Re: [quicwg/base-drafts] Flow control for post-handshake CRYPTO messages (#1834)

Kazuho Oku <> Fri, 26 October 2018 02:02 UTC

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From: Kazuho Oku <>
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Subject: Re: [quicwg/base-drafts] Flow control for post-handshake CRYPTO messages (#1834)
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>> I had assumed that TLS stacks always expose the 1-RTT read key to the QUIC stacks acting as a server when it receives ClientFinished. I'd be curious to know if there are TLS stacks that takes an alternative approach.
> That was what I had assumed too, until I thought through the nasty interactions with partial Handshake flights and 0-RTT. That is, the TLS stack makes secrets available at the point that it would normally be installing them for its own use. In that way, a server wouldn't install the 1-RTT read keys until it had processed the finished from the client, exactly as you say.

Thank you for pointing that out. I forgot about that exception. So while that is the only exception picotls has in terms of key installation timing, I agree that it's merely about having one exception or two...

> But it also smells weird, so perhaps proper flow control (toss post-hs stuff onto stream 0?) would be better instead?

I am totally fine with handwaving, but in case we are to have flow control, I'd prefer having flow control for CRYPTO streams in all epochs. They could all use a fixed-size window that would be defined in the specification. I prefer that because IMO having flow control for every stream (i.e. all the ordinary streams + all the 4 CRYPTO streams) is a simplification.

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