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Tor Project Mulls How Feds Took Down Hidden Websites
HughPickens.com writes: Jeremy Kirk writes at PC World that in the aftermath of U.S. and European law enforcement shutting down more than 400 websites (including Silk Road 2.0) which used technology that hides their true IP addresses, Tor users are asking: How did they locate the hidden services? "The first and most obvious explanation is that the operators of these hidden services failed to use adequate operational security," writes Andrew Lewman, the Tor project's executive director. For example, there are reports of one of the websites being infiltrated by undercover agents and one affidavit states various operational security errors." Another explanation is exploitation of common web bugs like SQL injections or RFIs (remote file inclusions). Many of those websites were likely quickly-coded e-shops with a big attack surface. Exploitable bugs in web applications are a common problem says Lewman adding that there are also ways to link transactions and deanonymize Bitcoin clients even if they use Tor. "Maybe the seized hidden services were running Bitcoin clients themselves and were victims of similar attacks."
However the number of takedowns and the fact that Tor relays were seized could also mean that the Tor network was attacked to reveal the location of those hidden services. "Over the past few years, researchers have discovered various attacks on the Tor network. We've implemented some defenses against these attacks (PDF), but these defenses do not solve all known issues and there may even be attacks unknown to us." Another possible Tor attack vector could be the Guard Discovery attack. The guard node is the only node in the whole network that knows the actual IP address of the hidden service so if the attacker manages to compromise the guard node or somehow obtain access to it, she can launch a traffic confirmation attack to learn the identity of the hidden service. "We've been discussing various solutions to the guard discovery attack for the past many months but it's not an easy problem to fix properly. Help and feedback on the proposed designs is appreciated."
According to Lewman, the task of hiding the location of low-latency web services is a very hard problem and we still don't know how to do it correctly. It seems that there are various issues that none of the current anonymous publishing designs have really solved. "In a way, it's even surprising that hidden services have survived so far. The attention they have received is minimal compared to their social value and compared to the size and determination of their adversaries."
However the number of takedowns and the fact that Tor relays were seized could also mean that the Tor network was attacked to reveal the location of those hidden services. "Over the past few years, researchers have discovered various attacks on the Tor network. We've implemented some defenses against these attacks (PDF), but these defenses do not solve all known issues and there may even be attacks unknown to us." Another possible Tor attack vector could be the Guard Discovery attack. The guard node is the only node in the whole network that knows the actual IP address of the hidden service so if the attacker manages to compromise the guard node or somehow obtain access to it, she can launch a traffic confirmation attack to learn the identity of the hidden service. "We've been discussing various solutions to the guard discovery attack for the past many months but it's not an easy problem to fix properly. Help and feedback on the proposed designs is appreciated."
According to Lewman, the task of hiding the location of low-latency web services is a very hard problem and we still don't know how to do it correctly. It seems that there are various issues that none of the current anonymous publishing designs have really solved. "In a way, it's even surprising that hidden services have survived so far. The attention they have received is minimal compared to their social value and compared to the size and determination of their adversaries."
If you DDOS a site using TOR it'll saturate all possible exit nodes.
Inevitably one of these exit nodes will be owned by the feds.
I wonder if they're doing their tracking by just sending traffic the servers in question from multiple places and with control over a few exit nodes. They'd basically be sending seismic waves through Tor and timing the responses. After a while and with enough exit nodes you could start figuring out where the other nodes are. With enough traffic analysis from ISPs or whatever you could find out where the TOR nodes actually are. At that point it becomes easier to figure out physically where they are.
This is theoretical, but it would be fun to try.
As I understand the Tor process, every tine I fire up Tor it randomly chooses an exit node(*).
Suppose I am running some exit nodes (as the NSA is suspected of doing). If I want to find the location of a hidden service I just fire up Tor and access an onion website with a specific tempo. If one of my exit nodes shows traffic with that tempo, then I know that's the exit node for this onion connection and I can trace the exit connection(**).
If you access the site many times, eventually the statistical nature of the tempo (in your own exit node) will be apparent among the random noise of other traffic. If you do the process many times, eventually you'll find a strong statistical evidence for the target IP address.
How many Tor exit nodes does the FBI run? How much time can they put into discovering each site? Can tempo-based access be automated?
See here for more info. From a paper published in 2011 comes the quote:
This would be my guess.
(*) For the onion protocol it's listed as a rendezvous point and there's some protocol negotiation, but it's essentially an exit node.
(**) Actually it's even simpler. Tor reports the IP address of your exit node - just keep starting Tor until the exit node is a system you control.