We’ve been speaking to journalists who are curious about a HotPETS 2016 talk from last week: the HOnions: Towards Detection and Identification of Misbehaving Tor HSDirs research paper conducted by our colleagues at Northeastern University. Here's a short explanation, written by Donncha and Roger.

Internally, Tor has a system for identifying bad relays. When we find a bad relay, we throw it out of the network.

But our techniques for finding bad relays aren't perfect, so it's good that there are other researchers also working on this problem. Acting independently, we had already detected and removed many of the suspicious relays that these researchers have found.

The researchers have sent us a list of the other relays that they found, and we're currently working on confirming that they are bad. (This is tougher than it sounds, since the technique used by the other research group only detects that relays *might* be bad, so we don't know which ones to blame for sure.)

It's especially great to have this other research group working on this topic, since their technique for detecting bad relays is different from our technique, and that means better coverage.

As far as we can tell, the misbehaving relays' goal in this case is just to discover onion addresses that they wouldn't be able to learn other ways—they aren't able to identify the IP addresses of hosts or visitors to Tor hidden services.

The authors here are not trying to discover new onion addresses. They are trying to detect other people who are learning about onion addresses by running bad HSDirs/relays.

This activity only allows attackers to discover new onion addresses. It does not impact the anonymity of hidden services or hidden service clients.

We have known about and been defending against this situation for quite some time. The issue will be resolved more thoroughly with the next-generation hidden services design. Check out our blog post, Mission: Montreal!