No Direction Home: The True Cost of Routing Around Decoys

Decoy routing is a recently proposed approach for censorship circumvention. It relies on cooperating ISPs in the middle of the Internet to deploy the so called “decoy routers” that proxy network traffic from users in the censorship region. A recent study, published in an award-winning CCS 2012 paper [24], suggested that censors in highly connected countries like China can easily defeat decoy routing by selecting Internet routes that do not pass through the decoys. This attack is known as “routing around decoys” (RAD). In this paper, we perform an in-depth analysis of the true costs of the RAD attack, based on actual Internet data. Our analysis takes into account not just the Internet topology, but also business relationships between ISPs, monetary and performance costs of different routes, etc. We demonstrate that even for the most vulnerable decoy placement assumed in the RAD study, the attack is likely to impose tremendous costs on the censoring ISPs. They will be forced to switch to much more costly routes and suffer from degradation in the quality of service. We then demonstrate that a more strategic placement of decoys will further increase the censors’ costs and render the RAD attack ineffective. We also show that the attack is even less feasible for censors in countries that are not as connected as China since they have many fewer routes to choose from. The first lesson of our study is that defeating decoy routing by simply selecting alternative Internet routes is likely to be prohibitively expensive for the censors. The second, even more important lesson is that a fine-grained, data-driven approach is necessary for understanding the true costs of various route selection mechanisms. Analyses based solely on the graph topology of the Internet may lead to mistaken conclusions about the feasibility of decoy routing and other censorship circumvention techniques based on interdomain routing.