Implementing STV Securely in Prêt à Voter

Abstract

Work on electronic voting systems to date has largely focused around first-past-the-post voting. However, the governments of many countries, and many non-governmental organisations, use a single transferable vote system, in which the voter needs to indicate not just a single preferred candidate but a preference ranking of (some or all of) the candidates on offer. This paper investigates the possibility of modifying Prˆet `a Voter to cope with a single transferable vote system. With its newer form involving re-encryption mixes [8], this seems at first sight to be impossible; with the older version based on RSA onions [2], the obvious approach works, but security is less than ideal; using multiple re-encryption mix onions for each vote, combined with a lazy decryption semantics, however, proves to be an elegant and efficient solution to the problem.

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