Re: [quicwg/base-drafts] Rework Retry packet (#1498)

[Martin Thomson <[e-mail]>]

martinthomson commented on this pull request.



> +
+A Retry packet does not include a packet number and cannot be explictly
+acknowledged by a client.
+
+A server MUST only send a Retry in response to a client Initial packet.
+
+If the Original Destination Connection ID field does not match the Destination
+Connection ID from most recent the Initial packet it sent, clients MUST discard
+the packet.  This prevents an off-path attacker from injecting a Retry packet
+with a bogus new Source Connection ID.
+
+The client responds to a Retry packet with Initial packet that includes the
+provided Retry Token to continue connection establishment.
+
+A server that might send another Retry packet in response to a subsequent
+Initial packet MUST set the Source Connection ID to new value of at least 8

If things on the path aren't planning to terminate the connection (presumably they know this), then they can never send a token with <8.

8 is the number we picked for Initial.  It seemed best to align with that.  That's all.  It's probably the case that 4 would give us equivalent defense against off-path attacks to the TCP handshake, but there is value in consistency here.

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