Mental voting booths

In this paper, we introduce the notion of mental voting booths, i.e., a building block for voting schemes that provides remote voters with similar protection as that offered by physical voting booths, essentially protecting them from over-the-shoulder coercion attacks (shoulder-surfing). We introduce a framework to model voting booths and formulate a property of the modelled booths that is sufficient to ensure over-the-shoulder coercion resistance. Next, we propose an example of mental booth that is simple enough to be used by any voter without prior training and show that an execution of the remote booth in the presence of the adversary is equivalent to that execution in his absence (e.g., inside a physical booth). The only cost lies in the use of an untappable channel in order to transmit a piece of information before the voting phase. Mental booths also allow for the voter to safely delegate his own voice to an untrusted person while still being able to verify that the untrusted person followed his instructions while voting.