[tor-bugs] #3678 [Tor Client]: Disallow more than one relay per country in a circuit

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#3678: Disallow more than one relay per country in a circuit
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 Reporter:  cypherpunks  |          Owner:                   
     Type:  enhancement  |         Status:  needs_information
 Priority:  major        |      Milestone:                   
Component:  Tor Client   |        Version:                   
 Keywords:               |         Parent:                   
   Points:               |   Actualpoints:                   
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Comment(by cypherpunks):

 Replying to [comment:11 cypherpunks]:
 > Replying to [comment:8 cypherpunks]:
 > >
 > > What nickm said is that IX points are the threat. Why is there not
 more research done on this level?  Is it not core to Tor's anonymity?
 >
 > Perhaps "why hasn't tor implemented anything related to this research?"
 is a better question.

 With an easier answer: what to implement is far from clear. Tor's /16
 independence for nodes in circuits actually does help with this problem.
 So, Tor _has_ implemented something related to this research. But it's
 very far from perfect, as a small example, found that even nodes in
 different /8s can share an AS. And if your circuit is entering or leaving
 the Tor network in parts of Europe, then the risk that it passes through
 the same IX makes this worse; although I don't know precisely how much.
 The AS-awareness paper does suggest and analyze ways to significantly
 improve path independence for links, but they involve a nontrivial
 increase in overhead of what is distributed to clients and the cost to the
 client of choosing nodes for circuits.

 > It seems IX points are the problem.  The AS paper doesn't seem to matter
 much.

 Can you explain? Do you mean because IXes are bigger aggregation points?
 The three AS and IX papers mentioned are addressing essentially the same
 problem, just different aspects of it. And the two AS papers (not sure
 which one you meant) show even just the path-independence concern is
 significant. And growth of the network has not helped (sometimes made it
 worse). And this is not the only risk of attack on the links, just the
 most salient one.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/3678#comment:14>
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