Two Cents for Strong Anonymity: The Anonymous Post-office Protocol

We introduce the Anonymous Post-office Protocol (AnonPoP), a practical strongly-anonymous messaging system. AnonPoP offers anonymity against globally eavesdropping adversaries that control a majority of AnonPoP’s servers. AnonPoP design combines effectively known techniques such as (synchronous) mixcascade and constant sending rate, with several new techniques including request-pool, bad-server isolation and per-epoch mailboxes. AnonPoP is affordable, with monthly costs of 2¢ per client, and efficient with respect to latency, communication, and energy, making it suitable for mobile clients. We developed an API that allows other applications to use AnonPoP for adding strong anonymity. We validated the system and its usability by experiments in cloud-based deployment and simulations, including a POC Android messaging application and a ‘doubleblinded’ usability study.