Abstract
Tor is the most popular anonymous communication tool in the world. Its anonymity, however, has not been thoroughly evaluated. For example, it is possible for an adversary to restrict access to the Tor network by blocking all the publicly listed relays. In response, Tor utilizes bridges, which are unlisted relays, as alternative entry points. However, the vulnerabilities of the current bridge mechanism have not been thoroughly investigated yet. We first investigate the vulnerabilities of the current bridge mechanism under different adversarial models. Then we compare the current bridge mechanism with our two proposals and discuss their effects on the security and performance of Tor.
