Honey Onions: Exposing Snooping Tor HSDir Relays presented at Defcon 2016

by Amirali Sanatinia, Guevara Noubir,

Summary : Tor is a widely used anonymity network that protects users' privacy and and identity from corporations, agencies and governments. However, Tor remains a practical system with a variety of limitations, some of which were indeed exploited in the recent past. In particular, Tor's security relies on the fact that a substantial number of its nodes do not misbehave.
Previous work showed the existence of malicious participating Tor relays. For example, there are some Exit nodes that actively interfere with users' traffic and carry out man-in-the-middle attacks. In this work we expose another category of misbehaving Tor relays (HSDirs), that are integral to the functioning of the hidden services and the dark web. The HSDirs act as the DNS directory for the dark web. Because of their nature, detecting their malicious intent and behavior is much harder. We introduce, the concept of honey onions (honions), a framework to detect misbehaving Tor relays with HSDir capability. By setting up and deploying a large scale honion over Tor for more than 72 days, we are able to obtain lower bounds on misbehavior among HSDirs.
We propose algorithms to both estimate the number of snooping HSDirs and identify them, using optimization and feasibility techniques. Our experimental results indicate that during the period of our work at least 110 such nodes were snooping information about hidden services they host. We reveal that more than half of them were hosted on cloud infrastructure and delayed the use of the learned information to prevent easy traceback. Furthermore, we provide the geolocation map of the identified snooping Tor HSDirs