Re: [quicwg/base-drafts] Rules for discarding old keys (#1636)

[Martin Thomson <[e-mail]>]

martinthomson commented on this pull request.



> +handshake, as well as when keys are updated (see {{key-update}}).
+
+QUIC endpoints MUST retain keys until they are no longer needed.  If packets
+from a lower encryption level contain CRYPTO frames, frames that retransmit that
+data MUST be sent at the same encryption level.  Similarly, an endpoint
+generates acknowledgements for packets at the same encryption level as the
+packet being acknowledged.  Thus, it is possible that keys for a lower
+encryption level are needed for a short time after keys for a newer encryption
+level are available.
+
+An endpoint can only discard keys for a given encryption level only after it has
+both received and acknowledged all CRYPTO frames for that encryption level and
+when it has had all CRYPTO frames for that encryption level acknowledged by its
+peer.  However, this does not guarantee that no further packets will need to be
+received or sent at that encryption level because a peer might not have received
+all the acknowledgements necessary to reach the same state.

Yes, I think so.  The previous paragraph is intended to highlight the reasons why keys might be retained in a general sense.  The second paragraph is intended to be more precise about what the requirements are.  A small tweak to the lead-in of each should help emphasize the difference.

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