[metrics-team] PrivCount in Tor session in Rome

[Karsten Loesing]

On 2018-03-13 12:06, teor wrote:
> 
>> On 13 Mar 2018, at 11:41, Karsten Loesing <karsten at torproject.org> wrote:
>>
>> Hi teor,
>>
>>> On 2018-03-13 09:00, teor wrote:
>>>>> 2. What analysis can the metrics team do to help with PrivCount
>>>>> design/development? There's something in the notes about flags changing
>>>>> in 24 hour periods or possible partition of relays. Can you elaborate
>>>>> and make these questions a lot more concrete? Maybe this is something I
>>>>> can do in the next few days, with enough time for you to discuss more
>>>>> with irl while you're in Rome?
>>>>
>>>> We want to partition the reporting relays into 3 groups at random.
>>>> (Or maybe some other number: there is a tradeoff between the number of
>>>> groups, which resists manipulation by a single relay, and the quality of the
>>>> resulting statistic.)
>>>>
>>>> If we select relays from the consensus at random, do we get a roughly
>>>> even distribution of consensus weight, guard weight, middle weight, and
>>>> exit weight?
>>>>
>>>> What if we only have 5% of relays reporting statistics?
>>>> Can we still get roughly even total partition weights at random?
>>>> (Please choose relays on the latest tor versions, because they will be the
>>>> first to deploy PrivCount.)
>>
>> Here's a graph (with and without annotations):
>>
>> https://people.torproject.org/~karsten/volatile/partitions-2018-03-13.pdf
>>
>> https://people.torproject.org/~karsten/volatile/partitions-2018-03-13-annotated.pdf
> 
> 0.3.2 has the expected consensus weight distribution.
> And it's 2 months since 0.3.2 became stable:
> https://trac.torproject.org/projects/tor/wiki/org/teams/NetworkTeam/CoreTorReleases
> 
> I would be happy to wait 2 months after a stable release for good statistics.
> 
>> Let me know if this makes sense, or which parameters I should tweak.
> 
> Can we focus on 0.3.2, and all relays?

That would be 0.3.2 or higher then. And all relays for comparison. Sure!

>> For
>> example:
>>
>> - Different number of groups (currently 3).
> 
> Can we try 3 and 5?

Yep!

>> - Different number of simulations (currently 1000).
> 
> That's fine.

Or, 40 simulations per consensus = 40 * 24 = 960 simulations in total.

>> - Different number of consensuses as input (currently 1).
> 
> We'll be collecting over a day, so please use 24 consensuses.

Okay. Note that I'm simply taking 24 consensuses rather than 1 and
running simulations on that. I'm not tracking how relays stay online
over these 24 hours. That would be a different simulation.

>>>> If we can't get even partitions by choosing relays at random, we will need
>>>> to choose partitions weighted by consensus weight. Let's decide if we
>>>> want to do that analysis after we see the initial results.
>>
>> Let me know if you want me to try out a different algorithm. The current
>> algorithm simply assigns relays to groups at random.
> 
> That seems to get us what we want, let's keep selecting at random.

Alright.

New graph:

https://people.torproject.org/~karsten/volatile/partitions-2018-03-13a.pdf

All the best,
Karsten

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