Sophisticated Attacks on Decoy Ballots: The Devil's Menu and the Market for Lemons

TL;DR

This paper uses a game-theoretical model to demonstrate that decoy ballots may fail to protect against adversaries, who can exploit a 'Devil's Menu' pricing strategy to buy real ballots, revealing limitations of decoy ballots in elections.

Contribution

It introduces a novel game-theoretical framework showing how adversaries can effectively bypass decoy ballots using a 'Devil's Menu' pricing strategy, challenging their assumed security.

Findings

Adversaries can buy real ballots at targeted prices using the Devil's Menu.

Decoy ballots may be ineffective against strategic adversaries with sufficient budget.

The model applies to both election security and the 'Lemons Problem' in markets.

Abstract

Decoy ballots do not count in election outcomes, but otherwise they are indistinguishable from real ballots. By means of a game-theoretical model, we show that decoy ballots may not provide effective protection against a malevolent adversary trying to buy real ballots. If the citizenry is divided into subgroups (or districts), the adversary can construct a so-called "Devil's Menu" consisting of several prices. In equilibrium, the adversary can buy the real ballots of any strict subset of districts at a price corresponding to the willingness to sell on the part of the citizens holding such ballots. By contrast, decoy voters are trapped into selling their ballots at a low, or even negligible, price. Blowing up the adversary's budget by introducing decoy ballots may thus turn out to be futile. The Devil's Menu can also be applied to the well-known "Lemons Problem".