The Tor Project has moved to allay concerns about the privacy of its users after new research claimed to be able to reveal the sources of anonymous traffic in 81% of real-world experiments, albeit with high false positives.
The research, On the Effectiveness of Traffic Analysis Against Anonymity Networks Using Flow Records, was led by Columbia University’s Sambuddho Chakravarty.
He claims that a “powerful adversary,” for example a nation state, could successfully link together otherwise unrelated network connections in a traffic analysis attack.
Said traffic analysis is made possible by “deliberately perturbing the characteristics of user traffic at the server side, and observing a similar perturbation at the client side through statistical correlation,” he said.
The abstract continues:
“Previous research has shown that having access to a few internet exchange points is enough for monitoring a significant percentage of the network paths from Tor nodes to destination servers. Although the capacity of current networks makes packet level monitoring at such a scale quite challenging, adversaries could potentially use less accurate, but readily available traffic monitoring functionality, such as Cisco’s NetFlow, to mount large-scale traffic analysis attacks.”
The Tor Project welcomed the research but maintained traffic correlation attacks are nothing new and are difficult to achieve at scale:
“Sambuddho's paper mentions a false positive rate of 6%. That sounds like it means if you see a traffic flow at one side of the Tor network, and you have a set of 100,000 flows on the other side and you're trying to find the match, then 6,000 of those flows will look like a match. It's easy to see how at scale, this ‘base rate fallacy’ problem could make the attack effectively useless.”
Lancope CTO, TK Keanini, argued that even if the flaw were serious and could be exploited at scale, Tor would remediate to protect its users.
“Realize that even if Tor went away, another would quickly fill its place, because the need for anonymity in the net is in demand by all sides,” he told Infosecurity.
“It is important that folks who use Tor ensure that it is from a reliable source as compromised software is bad all around.”
Mark James, security specialist at Eset, argued that on the whole Tor is “as safe as it's ever been.”
"For the majority of users who use the service for web anonymity they will be safe in doing what they are currently doing without too much concern about losing their privacy," he told Infosecurity.
“The high amount of false positives shown from the recent paper would make the effort worthless on a large scale. However, as long as we understand there is no 100% anonymity on the internet and that it’s assumed that it is always possible for someone somewhere to find out where you have been or who you are, then 99% anonymity will be fine using Tor.”