[tor-dev] Does a design document for the DoS subsystem exist?

[Lennart Oldenburg]

Hello George, hello all,

Thank you very much for the provided pointers. Great to hear progress is
being made on the Onion Services DoS matter. Two follow-up questions:

1) Will the DoS subsystem overhaul also affect guard-centric DoS
countermeasures? Or will it exclusively focus on DoS protection specific
to Onion Services? If guard-centric countermeasures are also being
updated, is there a document to see what is about to change?

2) The linked bug ticket [1] under your first bullet point does not
mention the origin of the concrete threshold values
(DoSCircuitCreationRate, etc.). Could you share any insight on how these
DoS threshold values are determined? Are they inferred from experiments?

Thank you.

Kind regards
Lennart Oldenburg

[1] https://trac.torproject.org/projects/tor/ticket/24902

On 13/04/2020 23.50, George Kadianakis wrote:
> Lennart Oldenburg <lennart.oldenburg at esat.kuleuven.be> writes:
> 
>> Hi all,
>>
>> We are investigating how Tor protects itself against Denial-of-Service
>> (DoS) attacks. So far, it has been difficult to find a comprehensive
>> top-level design document for the DoS subsystem (e.g., a torspec or
>> proposal) that reflects the decisions that lead to the subsystem in its
>> current form.
>>
>> Specifically, we are looking at the DoS mitigation subsystem code for
>> entry guards at src/core/or/dos.{h,c} [1]. We are trying to understand
>> the chosen countermeasures and how the default and current consensus
>> values came to be, e.g., the decision to limit to 3 circuits per second
>> after the initial burst.
>>
>> 1) Could you kindly point us in the right direction if any such document
>> exists?
>>
>> 2) If it does not exist, would you mind briefly explaining how the DoS
>> threshold values (such as DoSCircuitCreationMinConnections,
>> DoSCircuitCreationRate, DoSCircuitCreationBurst, and
>> DoSConnectionMaxConcurrentCount) were chosen?
>>
> 
> Hello there,
> 
> first of all let me say that the DoS subsystem of Tor is under active
> development, so things are subject to change and mutate towards various
> directions (e.g. https://lists.torproject.org/pipermail/tor-dev/2020-April/014215.html).
> 
> However, since you are asking for resources on the currently existing
> DoS subsystem here is some things you can look at:
> 
> - Resources on general Tor rate limiting:
>             https://trac.torproject.org/projects/tor/ticket/24902 
>             https://lists.torproject.org/pipermail/tor-relays/2018-January/014357.html
> 
> - The proposal for the HS DoS subsystem:
>             https://github.com/torproject/torspec/blob/master/proposals/305-establish-intro-dos-defense-extention.txt
> 
> - More information on HS DoS subsystem:
>       https://lists.torproject.org/pipermail/tor-dev/2019-April/013790.html
>       https://lists.torproject.org/pipermail/tor-dev/2019-May/013837.html
>       https://lists.torproject.org/pipermail/tor-dev/2019-July/013923.html
> 
> Good luck with your research and please let us know if you reach the
> point where you can break or fix things! :)
> 
> Cheers!