[tor-relays] Circuit ID assignment

[teor]

Hi,

For those reading along, this conversation started on tor-onions:
https://lists.torproject.org/pipermail/tor-onions/2018-September/date.html

> On 10 Oct 2018, at 08:24, nusenu <nusenu-lists at riseup.net> wrote:
> 
> Gabbi Fisher:
>> 
>> 
>> I wanted to learn more about how Tor circuit IDs work. Correct me if I'm
>> wrong, but this is my current understanding:
>> 
>> Each hop along the Tor network has its own circuit ID number. (No universal
>> circuit ID number is used to identify a ip-to-ip stream of traffic). How
>> are the circuit ID numbers determined at each hop?

Circuit IDs are generated at random, with range restrictions depending on the
negotiated link protocol version. See the spec for details.

>> What generates the
>> circuit ID number given to a packet?

The initiating client or relay includes a random ID in the CREATE cell.
Subsequent cells in both directions on that circuit are given the same ID.

> maybe the tor-spec can help here:
> https://gitweb.torproject.org/torspec.git/tree/tor-spec.txt#n937
> 
> if it doesn't, the tor-dev ML might be a better place.

+1

T