Re: [quicwg/base-drafts] Remove handshake confirmed test for KeyUpdate (#3212)

Kazuho Oku <notifications@github.com> Thu, 28 November 2019 02:14 UTC

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Date: Wed, 27 Nov 2019 18:13:59 -0800
From: Kazuho Oku <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] Remove handshake confirmed test for KeyUpdate (#3212)
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@martinthomson 
> As long as we are OK with that outcome, I don't think that this needs to change (@kazuho certainly argued for some way to hold the first key update back, which I think was derived from not wanting too many keys active at the same time).

+1 to not changing status quo.

My argument was that there should be a gap between when an endpoint starts using 1-RTT keys and when it issues the first key update, based on the agreement is that the minimum number of keys that a endpoint is required to possess should be 2.

Unlike Initial or Handshake keys, 0-RTT key does not have a defined moment when it is to be discarded. Instead, it is discarded some time after exchange happens using the first set of 1-RTT keys, which IMO is exactly the same as how key update retires an old set of 1-RTT keys.

Based on this view, it is natural to hold two set of application traffic keys (regardless of the key being 0-RTT or 1-RTT), rotating them as necessary. As we have discussed and agreed, there needs to be a gap between each installation event of a new traffic key.

In status quo, the minimum gap between the use of the first 1-RTT key and the use of the second 1-RTT key is 1-RTT. The recommended gap between the following key update events are 3 PTO. Even though the size of the gaps are different, they both serve as a window at which the old key (could be either 0-RTT key or 1-RTT key) can coexist. This is fine.

My argument was that _if_ we are to change the requirement, it would make sense to consider aligning the size of the recommended gap between the use of 1-RTT key and the use of the second 1-RTT key to 3 PTO.

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