Séminaire de Cryptographie

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Quentin Santos

Practical Strategy-Resistant Privacy-Preserving Elections

Recent advances in cryptography promise to let us run com- plex algorithms in the encrypted domain. However, these results are still mostly theoretical since the running times are still much larger than their equivalents in the plaintext domain. In this context, Majority Judgment is a recent proposal for a new voting system with several interesting practical advantages, but which implies a more involved tallying process than rst-past-the-post voting. To protect voters' privacy, such a process needs to be done by only manipulating encrypted data. In this paper, we then explore the possibility of computing the (ordered) winners in the Majority Judgment election without leaking any other in- formation, using homomorphic encryption and multiparty computation. We particularly focus on the practicality of such a solution and, for this purpose, we optimize both the algorithms and the implementations of several cryptographic building blocks. Our result is very positive, show- ing that this is as of now possible to attain practical running times for such a complex privacy-protecting tallying process, even for large-scale elections.