Re: [quicwg/base-drafts] Authenticate connection IDs (#3499)

[David Schinazi <[e-mail]>]

@DavidSchinazi commented on this pull request.



> +~~~
+Client                                                  Server
+
+Initial: DCID=S1, SCID=C1 ->
+                                   <- Retry*: DCID=C1, SCID=S2
+Initial*: DCID=S2, SCID=C1 ->
+                                  <- Initial: DCID=C1, SCID=S3
+                             ...
+1-RTT: DCID=S3 ->
+                                             <- 1-RTT: DCID=C1
+~~~
+{: #fig-auth-cid title="Use of Connection IDs in a Handshake"}
+
+For the handshake in {{fig-auth-cid}} the client sets the value of the
+initial_source_connection_id transport parameter to `C1`. If the server sends a
+Retry packet (that is, the packets marked with a '*' are sent), it sets

I really like the diagram, but I would prefer to split it in two. There are two possible handshakes described here: without and with retry involved. I think that the `the packets marked with a '*' are sent` caveat is confusing, because when those packets aren't sent, the `1-RTT: DCID=S3` needs to be replaced by `1-RTT: DCID=S2`. It might be simpler to have two diagrams and two examples.

>  
 If the client received and processed a Retry packet, it MUST validate that the
-original_connection_id transport parameter is present and correct; otherwise, it
-MUST validate that the transport parameter is absent.  A client MUST treat a
-failed validation as a connection error of type TRANSPORT_PARAMETER_ERROR.
+retry_source_connection_id transport parameter is present and correct;
+otherwise, it MUST validate that the transport parameter is absent. A client
+MUST treat a failed validation as a connection error of type
+TRANSPORT_PARAMETER_ERROR.

This contradicts line 1568
> An endpoint MUST treat any of the following as a connection error of type PROTOCOL_VIOLATION

I have a slight preference for PROTOCOL_VIOLATION over TRANSPORT_PARAMETER_ERROR, though I don't much care as long as this section matches the other one.

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