Applying Divertibility to Blind Ballot Copying in the Helios Internet Voting System

Cortier & Smyth have explored ballot copying in the Helios e-voting platform as an attack against privacy. They also pointed out that their approach to ballot copying could be detected by a modified Helios. We revisit ballot copying from a different viewpoint: as a tool to prevent vote diffusion (the division of votes among multiple weak candidates) and to lessen the effect of established voting blocs. Our approach is based on blinding the ballot casting protocol to create an undetectable copy. A willing voter can cooperate with a prospective copier, helping the copier produce a blinded copy of his ballot without revealing his vote. We prove that Helios is unable to detect the copying. The possibility of such cooperation between voters is manifested only in internet voting and as such is a fundamental difference between internet and booth voting.

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