Unfortunately I had to significantly throttle down creating this blog recently – this is partially due to stacking up of ‘usual’ responsibilities, but also partially due to the fact that I’m involved in organization of law / IT conference – Net Attacks 2014 which happens at Nicolaus Copernicus University in Torun. It might be the only event in Poland that enables discussion between lawyers, netsec professionals and government agencies – be sure to check it out at http://www.atakisieciowe.umk.pl/. Beside taking part in organizing I’m also preparing lecture on law enforcement’s struggle with anonymity provide by Tor. Here I’d like to present sneak peak of my research combined with some thoughts that probably won’t make it to the final cut of the lecture / article.
It’s indisputable that Tor bundle changed fundamentally access to Internet anonymity. Ease of use and almost foolproof mechanism were the elements which guaranteed massive popularity, as well as made it perfect platform for some forms of criminal activity. Drug dealing and child pornography exchange are primary examples of such use. Level of protection delivered by Tor is more than enough to evade law enforcement and with minimal additional knowledge and care render conventional investigation techniques completely useless. In this circumstances LEA are basically left with three options: leveraging very design of Tor, utilize 0-day exploits on software of Tor bundle and basically hack the machines of criminals or use social engineering combined with leveraging carelessness of users to gain data sufficient to capture criminals. However, it is important to remember that law enforcement is bind by law which in many cases is far behind bleeding edge of technology. This situation is especially apparent in civil law countries where often every action taken by LEA have to be strictly detailed in law acts with very little room to adjust to changing situation. Of course it is equally important to keep in mind civil liberties and human rights aspect. Such detailed instruction makes all the operations very transparent and keep agents from abusing their power. On the other hand perhaps more relaxed in terms of legislation, but based on court warrants system allows better adaptation to specific cases.
Two greatest ‘weakness by design’ aspects of Tor are vulnerability to global passive adversary and lack of encryption of data leaving exit nodes. First still seems to remain in the realm of theory and it’s not likely it will become significant option for law enforcement. Even though experiments prove their effectiveness, resources required to pull such operation off and need for basically blanket approval to sniff on extremely large chunks of network make it impossible to use in any country with even elemental privacy safeguards. Second option (exit node eavesdropping) is definitely more interesting both in technical and legal terms. First of all it does work great! Experiment presented by Swedish researcher Dan Egerstad proved that setting up even small exit nodes in various locations can yield amazing results with captured emails from various embassies and government agencies. Furthermore Egerstad claimed that both some of these accounts were already compromised be people using similar technique and that some large exit nodes are just to conveniently placed in places like Washington D.C. and have to large bandwidth not to be set up by the government. And while up to this point everything sounds great it is still probably poor method for crime fighting. First of all blatant capture and analysis of all data that leaves certain node in on par with massive blanket surveillance that we are aware of now, after Snowden’s revelation. As such it should be discouraged, and if used will face the same problems with using it as evidence as NSA programs are facing now. Also let’s not omit the fact than exit node sniffing does not reveal IP addresses, only messages sent.
However, FBI took entirely different route when trying to break child pornography circles. After capturing creator of Freedom Hosting, and at the same time gaining control of its servers, agents injected malware on services hosted by FH. Malware wasn’t anything spectacular and required carelessness on the side of Tor user, but proved to be good enough for its job. At the same time though, it opens the discussion about limits of tools LEA can use. The exploit used was a 0 day for Firefox, using it meant basically exposing every other browser with the same configuration and same version to be attacked. On the other hand exploit was already outdated when released since latest release of Firefox was already patched against it. Since use of such technologies is relatively new it is not surprising that law is far behind. In Poland doing anything similar would be probably impossible to do, not even due to harsh restrains on LEAs but because there is nothing even remotely similar discussed in Polish legislation.
Finally there is a case of Dread Pirate Robers and whole series of events that lead to his identification. However if you would like to hear about that please join me at Net Attacks 2014 🙂