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

[Jana Iyengar <[e-mail]>]

@janaiyengar requested changes on this pull request.

A few comments. Most importantly, mention of ODCID field needs to be removed.

> +{{transport-parameters}}. This ensures that all connection IDs are authenticated
+by the cryptographic handshake.

```suggestion
{{transport-parameters}}. This ensures that all connection IDs used for the
handshake are also authenticated by the cryptographic handshake.
```

> +(original_connection_id, preferred_address, retry_connection_id, and
+stateless_reset_token). A server MUST treat receipt of any of these transport

```suggestion
original_connection_id, preferred_address, retry_connection_id, or
stateless_reset_token. A server MUST treat receipt of any of these transport
```

> @@ -4794,9 +4854,9 @@ immediately after opening.  If the transport parameter is absent, streams of
 that type start with a flow control limit of 0.
 
 A client MUST NOT include server-only transport parameters

```suggestion
A client MUST NOT include any server-only transport parameter:
```

> @@ -1475,6 +1475,49 @@ lifetime of a connection, especially in response to connection migration
 ({{migration}}); see {{issue-cid}} for details.
 
 
+## Authenticating Connection IDs {#cid-auth}
+
+The choice each endpoint makes about connection IDs during the handshake is
+authenticated by including all values in transport parameters; see
+{{transport-parameters}}. This ensures that all connection IDs are authenticated
+by the cryptographic handshake.
+
+Each endpoint includes the value of the Source Connection ID field from Initial
+packets it sends in the handshake_connection_id transport parameter; see
+{{transport-parameter-definitions}}. A server includes the Destination
+Connection ID field it receives in the original Initial packet from the client

```suggestion
Connection ID field it receives in original Initial packets from the client
- Initial packets received by the server prior to sending a Retry packet -
```

> +Each endpoint ensures that the values of the peer's transport parameters
+match the values the endpoint sent in its packet headers. The values

```suggestion
The values
```
This first sentence is unnecessary.

> +values that an endpoint used in the Destination Connection ID field of an
+Initial packet. Including connection ID values in transport parameters and

```suggestion
values that an endpoint used in the Destination Connection ID field of Initial
packets that it sent. Including connection ID values in transport parameters and
```

> +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:

```suggestion
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:
```

> +{{transport-parameter-definitions}}.  If the server sends a Retry packet, the
+server adds a retry_connection_id transport parameter that contains the value of
+the Source Connection ID field from the Retry packet.

```suggestion
{{transport-parameter-definitions}}.  If it sends a Retry packet, the server
also subsequently includes the value of the Source Connection ID field from
the Retry packet in its retry_connection_id transport parameter.
```

> +A server always includes an original_connection_id transport parameter. If the
+server sends a Retry packet, it MUST include the Destination Connection ID field
+from the client's first Initial packet in the original_connection_id transport
+parameter; otherwise the original_connection_id transport parameter MUST be
+copied from the client Initial.

```suggestion
A server always includes an original_connection_id transport parameter. If it
sends a Retry packet, the server MUST subsequently include the Destination
Connection ID field from the client's original Initial packets - packets received
by the server prior to sending the Retry packet -  in the original_connection_id
transport parameter. If the server did not send a Retry packet, the value of the
original_connection_id transport parameter MUST be copied from the
Destination Connection ID field of the most recent client Initial packets.
```

> +  by a server.  This is the same value sent in the Original Destination
+  Connection ID field that is used to construct a Retry packet (see
+  {{packet-retry}}).

```suggestion
  by a server.  The value of this parameter depends on whether the server
  sent a Retry packet (see {{packet-retry}}).
```

> @@ -1475,6 +1475,48 @@ lifetime of a connection, especially in response to connection migration
 ({{migration}}); see {{issue-cid}} for details.
 
 
+## Authenticating Connection IDs {#cid-auth}
+
+The choice each endpoint makes about connection IDs during the handshake is
+authenticated by including all values in transport parameters; see
+{{transport-parameters}}. This ensures that all connection IDs are authenticated
+by the cryptographic handshake.
+
+Each endpoint includes the value of the Source Connection ID field from Initial
+packets it sends in the handshake_connection_id transport parameter; see

In keeping with retry_connection_id being the SCID that is used on Retry packets, I have a preference for initial_connection_id, since it is the SCID used on Initial packets. 

In the same vein, and this is a weaker preference, I would propose changing original_connection_id to original_initial_connection_id. I think this makes it clear that this might have been initial_connection_id had it not been for a Retry.

> +Each endpoint includes the value of the Source Connection ID field from Initial
+packets it sends in the handshake_connection_id transport parameter; see

```suggestion
Each endpoint includes the value of the Source Connection ID field from the 
most recent Initial packet it sent in the handshake_connection_id transport
parameter; see
```

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