Re: [quicwg/base-drafts] RESET_STREAM should be allowed in 0-RTT packets (#2344)

Kazuho Oku <> Tue, 22 January 2019 01:46 UTC

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From: Kazuho Oku <>
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Subject: Re: [quicwg/base-drafts] RESET_STREAM should be allowed in 0-RTT packets (#2344)
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>> The problem with 0-RTT in QUIC is that, unlike TLS 1.3 (that has max_early_data_size), there is no limit in the amount of data that the client can send using the 0-RTT key. IIUC, currently, it's entirely up to the client to decide when it switches from 0-RTT to 1-RTT keys.
> QUIC uses `initial_max_data` for that purpose. You can't receive a flow control update, so whatever value you have for that determines how much 0-RTT you can send.

My understanding is that an attacker acting as a client _can_ receive flow control updates (in 1-RTT packets), and use the updated value for emitting additional 0-RTT packets. Something like following:
* client obtains to a server and obtains session ticket and TP
* client reconnects, sends 0-RTT packets containing a STREAM frame (id=0, off=TP.initial_max_data-1, len=1)
* server sends handshake messages and a 1-RTT packet that contains MAX_DATA (maximum_data=TP.inital_max_data*3), because it observes the client reaching the limit
* client sends a _0-RTT_ packet containing a STREAM frame (id=0, off=TP.initial_max_data*3-1, len=1)
* server sends another 1-RTT packet containing MAX_DATA...
* client sends a _0-RTT_ packet containing a yet another STREAM frame...

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