[tor-dev] Hidden service policies

Mike Hearn mike at plan99.net
Tue Jul 22 12:42:53 UTC 2014

> Regardless of the moral arguments you put forward, which I will not
> comment on, it seems like this idea would never be implemented because
> none of the Tor developers have a desire to implement such a dangerous
> feature.

I can argue that the lack of it is also dangerous, actually. It amounts to
a form of "pick your poison".

Consider exit policies. Would Tor be better off if all relays were also
required to exit all traffic? I think it's obvious the answer is no because
there are currently ~5800 relays and ~1000 exits according to the lists
from torstatus.blutmagie.de, so most Tor relay operators choose not to
exit. If they didn't have that choice, there'd almost certainly be far
fewer relays. Allowing relays to contribute as much as they feel
comfortable with (or that their ISP feels comfortable with) helps the
project a lot.

Tor is not a large network. It's a niche product that routinely sacrifices
usability for better anonymity, and as a result is politically vulnerable.
I don't want Tor to be vulnerable, I think it's a useful piece of
infrastructure that will be critical for improving the surveillance
situation. Regardless, "anonymity loves company" and Tor has little. By
demanding everyone  who takes part support all uses of Tor simultaneously,
including the obviously bad ones, you ensure some people will decide not to
do so, reducing the company you have and thus making it easier for
politicians/regulators/others to target the network.

The above argument is general - it would also apply to giving end users
different tradeoffs in the TBB, for example, a mode designed for
pseudonymity rather than anonymity that doesn't clear cookies at the end of
the session. Then it'd be more convenient for users who don't mind if the
services they use can correlate data across their chosen username, they
just want a hidden IP address. Same logic applies - the more people use
Tor, the safer it is.

It may appear that because Tor has been around for some years and has not
encountered any real political resistance that it will always be like this.
 Unfortunately I don't think that's a safe assumption, at least not any
more. Strong end to end crypto apps that actually achieve viral growth and
large social impact are vanishingly rare. Skype was one example until they
got forced to undo it by introducing back doors. The Silk Road was another.
The combination of Bitcoin and Tor is very powerful. We see this not only
with black markets but also Cryptolocker, which appears to be the "perfect
crime" (there are no obvious fixes). So times have changed and the risk of
Tor coming to the attention of TPTB is much higher now.

The best fixes for this are:

   1. Allow people to explicitly take action against abuse of their own
   nodes, so they have a plausible answer when being visited individually.

   2. Grow usage and size as much/as fast as possible, to maximise
   democratic immunity. Uber is a case study of this strategy right now.

The absence of (1) means it'll be much more tempting for governments to
decide that all Tor users should be treated as a group.

> Further, why do you think such infrastructure would be remotely
> successful in stopping botnets from using the Tor network? A botnet
> could just generate a thousand hidden service keys and cycle through
> them.

That's a technique that's been used with regular DNS, and beaten before
(DGA). The bot gets reverse engineered to find the iteration function and
the domain names/keys eventually get sinkholed. There are counter measures
and counter-countermeasures, as always.

But yes, some types of abusers are harder to deal with than others, that's
for sure. If it helps, s/botnet/ransomware/. The same arguments apply. I
don't want to dwell on just botnet controllers.

With respect to your specific counter-arguments:

> So, this would be:
>       * Socially damaging, because it would fly in the face of Tor's
>         anti-censorship messaging

That seems like a risky argument to me - it's too easy for someone to flip
it around by pointing out all the extremely nasty and socially damaging
services that Tor currently protects. If you're going to talk about social
damage you need answers for why HS policies would be more damaging than
those things.

Also, the Tor home page doesn't prominently mention anti-censorship
anywhere, it talks about preserving privacy. If you wanted to build a
system that's primarily about resisting censorship of data it would look
more like Freenet than hidden services (which can be censored in a way
using DoS attacks and the like).

>       * Technically damaging, because it would enable the worst class of
>         attacks by allowing attackers to pick arbitrary introduction
>         points

Who are the attackers, in this case, and how do they force a selection of
introduction points? Let's say Snowden sets up a blog as a hidden service.
It appears in nobodies policies, because everyone agrees that this is a
website worth hiding.

If the attacker is the NSA, what do they do next?

>       * Not even technically helpful against other content, because they
>         can change addresses faster than volunteers maintaining lists of
>         all the CP onionsites can do the detective work (which you
>         assume people will want to do, and do rapidly enough that this
>         will be useful)

I didn't assume that, actually, I assumed that being able to set policies
over the use of their own bandwidth would encourage people to contribute
more - seems a safe assumption. You don't need perfection to achieve that

But regardless, changing an onion address is no different to changing a
website address. It's not sufficient just to change it. Your visitors have
to know what the new address is. You're an intelligent guy so I'm sure you
see why this matters.
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