Re: [tor-dev] Evaluating rendezvous circuit build up CPU usage

[juanjo <juanjo@xxxxxxxxx>]

Hi, thanks for working on it.

At first I thought about using a PoW on the Introduction Point (I.P.) side.

Maybe a dynamic PoW? I mean only ask for PoW under load (Hidden services 
sets the INTRO1s/second on the I.P.) or ask for every new circuit.

Then I thought that we need to fix the Rendezvous verification issue 
too. We do not verify if the client/user/attacker actually opened a 
circuit to the Rend point. And I thought we could make the Rend sing a 
message and the I.P verify the signature before sending the INTRO2 to 
the HS.

But now I think we need to merge designs and make just one proposal 
fixing both problems at the same time.

If we don't want to make a PoW for every new circuit, we could make the 
client generate a private Identity (KeyPair) mixed with some sort of 
PoW, generating it for every HS a client want to connect. This way we 
only make PoW for each onion and the IP can have a replay cache (or 
something like that) with each identity and the last time it requested a 
new circuit. We can better control with this way the number of 
individual clients and we "save the planet" by not making a PoW for each 
new circuit. (Maybe this approach is what your are working at with the 
"token based approach").

Sorry for my english...


El 13/1/20 a las 13:39, Valentin Franck escribió:
> Hello tor-devs,
>
> I am currently working on a DoS mitigation system aiming to protect the
> availability of onion services flooded with INTRO2 cells. My idea is
> using a (Privacy Pass like) token based approach as suggested in
> https://trac.torproject.org/projects/tor/ticket/31223#comment:6
>
> For the evaluation of a first prototype I would like to compare CPU
> usage times at the onion service when a) launching a rendezvous circuit
> and b) validating a (potentially invalid) token. Is there an easy way,
> to measure the CPU time a service spends for all operations triggered
> when launching a new rendezvous circuit? Has somebody done that before?
> Basically, I want to measure how much CPU time we save, if we do not
> launch the rendezvous circuit. So far I have identified the following
> functions: launch_rendezvous_point_circuit() and
> service_rendezvous_circ_has_opened(). I understand that there is more
> operations involved for building new circuits, since circuits are built
> hop by hop. How can I  identify all relevant functions triggered after
> launching the rendezvous circuit and include them in my measurements?
>
> Once I have some reliable results I will provide you with more
> information on what I am doing and how it is working so far.
>
> Cheers
> Valentin
>
> This is my first post on this list :-). So have mercy, if I overlooked
> resources to answer my question. Also, I am only beginning to
> familiarize myself with the existing code base.
>
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