rBridge: User Reputation based Tor Bridge Distribution with Privacy Preservation

Tor is one of the most popular censorship circumvention systems; it uses bridges run by volunteers as proxies to evade censorship. A key challenge to the Tor circumvention system is to distribute bridges to a large number of users while avoiding having the bridges fall into the hands of corrupt users. We propose rBridge-a user reputation system for bridge distribution; it assigns bridges according to the past history of users to limit corrupt users from repeatedly blocking bridges, and employs an introduction-based mechanism to invite new users while resisting Sybil attacks. Our evaluation results show that rBridge provides much stronger protection for bridges than any existing scheme. We also address another important challenge to the bridge distribution-preserving the privacy of users' bridge assignment information, which can be exploited by malicious parties to degrade users' anonymity in anonymous communication.