[tor-talk] [tor-dev] high latency hidden services

[grarpamp]

On Tue, Dec 9, 2014 at 4:40 PM, Michael Rogers <michael at briarproject.org> wrote:
> On 25/11/14 12:45, George Kadianakis wrote:
>> Yes, integrating low-latency with high-latency anonymity is a very
>> interesting probleml. Unfortunately, I haven't had any time to
>> think about it.
>>
>> For people who want to think about it there is the "Blending
>> different latency traffic with alpha-mixing" paper. Roger mentioned
>> that one of the big challenges of making the paper usable with Tor,
>> is switching from the message-based approach to stream-based.
>>
>> Other potential papers are "Stop-and-Go-MIX" by Kesdogan et al.
>> and "Garbled Routing (GR): A generic framework towards unification
>> of anonymous communication systems" by Madani et al. But I haven't
>> looked into them at all...
>
> Two of these papers were also mentioned in the guardian-dev thread, so
> I guess we're thinking along similar lines.

> At least four characteristics can be used to match circuits entering
> and leaving a relay: start time, end time, total traffic volume and
> traffic timing. The design would need to provide ways to mix a circuit
> with other circuits with respect to each characteristic.

> Traffic volumes can also be mixed by discarding padding at each hop,

> There's currently no way to conceal traffic timing - each relay
> forwards cells as soon as it can.

Guilty of tldr here, yet similarly, with the easily trackable
characteristics firstly above, I'm not seeing a benefit to anything
other than filling all links with chaff which then hides all those
parameters but one...

Then as far as passive observation goes, you're left with only
packet clocking, for which you can use your bucket queueing randomizers
to defeat at no more than the cost of their average jitter width X
the number of hops.

http://en.wikipedia.org/wiki/Asynchronous_Transfer_Mode

Granted it does require a 'get what you pay for' dedicated pipe of
bandwidth [purchasing/giving] mentality, but at least among relays
that already exists today, and if that is returned by gaining more
resistance to GPA who can currently do something as simple as
counting bytes in a time and pumping your hidden services
while being their guard, well then, so what?

It's also conceivable that nodes could choose to carry a 'chaff
capable' flag. And that other nodes, and clients, could choose to
select and participate in that when building links.

Note, there's no change to the low-latency circuit based expectations
here at all, other than ability of CPU to process chaff operations.
Though that might be easier if using a UDP or packet switched model.

I'm sure someone has explored chaff in papers already. Is it valid?
As opposed to just requiring lots of new work to implement.

I can't see any other way to have both low latency and hide the
talkers other than filling bandwidth committed links with talkers.
And when you want to talk, just fill in your voice in place of the
fake ones you'd otherwise send. That seems good against the GPA
above.

The other question is how, similar to Sybil, does chaff hold up
when an ACTIVE adversary runs nodes and can therefore discriminate
wheat/chaff on those nodes and perhaps communicate that among
their nodes on the backend to reduce things back to being counting
bytes in time above. I'm thinking it's not any worse than today's Sybil
and/or untrusted nodes, and thus not a factor in considering
implementing chaff.