Paper 2024/1182 Original: eprint.iacr.org/2024/1182 ↗

Hyperion: Transparent End-to-End Verifiable Voting with Coercion Mitigation

Abstract

We present Hyperion, an end-to-end verifiable e-voting scheme that allows the voters to identify their votes in cleartext in the final tally. In contrast to schemes like Selene or sElect, identification is not via (private) tracker numbers but via cryptographic commitment terms. After publishing the tally, the Election Authority provides each voter with an individual dual key. Voters identify their votes by raising their dual key to their secret trapdoor key and finding the matching commitment term in the tally. The dual keys are self-certifying in that, without the voter's trapdoor key, it is intractable to forge a dual key that, when raised to the trapdoor key, will match an alternative commitment. On the other hand, a voter can use their own trapdoor key to forge a dual key to fool any would-be coercer. Additionally, we propose a variant of Hyperion that counters the tracker collision threat present in Selene. We introduce individual verifiable views: each voter gets their own independently shuffled view of the master Bulletin Board. We provide new improved definitions of privacy and verifiability for e-voting schemes and prove the scheme secure against these, as well as proving security with respect to earlier definitions in the literature. Finally, we provide a prototype implementation and provide measurements which demonstrate that our scheme is practical for large scale elections.