Efficient Receipt-Free Ballot Casting Resistant to Covert Channels

Open-audit election protocols have, in recent years, focused on the ballot casting process, where the difficulty lies in proving to the unaided voter that the encrypted ballot faithfully captures her intent. We present MarkPledge2, an evolution of Neff’s MarkPledge scheme and the first efficient, covert-channel-resistant, receipt-free ballot casting scheme that can be used by humans without trusted hardware. In comparison to the Moran-Naor proposal at CRYPTO 2006 which shares some of our goals, our scheme produces a significantly shorter ballot, prevents covert channels in the ballot, and opts for statistical soundness rather than everlasting privacy (achieving both seems impossible). The human interface remains the same as MarkPledge, requiring of the voter only very-short-string comparisons. This work solves an “interesting open problem” raised in the original Moran-Naor paper.