Cryptology ePrint Archive: Report 2018/017

Verifiability of Helios Mixnet

Ben Smyth

Abstract: We study game-based definitions of individual and universal verifiability by Smyth, Frink & Clarkson. We prove that building voting systems from El Gamal coupled with proofs of correct key generation suffices for individual verifiability. We also prove that it suffices for an aspect of universal verifiability. Thereby eliminating the expense of individual-verifiability proofs and simplifying universal-verifiability proofs for a class of encryption-based voting systems. We use the definitions of individual and universal verifiability to analyse the mixnet variant of Helios. Our analysis reveals that universal verifiability is not satisfied by implementations using the weak Fiat-Shamir transformation. Moreover, we prove that individual and universal verifiability are satisfied when statements are included in hashes (i.e., when using the Fiat-Shamir transformation, rather than the weak Fiat-Shamir transformation).

Category / Keywords: cryptographic protocols / election schemes, verifiability

Original Publication (with major differences): Voting'18: 3rd Workshop on Advances in Secure Electronic Voting

Date: received 4 Jan 2018, last revised 11 Mar 2018

Contact author: research at bensmyth com

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Version: 20180311:161207 (All versions of this report)

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