On the anonymity of privacy-preserving many-to-many communication in the presence of node churn and attacks

Anonymity can protect from political repression in Online Social Networks (OSNs) as well as from undesired profiling, e.g., by advertisement companies, in todays' Internet. P2P-based anonymous publish-subscribe (pub-sub) is a highly-scalable approach to protect anonymity while enabling efficient many-to-many communication between services and users. However, churn and the resulting overlay degradation in P2P-based pub-sub systems require repairs and optimizations to maintain anonymity and efficiency. This paper analyzes attacks on such repair and optimization functions to disclose participants. For that, we apply a strong attacker model that combines large-scale traffic monitoring with malicious insiders. Furthermore, we propose and evaluate heuristic countermeasures. Our findings indicate that some attacks can be mitigated at reasonable costs. However, churn seems to remain a major threat to anonymity.