Re: [quicwg/base-drafts] forbid key discarding before receiving a packet protected with new keys (#4079)

Martin Thomson <notifications@github.com> Wed, 09 September 2020 04:42 UTC

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Date: Tue, 08 Sep 2020 21:42:05 -0700
From: Martin Thomson <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] forbid key discarding before receiving a packet protected with new keys (#4079)
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@martinthomson commented on this pull request.



> @@ -1496,10 +1496,11 @@ The endpoint that initiates a key update also updates the keys that it uses for
 receiving packets.  These keys will be needed to process packets the peer sends
 after updating.
 
-An endpoint SHOULD retain old keys so that packets sent by its peer prior to
-receiving the key update can be processed.  Discarding old keys too early can
-cause delayed packets to be discarded.  Discarding packets will be interpreted
-as packet loss by the peer and could adversely affect performance.
+An endpoint MUST retain old keys until it has successfully unprotected a packet
+sent using the new keys.  An endpoint SHOULD NOT discard old keys immediately
+after unprotecting a packet sent using the new keys.  Discarding old keys too
+early can cause delayed packets to be discarded.  Discarding packets will be
+interpreted as packet loss by the peer and could adversely affect performance.

I think that it's OK to have two events, and technically the drop events are bound to use of keys.  In that regard, I'm comfortable with the text you have.  I don't think we need to rely exclusively on acknowledgments for driving this.

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