Receipt-free secret-ballot elections (extended abstract)

Prior verifiable secret-ballot election protocols all suffer from a common defect whkhrenderst hemunsuitablef orpracticalu se: they allow voters to (if they wish) carry away from the protocol receipts which can be used to prove to others how they voted. This simple defect enables vote buying and coercion which are impractical in current physical election systems due to the " plausible deniability " offered by a voting booth. This defect is embedded, not only within prior election protocols, but within all of the more general protocols for collective computation of a public function from private inputs. This paper presents the first verifiable secret-ballot election protocols in which participants are unable to prove to others how they voted. 1 Introduction In traditional elections, the voting booth does more thi~n allow voters to keep their votes private, it actually requires that votes stay secret. This may seem like a subtle distinction, but it is, in fact, an essential component of secret-ballot elections. If a voter is allowed, but not required, to keep a vote secret, the voter could be coerced by an employer or anyone with power over the voter into casting a certain vote. The cryptographic election schemes found in the literature all suffer from a common deficiency. While they may allow a voter to conceal a vote, they also allow a voter to carry away a receipt which can be used to prove to a third party that a particular vote was cast. While thki receipt may seem like a feature, it eliminates the ability of a voter to deceive others about its vote. The additional capabilities given to an individual voter are actually a dlsadv.antage for that voter! * benaloh@crypt.mcs. — supported in pmt by a Clarkson Graduate Trustees' Scholarship. Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association of Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. With voting booths, a voter can make promises to employers, accept bribes, and belong to organizations which are committed to a particular vote. Yet the voter, in the privacy of a voting booth, may cast the opposite vote without fear of repercussions or …