The Path Less Travelled: Overcoming Tor’s Bottlenecks with Multipaths

Tor is the most popular low-latency anonymity network for enhancing ordinary users’ online privacy and resisting censorship. While it has grown in popularity, Tor has a variety of performance problems that result in poor quality of service, a strong disincentive to use the system, and weaker anonymity properties for all users. We observe that one reason why Tor is slow is due to lowbandwidth volunteer-operated routers. When clients use a low-bandwidth router, the throughput of their traffic is limited by the capacity of the slowest node. With the introduction of Tor bridges—unadvertised Tor routers that provide Tor access to users within censored regimes like China—low-bandwidth Tor routers are becoming more common and essential to Tor’s ability to resist censorship. In this paper, we present Tempura, a multipath circuit construction and streamsplitting approach that increases performance for clients using bandwidth-deprived bridges. Moreover, Tempura significantly improves the experience of users who watch streaming videos online. Through live measurements and a whole-network evaluation conducted on a scalable network emulator, we show that our approach offers an improvement of approximately 30% in expected download time for web browsers who use Tor bridges and for streaming application users. We also show that our scheme has no significant impact on users’ security or anonymity.