Countering Ballot Stuffing and Incorporating Eligibility Verifiability in Helios

Helios is a web-based end-to-end verifiable electronic voting system which has been said to be suitable for low-coercion environments. Although many Internet voting schemes have been proposed in the literature, Helios stands out for its real world relevance. It has been used in a number of elections in university campuses around the world and it has also been used recently by the IACR to elect its board members. It was noted that a dishonest server in Helios can stuff ballots and this seems to limit the claims of end-to-end verifiability of the system. In this work, we investigate how the issue of ballot stuffing can be addressed with minimum change to the current vote casting experience in Helios and we argue formally about the security of our techniques. Our ideas are intuitive and general enough to be applied in the context of other Internet voting scheme and they also address recent attacks exploiting the malleability of ballots in Helios.