TorBricks: Blocking-Resistant Tor Bridge Distribution
This addresses the critical issue of maintaining anonymous Internet access for Tor users when ISPs block connections, though it is an incremental improvement over existing bridge distribution methods.
The paper tackles the problem of malicious users blocking Tor bridge addresses by proposing TorBricks, a protocol that distributes O(t log(n)) bridges to ensure all honest users can connect to Tor with high probability in O(log(t)) rounds, even when an unknown number t < n of users are adversarial.
Tor is currently the most popular network for anonymous Internet access. It critically relies on volunteer nodes called bridges for relaying Internet traffic when a user's ISP blocks connections to Tor. Unfortunately, current methods for distributing bridges are vulnerable to malicious users who obtain and block bridge addresses. In this paper, we propose TorBricks, a protocol for distributing Tor bridges to n users, even when an unknown number t < n of these users are controlled by a malicious adversary. TorBricks distributes O(tlog(n)) bridges and guarantees that all honest users can connect to Tor with high probability after O(log(t)) rounds of communication with the distributor. We also extend our algorithm to perform privacy-preserving bridge distribution when run among multiple untrusted distributors. This not only prevents the distributors from learning bridge addresses and bridge assignment information, but also provides resistance against malicious attacks from a m/3 fraction of the distributors, where m is the number of distributors.