[tor-talk] WFU, Entry Guards and Service Location Attack

Christoph Schulthess cjschulthess at googlemail.com
Sat Oct 5 13:28:21 UTC 2013

Hi everyone,

I've been thinking and reading a bit about Tor and especially hidden
servers, now I have a couple of questions:

1. What are the exact criteria for applying the guard flag to a relay? The
older blog entry at
https://blog.torproject.org/category/tags/entry-guardsnames 3 criteria
with exact numbers but there is a newer post which
suggests that the system has been changed since 2011.

2. How is the Weighted Fractional Uptime number calculated exactly? Could
you give an quick example? I found one explanation online but when I
calculated it, I always got quite different numbers than the example that
was given.

3. The Locating-paper mentions three attacks to locate hidden servers and
the entry guard concept as effective countermeasure. I understand how entry
guards protect from the predecessor attack and the distance attack, but so
far I don't see how they prevent the service location attack. Is there
another countermeasure against that kind of attack or did I miss something?

Would be great if anyone could help me out.


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