[tor-onions] Probably-stupid question about Circuit IDs

[Dave Rolek]

On 2018-09-22 06:29, Alec Muffett wrote:
> ...and it makes me wonder how far back up the chain of hops towards
> the client, that the circuit ID is visible to a malicious relay? Is it
> mostly-hidden several onion-skins down? I presume it's not trackable
> all the way from the client's guard?

Hey Alec!

The circID is scoped under a given connection between adjacent nodes.

A relay node maintains a mapping of circIDs for a circuit - mapping the
forward and backward circID - for traffic it is relaying.

So for a circuit ...
   client <-ID_a-> guard <-ID_b-> middle <-ID_c-> exit

... each of the ID_*s are independent, and any node only knows the IDs
immediately "adjacent" to it. Each connection (e.g. each client to that
guard) has a independent enumeration/allocation of IDs.

Hope that helps!
Dave