Paper 2004/355

A Small-Scale Voting Protocol Hiding Vote-Counts of All Candidates

Pei-yih Ting and Po-Yueh Hung

Abstract

In this paper, we focus on the design of the winner-determination procedure of an electronic voting protocol used at critical elections, e.g. at the meeting of the board of a company for critical business decisions or a parliamentary committee for legislation. The number of participating voters is limited to several hundreds but the voting should satisfy a new privacy requirement that the accumulated vote-counts of all candidates should be kept as secret as possible. This additional requirement is significant only for small/medium-scale elections. Traditional electronic voting frameworks simply take the announcement of vote-counts for granted and hope that each individual¡¦s actual vote is hidden in the accumulated vote-counts. Therefore, it is not easy to modify an existing scheme to approach this new goal. In the proposed protocol, the homomorphic ElGamal cryptosystem is used. An electronic bulletin board holds public announced values. A ballot consists of separate encrypted ¡¥yes¡¦/¡¦no¡¦ vote for each candidate such that the accumulated vote-counts can be calculated from the ciphertexts without any decryption. The correctness of each ballot is guaranteed through ZKPs. The accumulated vote-count ciphertexts are then converted to encrypted unary representation through a mix-and-match sub-protocol such that the vote-counts can be concealed in the winner-determination stage. This protocol is suited for both equal-voting and weighted-voting schemes. Also, the type of voter¡¦s selection can be single choice, multiple choices, ranking choice, or the allocative choice.