Re: [tor-talk] Why adding Guard-Exit (EE) node in Tor yeild more catch probability than adding guard and exit node separately?

[saurav dahal <dahal.saurav@xxxxxxxxx>]

Hello,

The following is the default Tor network in shadow simulator:

Total BW of Guard flagged nodes=258.15 MB/S
Total BW of Middle nodes=23.69 MB/S
Total BW of Exit flagged nodes=13.23 MB/S
Total BW of Guard+Exit flagged nodes=213.4 MB/S

Now, I inserted 40 guard nodes and 40 exit nodes, each of 5 MB/S in above
Tor network and performed the simulation.

Following are the bandwidth weights derived from the consensus document
when Guard and Exit nodes of 5MB/S are added separately:


Wbd=1454 Wbe=0 Wbg=4882 Wbm=10000 Wdb=10000 Web=10000 Wed=7091 Wee=10000
Weg=7091 Wem=10000 Wgb=10000 Wgd=1454 Wgg=5118 Wgm=5118 Wmb=10000 Wmd=1454
Wme=0 Wmg=4882 Wmm=10000


Then again, I added 80 Guard-Exit (EE) nodes, each 5MB/S and perform the
simulation.


Following are the bandwidth weights derived from the consensus document
when EE nodes of 5MB/S are added:


Wbd=4722 Wbe=0 Wbg=0 Wbm=10000 Wdb=10000 Web=10000 Wed=4826 Wee=10000
Weg=4826 Wem=10000 Wgb=10000 Wgd=452 Wgg=10000 Wgm=10000 Wmb=10000 Wmd=4722
Wme=0 Wmg=0 Wmm=10000


I calculated catch probability in both cases and found that the 2nd case
yields more probability.


By examining the above weights, how it is possible that the catch
probability for EE nodes are much higher than those of guard and exit node
separately? OR is there any other reason for this?


Can anybody please explain this?


Thanks,


On Wed, Aug 6, 2014 at 11:20 AM, saurav dahal <dahal.saurav@xxxxxxxxx>
wrote:

> Hi Matt,
>
> If I understand correctly, you ran a simulation where you had x nodes
> which had the Guard flag and y exit nodes..
>
> Yes.
>
> then you ran another simulation where you had (x+y) exit nodes which also
> had the Guard flag? Is this correct?
>
> No.
>
> In simulation, there is node which has both Guard and exit flag, so called
> guard-exit node (EE node). I put (x+y) EE node and ran the simulation.
>
> Please refer to the shadow wiki below
>
> https://github.com/shadow/shadow/wiki/Using-the-scallion-plug-in
>
> Here you can see Guard+Exit relays.
>
> Thanks,
> Saurav
>
>
>
>
> On Wed, Aug 6, 2014 at 1:57 AM, Matthew Finkel <matthew.finkel@xxxxxxxxx>
> wrote:
>
>> On Tue, Aug 05, 2014 at 10:40:17AM +0900, saurav dahal wrote:
>> > I am trying to observe the catch probability i.e. probability that a
>> client
>> > selects my added guard as well as exit node while making a circuit.
>> >
>> > First I inserted certain number of guard nodes and certain number of
>> exit
>> > nodes in Tor network and performed the simulation in Shadow simulator.
>> > After completion of simulation, I calculated the catch probability.
>> >
>> > Then again I added the same number of Guard-Exit (EE) node and perform
>> the
>> > simulation and calculated the probability.
>> >
>> > I found that catch probability for EE nodes are much higher than those
>> of
>> > guard and exit node separately.
>> >
>> > Could anyone please explain why this happened?
>>
>> Hi Saurav,
>>
>> Can you clarify what you mean by Guard-Exit nodes? If I understand
>> correctly, you ran a simulation where you had x nodes which had the
>> Guard flag and y exit nodes, then you ran another simulation where
>> you had (x+y) exit nodes which also had the Guard flag? Is this
>> correct?
>>
>> Thanks,
>> Matt
>> --
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>
>
>
> --
>
> Saurav Dahal,
> Wireless communication and Networking lab,
> Dept. of Computer Engineering,
> Chosun University,
> 309 Pilmun-daero, Dong-gu
> Gwangju, 501-759 S.KOREA
>



-- 

Saurav Dahal,
Wireless communication and Networking lab,
Dept. of Computer Engineering,
Chosun University,
309 Pilmun-daero, Dong-gu
Gwangju, 501-759 S.KOREA
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