Re: [quicwg/base-drafts] Rewrite key update section (#3050)

[David Schinazi <[e-mail]>]

DavidSchinazi commented on this pull request.



> +
+## Timing of Receive Key Generation {#receive-key-generation}
+
+Endpoints responding to an apparent key update MUST NOT generate a timing
+side-channel signal that might indicate that the Key Phase bit was invalid (see
+{{header-protect-analysis}}).  Endpoints can use dummy packet protection keys in
+place of discarded keys when key updates are not permitted; using dummy keys
+will generate no variation in the timing signal produced by attempting to remove
+packet protection, but all packets with an invalid Key Phase bit will be
+rejected.
+
+The process of creating new packet protection keys for receiving packets could
+reveal that a key update has occurred.  An endpoint MAY perform this process as
+part of packet processing, but this creates a timing signal that can be used by
+an attacker to learn when key updates happen and thus the value of the Key Phase
+bit in certain packets.  Endpoints SHOULD instead defer the creation of the next

Ah, that makes a lot more sense. Thanks.

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