Surtr: Transparent Verification with Simple yet Strong Coercion Mitigation

Transparent verification allows voters to directly identify their vote in cleartext in the final tally result. Both Selene and Hyperion offer this simple and intuitive verification method, and at the same time allow for coercion to be mitigated under the assumption that tally servers can privately notify voters of the keying material needed for verification. Subsequently, a voter can generate fake keying material to deceive a coercer. In this paper, we propose Surtr, a new scheme that enables transparent verification without requiring a private notification channel. This approach strengthens coercion mitigation, since a coercer can monitor the notification channel, and simplifies the process by eliminating the need for voters to generate fake keying material for the coercer.