D-Shuffle for Pret a Voter

摘要

Pret a Voter is an end-to-end verifiable voting scheme, that uses paper based ballot forms that are turned into encrypted receipts. The scheme was designed to be flexible, secure and to offer voters a familiar and easy voting experience. Secrecy of the vote in Pret a Voter relies on encoding the vote using a randomized candidate list in the ballots. In a few variants of Pret a Voter a verifiable shuffle was used in the ballot generation phase in order to randomize the candidates. Verifiable shuffles are cryptographic primitives that re-encrypt and permute a list of ciphertexts. They provide proofs of correctness of the shuffle and preserve secrecy of the permutation. This paper proposes a new verifiable shuffle "D-Shuffle" that is efficient. We provide a security proof for the D-Shuffle. Furthermore, we show that using the D-shuffle for generating ballots in Pret a Voter scheme ensures its security against: "Authority Knowledge Attack" and "Chain of Custody Attack".