cloudflare
Allow to specify dcid when creating a client side connection
Motivation:
Sometimes the user want to have control over generating the dcid when creating a new client side connection. This was not possible before.
Modification:
- Only use dcid for local transport params when the connection is for server side
- Use provided odcid as dcid on the client side when given and if not just randomly generate one
Result:
More flexible usage possible
I really only care about be able to do this using the c headers but never less thought it might also be useful to be able to do this via the rust api so I added two new functions there as well.
The RFC places requirements for unpredictability and length on the client DCID field; see https://datatracker.ietf.org/doc/html/rfc9000#section-7.2-3
I'm concerned this change can make QUIC connections vulnerable, in ways described in the RFC security considerations, or in ways that are yet to be determined.
That said, there could be use cases where a deterministic CID (yet unpredictable to some actors) is useful.
Providing safety rails for the majority of default users is important. Perhaps this could be placed behind a very explicit opt-in feature flag with some clear warning are references to the relevant RFC text
The RFC places requirements for unpredictability and length on the client DCID field; see https://datatracker.ietf.org/doc/html/rfc9000#section-7.2-3
I'm concerned this change can make QUIC connections vulnerable, in ways described in the RFC security considerations, or in ways that are yet to be determined.
Fair enough...
That said, there could be use cases where a deterministic CID (yet unpredictable to some actors) is useful.
Yeah that's why I need it :)
Providing safety rails for the majority of default users is important. Perhaps this could be placed behind a very explicit opt-in feature flag with some clear warning are references to the relevant RFC text
That would be fine with me ... That said I think we could also add some validations for the length at least (must be at least 8 bytes). Let me do this in any case.
@LPardue added the length check and also added some more docs. That said I would also be ok to just remove the two new rust functions completely as long as I can do it via FFI / c :)
Just to make it clear.... I basically (as a library user) would like to be able to control how this random value is generated for the DCID.
As noted in https://github.com/cloudflare/quiche/pull/2234#issuecomment-3495528844, I think this need to be put behind a feature flag. I'm not willing to make this the default behaviour and risk clients accidentally using the API incorrectly