[tor-bugs] #5458 [Tor Client]: Clients should warn and disable guards responsible for excessive circuit failures

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#5458: Clients should warn and disable guards responsible for excessive circuit
failures
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 Reporter:  mikeperry        |          Owner:  mikeperry         
     Type:  defect           |         Status:  needs_review      
 Priority:  major            |      Milestone:  Tor: 0.2.3.x-final
Component:  Tor Client       |        Version:                    
 Keywords:  MikePerry201206  |         Parent:  #5456             
   Points:  6                |   Actualpoints:                    
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Changes (by nickm):

  * status:  needs_revision => needs_review


Comment:

 I pushed a "bug5458" to my repository that handles all of my issues above
 other than:

  * A four-hop circuit IMO doesn't need special treatment. A cannibalized
 circuit, though, will get counted as having succeeded twice, which isn't
 necessarily what we want. This could throw off results if a large enough
 fraction of circuits gets cannibalized.
  * Is it possible to have PATH_BIAS_MIN_CIRCS on a guard all in progress
 at once? If so, there might be an annoying problem when starting up a new
 guard.
  * We should do the math to see how successful the attack can be under
 different parameter choices. (Under the current parameter choices, it
 seems like you can do route capture pretty darn effectively so long as you
 treat each new client honestly for a sufficiently large number of circuits
 before doing the attack.)
  * We should figure out what kind of false positive rate we expect, and
 document that, and maybe even mention it in the warning. (A tiny but not
 vanishing false positive rate, multiplied by a very large number of users
 and a lot of time, means that we should expect some number of spurious
 reports.)

 Totally untested!  Needs review.  Also:

  * Needs a path-spec.txt writeup.
  * Needs a changes file.
  * Needs to have the new parameters noted in dir-spec.

 Also Mike Perry owes me a tasty beverage, to be added to the innumerable
 tally of tasty beverages that Mike and I owe one another.  And if the
 ratio of beverages ordered to bevereges enjoyed becomes too high, we need
 to move to another restaurant.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/5458#comment:22>
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