D4.1 - Security definitions and attacker models for e-voting protocols

In 2010 Hao, Ryan and Zielinski proposed a simple decentralized e-voting protocol that only requires 2 rounds of communication. Thus, for k elections their protocol needs 2k rounds of communication. Observing that the first round of their protocol is aimed to establish the public-keys of the voters, we propose an extension of the protocol as a non-interactive e-voting scheme in the public-key setting (NIVS) in which the voters, after having published their public-keys, can use the corresponding secret-keys to participate in an arbitrary number of one-round elections. We first construct a NIVS with a standard tally function where the number of votes for each candidate is counted. Further, we present constructions for two alternative types of elections. Specifically in the first type (dead or alive elections) the tally shows if at least one voter cast a vote for the candidate. In the second one (elections by unanimity), the tally shows if all voters cast a vote for the candidate. Our constructions are based on bilinear groups of prime order. As definitional contribution we provide formal computational definitions for privacy and verifiability of NIVSs. We conclude by showing intriguing relations between our results, secure computation, electronic exams and conference management systems.