> On 21 May 2019, at 00:35, George Kadianakis <desnac...@riseup.net> wrote:
>
> Tom Ritter <t...@ritter.vg> writes:
>
>>> On Thu, 16 May 2019 at 11:20, George Kadianakis <desnac...@riseup.net>
>>> wrote:
>>> 3) Duration of Activity ("DoA")
>>>
>>> The USENIX paper uses the period of time during which circuits send and
>>> receive cells to distinguish circuit types. For example, client-side
>>> introduction circuits are really short lived, wheras service-side
>>> introduction circuits are very long lived. OTOH, rendezvous circuits
>>> have
>>> the same median lifetime as general Tor circuits which is 10 minutes.
>>>
>>> We use WTF-PAD to destroy this feature of client-side introduction
>>> circuits by setting a special WTF-PAD option, which keeps the circuits
>>> open for 10 minutes completely mimicking the DoA of general Tor
>>> circuits.
>>
>> 10 minutes exactly; or a median of 10 minutes? Wouldn't 10 minutes
>> exactly be a near-perfect distinguisher? And if it's a median of 10
>> minutes, do we know if it follows a normal distribution/what is the
>> shape of the distribution to mimic?
>>
>
> Oops, you are right, Tom.
>
> It's not 10 minutes exactly. The right thing to say is that it's a median
> of 10 minutes, altho I'm not entirely sure of the exact distribution.
>
> These circuits basically now follow the MaxCircuitDirtiness
> configuration like general circuits, and it gets orchestrated by
> circuit_expire_old_circuits_clientside(). Not sure if it's in a spec
> somewhere.
>
> I will update the spec soon with the fix. Thanks!
If I understand correctly, Tor's circuits close about 10 minutes after
the last time they handled traffic.
So that's a *minimum* of 10 minutes. And probably a *median* of
slightly more than 10 minutes, if the user is web browsing.
T
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