Re: [quicwg/base-drafts] describe how 0-RTT is accepted and rejected (#2841)

[Kazuho Oku <[e-mail]>]

kazuho commented on this pull request.



>  
-A server rejects 0-RTT by rejecting 0-RTT at the TLS layer.  This also prevents
-QUIC from sending 0-RTT data. A server will always reject 0-RTT if it sends a
-TLS HelloRetryRequest.
+A server rejects 0-RTT by sending a ServerHello without the EarlyDataIndication.
+A server will always reject 0-RTT if it sends a TLS HelloRetryRequest.  When
+rejecting 0-RTT, a server MUST NOT process any 0-RTT packets, even if it is in
+possesion of the keys to do so.  When 0-RTT was rejected, a client MUST treat
+receipt of an acknowledgement for a 0-RTT packet as a connection error of type

@martinthomson I disagree that is is easy to detect.

It is true that it is easy for a QUIC stack that uses different packet number spaces to detect this error. This is because all you need to do is remember the largest PN used for the 0-RTT packet, and compare that with ACKs you receive in the application space.

OTOH, this is difficult for a QUIC stack that uses unified packet number space. Such stacks would be required to remember all the PNs being used for sending 0-RTT packets.

The other question is if we need to require endpoints to posses the 0-RTT keys, even after it detects that 0-RTT has been rejected. Unless we require that, having this MUST becomes much useless.

Speaking of text, I think there are four options:
a) MUST detect and close
b) SHOULD detect and close
c) MUST close if detected
d) SHOULD close if detected

As stated, I oppose to _a_ because it could be hard to detect. I think _c_ is fine. I might agree that _b_, _d_ might not be good, though I wonder what's the necessity to have something different from the general rule of handling ACKs carrying invalid PNs. Maybe the general rule needs to be changed to MUST.

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