Paper 2025/1625

A Practical and Fully Distributed E-Voting Protocol for the Swiss Context

Abstract

Internet voting in Switzerland for political elections is strongly regulated by the Federal Chancellery (FCh). It puts a great emphasis on the individual verifiability: security against a corrupted voting device is ensured via return codes, sent by postal mail. For a long time, the FCh was accepting to trust an offline component to set up data and in particular the voting material. Today, the FCh aims at removing this strong trust assumption. We propose a protocol that abides by this new will. At the heart of our system lies a setup phase where several parties create the voting material in a distributed way, while allowing one of the parties to remain offline during the voting phase. A complication arises from the fact that the voting material has to be printed, sent by postal mail, and then used by the voter to perform several operations that are critical for security. Usability constraints are taken into account in our design, both in terms of computation complexity (linear setup and tally) and in terms of user experience (we ask the voter to type a high-entropy string only once). The security of our scheme is proved in a symbolic setting, using the ProVerif prover, for various corruption scenarios, demonstrating that it fulfills the Chancellery’s requirements and sometimes goes slightly beyond them.