A novel protocol to allow revocation of votes a hybrid voting system

A hybrid voting system allows voters to revoke their electronic vote at the polling station. This approach is meant to provide full individual and universal verifiability without introducing the threats of vote buying or voter coercion. Such an integration of traditional and electronic voting systems requires the voters´ ability to prove whether they have already voted electronically, and if so, to show which of all the electronic votes published on the public bulletin board is theirs. This paper proposes in full cryptographic detail a novel e-voting protocol that allows voters to unambiguously show and prove to voting officials at the polling station if they have cast an electronic vote. If this is the case, the voters can use their secret credentials to locate their votes on the public bulletin board without giving up the secrecy of the credentials. Remarkably, our protocol enables them to do so, even if their votes have been cast by a third party that got hold of their credentials. We thus address the hardest possible attack on a voter´s right to vote. Furthermore, unlike pure e-voting systems, our protocol allows the hybrid system to provide coercion-resistance even when voters are allowed to vote for write-in candidates. Our approach is meant to appeal to governments that aim at offering voters the choice between two channels for casting votes, rather than fully replacing their traditional paper-based voting scheme with an e-voting system.