Security Analysis of Accountable Anonymous Group Communication in Dissent
YALE UNIV NEW HAVEN CT DEPT OF COMPUTER SCIENCE
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Users often wish to communicate anonymously on the Internet using, for instance, group discussion forums or instant messaging. Misbehaving users may abuse this anonymity to disrupt communication, however, and existing solutions do not adequately address this risk. Messaging protocols such as DC-nets leave groups vulnerable to denial-of-service and Sybil attacks, mixnets are difficult to protect against traffic analysis, and accountable voting protocols are unsuited to general anonymous messaging. DISSENT, originally introduced by Corrigan-Gibbs and Ford 2010, is the first general communication protocol that offers provable anonymity, integrity and accountability for moderatesize groups, and efficiently handles unbalanced loads where few members wish to transmit in a given round. We provide a full description of an improved DISSENT protocol, define its precise security properties, and give rigorous proofs of these properties. Our improved protocol is a direct result of this security analysis, which identified several non-trivial attacks on the original protocol stemming from subtle design flaws.