This paper addresses the problem of constructing voting protocols that are hard to manipulate. We describe a general technique for obtaining a new protocol by combining two or more base protocols, and study the resulting class of (vote-once) hybrid voting protocols, which also includes most previously known manipulationresistant protocols. We show that for many choices of underlying base protocols, including some that are easily manipulable, their hybrids are NP-hard to manipulate, and demonstrate that this method can be used to produce manipulationresistant protocols with unique combinations of useful features. 1

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 o#cials 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.