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

[David Schinazi <[e-mail]>]

DavidSchinazi approved this pull request.

Thanks for writing this! I support this change and only have minor nits.

> +verifying them ensures that the choice of connection ID cannot be influenced by
+an attacker. An endpoint MUST treat any of the following as a connection error
+of type PROTOCOL_VIOLATION:
+
+* absence of the handshake_connection_id transport parameter from either
+  endpoint,
+
+* absence of the original_connection_id transport parameter from the server,
+
+* absence of the retry_connection_id transport parameter from the server after
+  receiving a Retry packet,
+
+* presence of the retry_connection_id transport parameter when no Retry packet
+  was received, or
+
+* a mismatch between values of these transport parameters and the Destination

I think you mean `a mismatch between values of these transport parameters and the respective Connection ID fields an endpoint used.` since it doesn't just protect destination

> @@ -1522,9 +1560,10 @@ specify whether they MUST, MAY, or MUST NOT be stored for 0-RTT. A client need
 not store a transport parameter it cannot process.
 
 A client MUST NOT use remembered values for the following parameters:
-original_connection_id, preferred_address, stateless_reset_token, and
-ack_delay_exponent. The client MUST use the server's new values in the
-handshake instead, and absent new values from the server, the default value.
+ack_delay_exponent, handshake_connection_id, original_connection_id,

Shouldn't `original_connection_id` stay in this list? And what about `handshake_connection_id`?

> @@ -4357,13 +4395,15 @@ A client MUST NOT reset the packet number for any packet number space after
 processing a Retry packet; {{packet-0rtt}} contains more information on this.
 
 A server acknowledges the use of a Retry packet for a connection using the
-original_connection_id transport parameter (see
-{{transport-parameter-definitions}}).  If the server sends a Retry packet, it
+retry_connection_id transport parameter; see
+{{transport-parameter-definitions}}. If the server sends a Retry packet, it

We may want to rephrase this to more clearly state that `original_connection_id` is always filled in by the server

> @@ -4572,9 +4612,8 @@ original_connection_id (0x00):
 
 : The value of the Destination Connection ID field from the first Initial packet
   sent by the client.  This transport parameter is only sent by a server.  This
-  is the same value sent in the "Original Destination Connection ID" field of a
-  Retry packet (see {{packet-retry}}).  A server MUST include the
-  original_connection_id transport parameter if it sent a Retry packet.
+  is the same value sent in the "Original Destination Connection ID" field that

Thanks for catching that, my bad for missing it.

> @@ -4742,6 +4781,22 @@ active_connection_id_limit (0x0e):
   When a zero-length connection ID is being used, the active_connection_id_limit
   parameter MUST NOT be sent.
 
+handshake_connection_id (0x0f):
+
+: The value that the endpoint included in the Source Connection ID field of the
+  first Initial packet it sends during the handshake. Endpoints MUST validate
+  that this transport parameter is present and that it matches the value that
+  was received in Initial packets. Authenticating this value ensures that an
+  attacker is unable to influence the selection of connection IDs during the

to avoid jinxing things, how about `Authenticating this value mitigates an attacker's ability to influence the selection of connection IDs during the handshake.`

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