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Re: [tor-bugs] #6526 [Tor]: Implement directory guards
#6526: Implement directory guards
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Reporter: rransom | Owner:
Type: defect | Status: needs_review
Priority: normal | Milestone: Tor: 0.2.4.x-final
Component: Tor | Version:
Keywords: tor-client prop207 dir-guards | Parent:
Points: | Actualpoints:
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Comment(by mikeperry):
In addition to my comments on tor-dev, there's another reason to use the
same list for each: client fingerprintability. If we keep two separate
lists, your combined set of Guards+DirectoryGuards is absolutely
fingerprintable as you move your tor client from IP to IP.
For some back of the envelope calculations, the current Guard entropy is
~9 bits. This is equivalent to 512 equal-sized guard choices. If we scale
back to 2 guards, we have:
https://www.wolframalpha.com/input/?i=512+choose+2
However, if we use 3 directory guards + 2 guards:
https://www.wolframalpha.com/input/?i=512+choose+5
Neither are great, but the 2-guard case already doesn't segment our
userbase, and will certainly experience enough change to damage the
fingerprint as Guards go up and down while clients are offline/inactive.
It seems unlikely that such rotation will make a significant impact on the
5-guard case's tremendous fingerprintability, though.
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/6526#comment:8>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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