Thomas Haines

Eleanor McMurtry, Xavier Boyen, Chris Culnane et al.

We propose a protocol for verifiable remote voting with paper assurance. It is intended to augment existing postal voting procedures, allowing a ballot to be electronically constructed, printed on paper, then returned in the post. It allows each voter to verify that their vote has been correctly cast, recorded and tallied by the Electoral Commission. The system is not end-to-end verifiable, but does allow voters to detect manipulation by an adversary who controls either the voting device, or (the postal service and electoral commission) but not both. The protocol is not receipt-free, but if the client honestly follows the protocol (including possibly remembering everything), they cannot subsequently prove how they voted. Our proposal is the first to combine plain paper assurance with cryptographic verification in a (passively) receipt-free manner.

Thomas Haines

In this paper, we describe an optimised variant of Wikström's mixnet which shuffles vectors of ElGamal ciphertexts in parallel. We then show in detail that this construction is secure. Wikström's verifiable mixnet as we refer to it here was first presented in "Proofs of Restricted Shuffles" by Terelius and Wikström, building on Wikström's previous work. Specifically we take the optimised variant for ElGamal which appears to be in common use; for instance, it is presented in Haenni et al's "Pseudo-Code Algorithms for Verifiable Re-Encryption Mix-Nets". We extend the mixnet to support parallel shuffles. (The possibility of doing this is proven by the Wikström's result but we wish to show that this particular instance with its optimisations is secure.)