rBridge: User Reputation based Tor Bridge Distribution with Privacy Preservation

Tor is one of the most popular censorship circumven-tion systems; it uses bridges run by volunteers as proxies toevade censorship. A key challenge to the Tor circumventionsystem is to distribute bridges to a large number of userswhile avoiding having the bridges fall into the hands ofcorrupt users. We propose rBridge—a user reputation sys-tem for bridge distribution; it assigns bridges according tothe past history of users to limit corrupt users from repeat-edly blocking bridges, and employs an introduction-basedmechanism to invite new users while resisting Sybil attacks.Our evaluation results show that rBridge provides muchstronger protection for bridges than any existing scheme.We also address another important challenge to the bridgedistribution—preserving the privacy of users’ bridge as-signment information, which can be exploited by maliciousparties to degrade users’ anonymity in anonymous commu-nication.