Improving Tor using a TCP-over-DTLS Tunnel

Abstract

The Tor network gives anonymity to Internet users by relaying their traffic through the world over a variety of routers. This incurs latency, and this thesis first explores where this latency occurs. Experiments discount the latency induced by routing traffic and computational latency to determine there is a substantial component that is caused by delay in the communication path. We determine that congestion control is causing the delay.

Tor multiplexes multiple streams of data over a single TCP connection. This is not a wise use of TCP, and as such results in the unfair application of congestion control. We illustrate an example of this occurrence on a Tor node on the live network and also illustrate how packet dropping and reordering cause interference between the multiplexed streams.

Our solution is to use a TCP-over-DTLS (Datagram Transport Layer Security) transport between routers, and give each stream of data its own TCP connection. We give our design for our proposal, and details about its implementation. Finally, we perform experiments on our implemented version to illustrate that our proposal has in fact resolved the multiplexing issues discovered in our system performance analysis. The future work gives a number of steps towards optimizing and improving our work, along with some tangential ideas that were discovered during research.

Additionally, the open-source software projects latency_proxy and libspe, which were designed for our purposes but programmed for universal applicability, are discussed.