[tor-dev] Relay "Ping" Functionality

[grarpamp]

> 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.

Use OnionCat and ping6, it is exactly what you want.

https://www.onioncat.org/

Such "timing" attacks are in the scope of "Tor Stinks  -- NSA"
document. Users should become familiar with them, and that
slide deck, and other attacks from over a decade ago.
And with how tor does not address them.