The bribery problem in election has received considerable attention in the
literature, upon which various algorithmic and complexity results have been
obtained. It is thus natural to ask whether we can protect an election from
potential bribery. We assume that the protector can protect a voter with some
cost (e.g., by isolating the voter from potential bribers). A protected voter
cannot be bribed. Under this setting, we consider the following bi-level
decision problem: Is it possible for the protector to protect a proper subset
of voters such that no briber with a fixed budget on bribery can alter the
election result? The goal of this paper is to give a full picture on the
complexity of protection problems. We give an extensive study on the protection
problem and provide algorithmic and complexity results. Comparing our results
with that on the bribery problems, we observe that the protection problem is in
general significantly harder. Indeed, it becomes ∑p2-complete even for
very restricted special cases, while most bribery problems lie in NP. However,
it is not necessarily the case that the protection problem is always harder.
Some of the protection problems can still be solved in polynomial time, while
some of them remain as hard as the bribery problem under the same setting.Comment: 28 Pages. The Article has been accepted in the 26th International
Computing and Combinatorics Conference (COCOON 2020