A recent study on the ability to discover the identities of users of the anonymous Tor (The Onion Router) has caused quite a stir in the online community. So much so that the project's developers issued a statement to calm things down somewhat, stating that the rate of false positives makes attacks of this type useless.
The study was published after six years of research by Professor Sambuddah Chakravarty of the Indraprastha Institute of Computer Science, New Delhi. In short, the professor says that 81% of the IP addresses of Tor network users can be revealed through the analysis of traffic collected by Cisco routers using NetFlow technology. You can find the study On the Effectiveness of Traffic Analysis Against Anonymity Networks Using Flow Records, here (PDF).
Chakravarty stated that under laboratory conditions he was able to reveal all the anonymous addresses. When the technique was tested in real conditions, the accuracy dropped to 81.4% and a false positive rate of 12.2% was recorded.
The false positive rate was 6.4%. According to Roger Dingledine, a development manager for the Tor project, this value is extremely important, because it shows that on a large scale, the entire attack looks like someone is looking for a needle in a haystack. Thus, he argues that the attack is ineffective.
Chakravarty's project is based on identifying similarities in the flow patterns of traffic entering and leaving the Tor network. NetFlow data is not yet sufficiently refined, and to compensate for this disadvantage, the type of attack proposed by the researcher requires a server controlled by the attacker and "introduces deterministic perturbations in the traffic of anonymous visitors."
This could be part of a government's plan, or a surveillance service, designed to monitor the traffic passing through the Tor network servers at various points. The other viewpoint, coming from the Tor Project development lead, states that users still have no reason to fear that their identity can be exposed when using Tor.
The truth is probably somewhere in the middle, but the proverb is well known, “if you don’t praise your house it will fall and crush you.”
