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

[Marten Seemann <[e-mail]>]

@marten-seemann commented on this pull request.



> +first Initial packet it sent in the initial_source_connection_id transport
+parameter; see {{transport-parameter-definitions}}. A server includes the
+Destination Connection ID field from the first Initial packet it received from
+the client in the original_destination_connection_id transport parameter; if
+the server sent a Retry packet this refers to the first Initial packet received
+before sending the Retry packet. If it sends a Retry packet, a server also
+includes the Source Connection ID field from the Retry packet in the
+retry_source_connection_id transport parameter.
+
+The values provided by a peer for these transport parameters MUST match the
+values that an endpoint used in the Destination and Source Connection ID fields
+of Initial packets that it sent. Including connection ID values in transport
+parameters and verifying them ensures that that an attacker cannot influence
+the choice of connection ID for a successful connection by injecting packets
+carrying attacker-chosen connection IDs during the handshake. An endpoint MUST
+treat any of the following as a connection error of type PROTOCOL_VIOLATION:

Our rule for FRAME_ENCODING_ERROR is that we use that error code when the error is detectable while parsing the frame, without accessing connection state. I'd argue that we should apply a similar logic here. The absence of `initial_source_connection_id` and `original_destination_connection_id` definitely falls in that category, and I'd put the absence / presence of `retry_source_connection_id` in the same category, although I could see why someone could make an argument against this.

The mismatch seems to be a clear case for PROTOCOL_VIOLATION.

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