0 Design Team Proposal)

[Kazuho Oku <[e-mail]>]

2018-05-24 3:46 GMT+09:00 Jana Iyengar <[e-mail]>:

> A thought occurs to me: a CRYPTO_HS frame with the fin bit set can be used
> to indicate that the handshake is done.This could be used as a signal (aka
> HANDSHAKE_DONE) to solve Marten's problem of a client rtxing a CFIN. Of
> course, this would mean that this particular CRYPTO_HS frame would be
> encrypted with a 1-RTT key... which *I think* is fine. What do you think?

I am not sure if that is a good approach.

I would assume that we would like to keep the handshake flow on the
1-RTT key open for the lifetime of the QUIC connection, so that we
could send things related to the TLS (e.g. session tickets). Sending
FIN from the server right after receiving ClientFinished makes that
impossible.

Having said that, I do agree that the need for a dedicated frame is a
pain. It is a pain because we need to have a retransmission logic for
the frame.

I think that you are making a good point in suggesting to consider
reusing the retransmission logic that already exists for bidirectional
flows. But as said, FIN bit does not seem like an answer in this case.

IMO, ideally we should define a new TLS post-handshake message (that
does not convey any data), and send that from the server in response
to ClientFinished using 1-RTT packet. The message will act as a signal
that the server has received ClientFinished.

The benefit of this approach is that we can reuse the retransmission
logic that will exist for handshake flows. The downside is that TLS
stacks need to be aware of the new handshake message.

Considering the fact that the Design Team is already suggesting a
substantial change to the TLS stack, we might have chance in asking
for the addition of a new handshake message. But I am not sure.

-- 
Kazuho Oku