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 insurance 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 overlay degradation in P2P-based pub-sub systems require periodic repair and optimization operations to maintain the anonymity protection and the efficiency of the content dissemination. This paper analyzes attacks on such repair and optimization functions to disclose publishers and subscribers. 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