TorBricks: Blocking-Resistant Tor Bridge Distribution

TL;DR

TorBricks introduces a robust protocol for distributing Tor bridges that resists malicious users and preserves privacy, ensuring reliable anonymous access even under adversarial conditions.

Contribution

The paper presents a novel, scalable protocol for distributing Tor bridges resistant to malicious users and capable of privacy-preserving multi-distributor deployment.

Findings

Distributes O(t log n) bridges to resist malicious users

Guarantees high probability of connection after O(log t) rounds

Supports privacy-preserving distribution among multiple untrusted distributors

Abstract

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.