Re: [quicwg/base-drafts] Stateless reset comparisons (constant time/any order/datagram) (#2993)

ekr <> Wed, 16 October 2019 21:19 UTC

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Subject: Re: [quicwg/base-drafts] Stateless reset comparisons (constant time/any order/datagram) (#2993)
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ekr commented on this pull request.

> -If the last 16 bytes of the packet values are identical to a Stateless Reset
+An endpoint detects a potential stateless reset using the trailing 16 bytes of
+the UDP datagram.  An endpoint remembers all Stateless Reset Tokens associated
+with the connection IDs and remote addresses for datagrams it has recently sent.
+This includes Stateless Reset Tokens from NEW_CONNECTION_ID frames and the
+server's transport parameters but excludes Stateless Reset Tokens associated
+with connection IDs that are either unused or retired.  The endpoint identifies
+a received datagram as a stateless reset by comparing the last 16 bytes of the
+datagram with all Stateless Reset Tokens associated with the remote address on
+which the datagram was received.
+This comparison can be performed for every inbound datagram.  Endpoints MAY skip
+this check if any packet from a datagram is successfully processed.  However,
+the comparison MUST be performed when the first packet in an incoming datagram
+either cannot be associated with a connection, cannot be decrypted, or carries
+a duplicate packet number.

I don't think I understand the rationale for this duplicate packet number check. If you have a valid packet, it seems like one ought to assume that it's not also a stateless reset or coalesced with one.

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