Re: [quicwg/base-drafts] Disallow reuse of stateless reset tokens (#2785)

[Kazuho Oku <[e-mail]>]

> Apologies for not raising this on #2732, I had not thought about the problem at that time.

It's my understanding that #2769 _is_ introducing this issue. There is no problem in the current design, because receiving a packet with an outdated CID is not expected to cause a stateless reset.

Regarding why you'd want to reuse a SRT, the simple reason is because you do not need to create different SRTs for every Connection ID.

A QUIC stack that generates a CID by a construction like `AES_ECB(cid_key, conn_id || path_index)`<sup>1</sup> can use `HMAC(srt_key, conn_id)` as a construction for generating SRT. 

For QUIC stacks that aren't interested in retiring CIDs (which seems to be the majority for me), this construction makes sense. I think my preference would be to retain the design; it's just about adding a warning when you want to retire a CID.

1: path_index is a sequence number of path for each connection

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