4 ms·

> While these relays account for 6% of the total number of exit relays, they only sum up to 2.7% of exit probability, which is what really matters. If that pro

> While these relays account for 6% of the total number of exit relays, they only sum up to 2.7% of exit probability, which is what really matters. If that probability is on a per-tor-session basis, that is actually not very in favor of the user. My combinatorics are a bit rusty, but wouldn't your odds of being in the 2.7% increase significantly each time you use the tor network?

sp332 12y ago
After 25 times, you'd have a 50/50 chance of having gone through those nodes at least once.
- LunaSea 12y ago
  I don't think so because the chance of using a node is an independent event. So you will most likely have the same chance every time.
  - deleted 12y ago
    [deleted]
  - sp332 12y ago
    Right! I mean cumulatively, after connecting 25 times, you have a 50/50 chance that at least one of those connections went through one of these nodes. (1 - 0.027) ^ 25 ~= 0.5
    - tga_d 12y ago
      Nit: I think that should be 1-(1-.0.27)^25 ~= 0.5. Obviously it ends up being about 1/2 either way, but you're measuring the chance that you used one of the nodes, not that you avoided all of them.
garrettr_ 12y ago
Tor uses entry guards [0] to mitigate this kind of an attack. [0]: https://www.torproject.org/docs/faq.html.en#EntryGuards https://www.torproject.org/docs/faq.html.en#EntryGuards
- nullc 12y ago
  Entry guards do nothing for bad exits... sticking to particular exits across sessions would significantly harm your privacy in a way that entry guards do not.
tga_d 12y ago
Your Tor session should change exit nodes at least once every 10 minutes.[1] Ignoring everything else (e.g. pressing the new session button on TBB, restarting the browser, failed connections etc.), this gives us p(using a bad node)=1-(.973)^(t/10) where t is how many minutes you've been using Tor. So if you've actively used Tor for more than 4 1/2 hours over the past month, it's more likely than not that you've used one of these nodes. [1] https://www.torproject.org/docs/faq.html.en#ChangePaths https://www.torproject.org/docs/faq.html.en#ChangePaths

sp332 12y ago

After 25 times, you'd have a 50/50 chance of having gone through those nodes at least once.

LunaSea 12y ago
I don't think so because the chance of using a node is an independent event. So you will most likely have the same chance every time.
- deleted 12y ago
  [deleted]
- sp332 12y ago
  Right! I mean cumulatively, after connecting 25 times, you have a 50/50 chance that at least one of those connections went through one of these nodes. (1 - 0.027) ^ 25 ~= 0.5
  - tga_d 12y ago
    Nit: I think that should be 1-(1-.0.27)^25 ~= 0.5. Obviously it ends up being about 1/2 either way, but you're measuring the chance that you used one of the nodes, not that you avoided all of them.

garrettr_ 12y ago

Tor uses entry guards [0] to mitigate this kind of an attack. [0]: https://www.torproject.org/docs/faq.html.en#EntryGuards https://www.torproject.org/docs/faq.html.en#EntryGuards

nullc 12y ago
Entry guards do nothing for bad exits... sticking to particular exits across sessions would significantly harm your privacy in a way that entry guards do not.

tga_d 12y ago

Your Tor session should change exit nodes at least once every 10 minutes.[1] Ignoring everything else (e.g. pressing the new session button on TBB, restarting the browser, failed connections etc.), this gives us p(using a bad node)=1-(.973)^(t/10) where t is how many minutes you've been using Tor. So if you've actively used Tor for more than 4 1/2 hours over the past month, it's more likely than not that you've used one of these nodes. [1] https://www.torproject.org/docs/faq.html.en#ChangePaths https://www.torproject.org/docs/faq.html.en#ChangePaths