  This paper presents Riposte, a new system for anonymous broadcast messaging.
Riposte is the first such system, to our knowledge, that simultaneously
protects against traffic-analysis attacks, prevents anonymous denial-of-service
by malicious clients, and scales to million-user anonymity sets. To achieve
these properties, Riposte makes novel use of techniques used in systems for
private information retrieval and secure multi-party computation. For
latency-tolerant workloads with many more readers than writers (e.g. Twitter,
Wikileaks), we demonstrate that a three-server Riposte cluster can build an
anonymity set of 2,895,216 users in 32 hours.
