Cryptology ePrint Archive: Report 2015/942
Secrecy and independence for election schemes
Abstract: We study ballot secrecy and ballot independence for election schemes.
First, we propose a definition of ballot secrecy
as an indistinguishability game in the computational model of cryptography.
Our definition builds upon and strengthens earlier
to ensure that ballot secrecy is preserved in the
presence of an adversary that controls
the bulletin board and communication channel.
Secondly, we propose a definition of ballot independence as an adaptation of
a non-malleability definition for asymmetric encryption. We also provide
a simpler, equivalent definition as an indistinguishability game.
Thirdly, we prove relations between our definitions. In particular, we prove
that ballot independence is necessary in election schemes satisfying ballot secrecy.
And that ballot independence is sufficient for ballot secrecy in
election schemes with zero-knowledge tallying proofs.
Fourthly, we demonstrate the applicability of our results by
analysing Helios. Our analysis identifies a new attack against
Helios, which enables an adversary to determine if a voter did not
vote for a candidate chosen by the adversary.
The attack requires the adversary to control the bulletin board or communication channel,
thus, it could not have been detected by earlier definitions of
Finally, we prove that ballot secrecy is satisfied by a variant of
Helios that uses non-malleable ballots.
Category / Keywords: foundations / anonymity, election schemes, foundations, Helios, independence, non-malleability, privacy, public-key cryptography, secrecy, voting
Date: received 26 Sep 2015, last revised 28 Dec 2016
Contact author: research at bensmyth com
Available format(s): PDF | BibTeX Citation
Version: 20161228:181001 (All versions of this report)
Short URL: ia.cr/2015/942
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