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.
Herbivore scales DC-nets by dividing users into many small anonymity sets @cite_81 . creates a single large anonymity set, and thus enables every client to be anonymous amongst the entire set of honest clients.
@cite_81
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Anonymity is increasingly important for networked applications amidst concerns over censorship and privacy. In this paper, we describe Herbivore, a peer-to-peer, scalable, tamper-resilient communication system that provides provable anonymity and privacy. Building on dining cryptographer networks, Herbivore scales by partitioning the network into anonymizing cliques. Adversaries able to monitor all network traffic cannot deduce the identity of a sender or receiver beyond an anonymizing clique. In addition to strong anonymity, Herbivore simultaneously provides high efficiency and scalability, distinguishing it from other anonymous communication protocols. Performance measurements from a prototype implementation show that the system can achieve high bandwidths and low latencies when deployed over the Internet. Anonymity is increasingly important for networked applications amidst concerns over censorship and privacy. This paper outlines the design of HerbivoreFS, a scalable and efficient file sharing system that provides strong anonymity. HerbivoreFS provides computational guarantees that even adversaries able to monitor all network traffic cannot deduce the identity of a sender or receiver beyond an anonymizing clique of k peers. HerbivoreFS achieves scalability by partitioning the global network into smaller anonymizing cliques. Measurements on PlanetLab indicate that the system achieves high anonymous bandwidth when deployed on the Internet. Users often wish to participate in online groups anonymously, but misbehaving users may abuse this anonymity to disrupt the group's communication. Existing messaging protocols such as DC-nets leave groups vulnerable to denial-of-service and Sybil attacks, Mix-nets are difficult to protect against traffic analysis, and accountable voting protocols are unsuited to general anonymous messaging. We present the first general messaging protocol that offers provable anonymity with accountability for moderate-size groups, and efficiently handles unbalanced loads where few members wish to transmit in a given round. The N group members first cooperatively shuffle an N x N matrix of pseudorandom seeds, then use these seeds in N "pre-planned" DC-nets protocol runs. Each DC-nets run transmits the variable-length bulk data comprising one member's message, using the minimum number of bits required for anonymity under our attack model. The protocol preserves message integrity and one-to-one correspondence between members and messages, makes denial-of-service attacks by members traceable to the culprit, and efficiently handles large, unbalanced message loads. A working prototype demonstrates the protocol's practicality for anonymous messaging in groups of 40+ members. Among anonymity systems, DC-nets have long held attraction for their resistance to traffic analysis attacks, but practical implementations remain vulnerable to internal disruption or "jamming" attacks, which require time-consuming detection procedures to resolve. We present Verdict, the first practical anonymous group communication system built using proactively verifiable DC-nets: participants use public-key cryptography to construct DC-net ciphertexts, and use zero-knowledge proofs of knowledge to detect and exclude misbehavior before disruption. We compare three alternative constructions for verifiable DC-nets: one using bilinear maps and two based on simpler ElGamal encryption. While verifiable DC-nets incur higher computational overheads due to the public-key cryptography involved, our experiments suggest that Verdict is practical for anonymous group messaging or microblogging applications, supporting groups of 100 clients at 1 second per round or 1000 clients at 10 seconds per round. Furthermore, we show how existing symmetric-key DC-nets can "fall back" to a verifiable DC-net to quickly identify misbehavior, speeding up previous detections schemes by two orders of magnitude.