Cobra: Toward Concurrent Ballot Authorization for Internet Voting

We propose and study the notion of concurrent ballot authorization for coercion-resistant, end-to-end verifiable (E2E) internet voting. A central part of providing coercion resistance is the ability for an election authority to filter out fake ballots from legitimate ones in a way that is both private and universally verifiable. This ballot authorization process, however, can potentially come at a heavy computational cost. In previous proposals, the bulk of this computation cannot be performed until the last ballot has been cast. By contrast, concurrent ballot authorization allows ballots to be authorized as they are submitted, allowing the tally to be declared immediately after polls close. An efficient tally is especially important in the coercion-resistant internet voting setting, as it is particularly vulnerable to denial of service attacks caused by floods of fake ballots. We present a proof-of-concept voting system, Cobra, the first coercion-resistant system to offer concurrent ballot authorization. Although Cobra offers the fastest tallying relative to the related work, it has a registration process that we consider to be too slow to be viable; one that is quadratic in the number of eligible voters. We present Cobra as a first-step toward what we hope will become a standard feature of coercion-resistant internet voting schemes: concurrent ballot authorization.