Re: [tor-dev] Proposal xxx: Filtering malicious rendezvous points at hidden service server side

On 25 Jan 2016, at 03:10, s7r <s7r@xxxxxxxxxx> wrote:

Signed PGP part
Hi teor,

On 1/24/2016 6:33 AM, Tim Wilson-Brown - teor wrote:
> Please read the tor man page documentation for the option
> Tor2webRendezvousPoints. It's implemented in the function
> pick_tor2web_rendezvous_node().
>
> Under this proposal, what is the smallest number of rendezvous
> points a Tor2web instance would need to specify in
> Tor2webRendezvousPoints to avoid being banned, or does it vary
> depending on the popularity of the hidden service?
>

Ideally pick_tor2web_rendezvous_node() should pick a random relay to
act as a rendezvous point, based on its consensus weight / middle
probability fraction, exactly the same as any regular client would do.

This isn't how the current Tor2web implementation works. If your proposal will

break the Tor2webRendezvousPoints option, or require a minimum number of

relays to be specified in that option, you need to document these implementation

changes or new configuration constraints clearly in the proposal.

...
For load balancing and capacity and everything, a tor2web service
should always choose a random rendezvous relay for every circuit, and
ideally (don't know if it's possible in reverse proxy mode) re-use the
same circuit to the same hidden service if there are multiple visitors
(tor2web clients) asking to connect to the same hidden service.

I'm not sure whether different Tor2web web clients get different hidden service

circuits. But as it's critical to the correct functioning of this proposal with Tor2web

mode, I'd encourage you to find out, and update the proposal accordingly.

If
this is not possible (using one circuit per hidden service
destination, regardless if there are more people accessing that hidden
service address via tor2web) at least it should pick randomly
rendezvous relays for every circuit.

This isn't how Tor2web mode works. If your proposal needs the design to be

changed, then please document that.

This way, no rendezvous nodes will be banned. And the number of
rendezvous circuits we allow with a single relay as rendezvous point
is of course dependent on the popularity of the hidden service (total
number of rendezvous circuits built by that hidden service in the last
24 hours). So if a hidden service experienced 10000 rendezvous
circuits in the last 24 hours, a relay with middle probability
fraction of 0.5% is able to build at least 10000 * 0.005 = 50 new
rendezvous circuits before might get banned for the next 24 hours by
that hidden service.

So the number of rendezvous points required in Tor2webRendezvousPoints

depends on the load on the particular hidden service, the number of web

clients connecting to the particular hidden service via the Tor2web instance,

and whether those clients get the same rendezvous circuit or not.

Such a non-deterministic requirement essentially breaks the

Tor2webRendezvousPoints feature.

P.S. Picking the same rendezvous relays in tor2web services sounds
like we are hammering them too much.