[tor-dev] Relay "Ping" Functionality

[r.a at posteo.net]

Hey,

On 21.01.22 14:57, Alexander Mages wrote:
> Right now we're exploring latency-based attacks but are having trouble 
> achieving a particular goal: a way to “ping” an arbitrary node in a 
> client’s already-built (“live”) circuit. One-way timing is ideal but 
> round trip time would suffice. We can glean this information during 
> circuit construction, but what about a “live” circuit? Ideally, this 
> would be a periodic thing Tor already keeps track of, but as an 
> on-demand or as a byproduct/side-effect of a different function would 
> also work. We have not been able to find a way to do this within the Tor 
> (sub)protocol specs or the control port spec.


You can measure the RTT between your client and a node by exiting 
through that node and intentionally violating its exit policy, such as 
connecting to 127.0.0.1:80. The node will return an error, and you can 
measure the RTT as the time between sending the request and receiving 
the error. See https://naviga-tor.github.io/ for an example.


All the best,
Robert