Pret a Voter with Re-encryption Mixes

Abstract

We present a number of enhancements to the voter veriable election scheme Pr^et a Voter [CRS05]. Firstly, we propose a mechanism for the distributed construction by a set of independent clerks of the ballot forms. This construction leads to proto-ballot forms with the candidate list encrypted and ensures that only a collusion of all the clerks could determine the cryptographic seeds or the onion/candidate list association. This eliminates the need to trust a single authority to keep this information secret. Furthermore, it allows the on-demand decryption and printing of the ballot forms, so eliminating chain of custody issues and the chain voting style attacks against encrypted receipt schemes identified in [RP05]. The ballot forms proposed here use ElGamal randomised encryption so enabling the use of re-encryption mixes for the anonymising tabulation phase in place of the decryption mixes. This has a number of advantages over the RSA decryption mixes used previously: tolerance against failure of any of the mix tellers, full mixing of terms over the Z*p space and enabling the mixes and audits to be fully independently rerun if necessary.

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