The Tor Project said on Friday that the online anonymity network may go dark in coming days due to an attempt to incapacitate it.
The project’s leader Roger Dingledine aka “arma” drew attention to the possible outage on the project’s blog, flagging a tip-off that its directory authority servers — a handful of servers that form a consensus on which relays that Tor clients should use — may be the target of an upcoming “seizure".
“The Tor Project has learned that there may be an attempt to incapacitate our network in the next few days through the seizure of specialized servers in the network called directory authorities,” Dingledine warned.
The wording of the alert suggests that the attacker is law enforcement rather than hackers. Should an attacker gain control of a majority of those servers, they would be able to vote in a fake Tor network.
As the project explains in its FAQ: “The directory authorities provide a signed list of all the known relays, and in that list are a set of certificates from each relay (self-signed by their identity key) specifying their keys, locations, exit policies, and so on. So unless the adversary can control a majority of the directory authorities (as of 2012 there are 8 directory authorities), he can't trick the Tor client into using other Tor relays.”
A thread on Hacker News notes there are actually now nine directory authorities located across Europe and the US, so the attackers would need to gain control of five in order point Tor users to a phoney Tor network.
“We are taking steps now to ensure the safety of our users, and our system is already built to be redundant so that users maintain anonymity even if the network is attacked. Tor remains safe to use,” Dingledine noted.
It’s not clear what the motivation is for the possible seizure, nor which authority may be behind it. However, there is speculation it may be related to the Sony Pictures investigation due to the hackers having used Tor in the attack.
“The attackers appear to have used TOR exit nodes and VPNs to help cover their tracks, which indicates some awareness of operational security (OPSEC),” HP noted.
But as Dingledine noted in further comments, if the FBI were to seize a majority of the nine directory authorities it would not help them identify what individual Tor users had done in the past or were doing presently.
“If they're trying to hunt down particular Tor users, most possible attacks on directory authorities would be unproductive, since those relays don't know anything about what particular Tor users are doing,” he noted.
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