[tor-dev] Reporting Relay Bandwidth Less Often

[teor]

Hi all,

We would like to make Tor relays report their bandwidth statistics
every 24 hours, rather than every 4 hours. We believe that this is a
safer interval for clients. It makes it harder to discover the guards of
clients that use a lot of bandwidth, particularly onion services.

Here's how this kind of guard discovery can happen:
* a client repeatedly downloads a large file, or an onion service
  becomes very popular, or is repeatedly asked for a large file
* the traffic statistics for the client's guard increase dramatically
  in the next 4 hours
* an adversary watches the traffic statistics across the whole network,
  and finds the ones with dramatic increases

Increasing the bandwidth statistics interval slows down this attack:
* it requires more bandwidth to produce a 24 hour spike
* each statistics interval is longer, so it takes more time to be sure
  of the guard

One of the impacts of this change is that relay bandwidth graphs are
less detailed. We will encourage relay operators to view detailed
graphs using local tools like Nyx or Munin or similar, because this is
safer for clients.

We are tracking this work in this trac ticket:

https://trac.torproject.org/projects/tor/ticket/23856

Tim

--
Tim / teor

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