Small Coalitions Cannot Manipulate Voting

We demonstrate how to make voting protocols resistant against manipulation by computationally bounded malicious voters, by extending the previous results of Conitzer and Sandholm in several important directions: we use one-way functions to close a security loophole that allowed voting officials to exert disproportionate influence on the outcome and show that our hardness results hold against a large fraction of manipulating voters (rather than a single voter). These improvements address important concerns in the field of secure voting systems. We also discuss the limitations of the current approach, showing that it cannot be used to achieve certain very desirable hardness criteria.