Abstract:
Fair conduct of elections are essential for smooth existence of democratic societies. Voting
systems are the method and infrastructure we use to conduct elections. Paper ballot based
voting schemes, electronic voting machines based schemes, etc., are the some of the traditional
voting schemes. These schemes full lls most of the basic requirements, and simplicity of these
schemes makes them attractive even today. But there have a major drawback for these schemes,
that is, for a voter it is nearly impossible to verify the correctness of election results. Voters
left with no choice other than trusting on election administrators and party representatives for
the correctness of election result. To address this issue, researchers come up with end to end
veri able voting schemes, where voter can verify that her vote is cast-as-intended, recorded-as-
cast and counted-as-recorded, and anybody can verify correctness of each and every step, all the
while preserving voter privacy. From the last three decades, researchers have proposed many
such schemes, many of them make use of mixnet for anonymization. P^ret a voter, Helios are
the example for such mixnet based voting schemes. Here the mixnet work as a black box, and
used for removing the mapping between voters and the encrypted votes. In the voting schemes
case, mixnet receives a set of encrypted votes as input and output another set of ciphertexts.
This makes proof of integrity is essential, to ensure that mixnet haven't added or removed any
vote ciphertext. In this dissertation, we propose two new schemes, both of them follows same
structure of Helios but facilitate new ways for proof of mixnet integrity. The idea of rst one is
based on adding tweak values in ElGamal ciphertext. And the second one make use of dummy
votes to provide proof of mixnet integrity. While the tweak based scheme is only applicable to
ElGamal encryption scheme based mixnets, the dummy vote based idea can be extended for
proof of integrity in any other mixnet based schemes.
