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Re: [tor-bugs] #8163 [Core Tor/Tor]: It is no longer deterministic which Sybils we omit
#8163: It is no longer deterministic which Sybils we omit
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Reporter: arma | Owner: (none)
Type: defect | Status: new
Priority: Medium | Milestone: Tor:
| unspecified
Component: Core Tor/Tor | Version: Tor:
| 0.2.4.10-alpha
Severity: Normal | Resolution:
Keywords: tor-dirauth sybil voting needs-spec | Actual Points:
Parent ID: | Points:
Reviewer: | Sponsor:
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Comment (by teor):
Replying to [comment:24 arma]:
> So, I think an evil person could manipulate which dir auths it responds
to, to get a 2x increase in Sybils per IP address. But I think it's capped
at 2x, because we demand a majority of Running votes from each dir auth to
put you in the consensus.
It's strictly less than 2x.
With AuthDirMaxServersPerAddr 2:
* there are 9*2 = 18 Running-votes per IPv4 address
* a majority is 5/9
* 18/5 = 3
With AuthDirMaxServersPerAddr 4:
* there are 9*4 = 36 Running-votes per IPv4 address
* a majority is 5/9
* 36/5 = 7
3 extra relays is a significant jump from 1 extra relay.
Maybe we should fix this bug by adding a tie-breaker to the comparison?
If we want the "best" relays, and we want convergent behaviour, we should
sort by Running, weighted fractional uptime, then fingerprint to break
zero-uptime ties.
But it's still possible to game those checks, so we should:
* add AuthDirMaxServersPerAddr as a consensus parameter, hard-coded to the
value of the AuthDirMaxServersPerAddr torrc option
* add a new consensus method that only chooses the first
AuthDirMaxServersPerAddr relays per IP address, sorting by Running, then
fingerprint
These bugs shouldn't be that hard to fix.
Do we have a sponsor for it?
It fits within the broad topic of Sponsor V, but it's not in scope for any
of the deliverables.
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/8163#comment:25>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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