Improving Tor using a TCP-over-DTLS Tunnel

The Tor network gives anonymity to Internet users by relaying their traffic through the world over a variety of routers. All traffic between any pair of routers, even if they represent circuits for different clients, are multiplexed over a single TCP connection. This results in interference across circuits during congestion control, packet dropping and packet reordering. This interference greatly contributes to Tor’s notorious latency problems. Our solution is to use a TCP-over-DTLS (Datagram Transport Layer Security) transport between routers. We give each stream of data its own TCP connection, and protect the TCP headers—which would otherwise give stream identification information to an attacker—with DTLS. We perform experiments on our implemented version to illustrate that our proposal has indeed resolved the cross-circuit interference.