CRCS Privacy and Security Lunch Seminar

Date: Wednesday, March 4, 2009
Time: 12:00pm-1:30 pm
Place: Maxwell Dworkin 119

Speaker: Tal Moran (CRCS Harvard)

Title: Shuffle-Sum: Coercion-Resistant Verifiable Tallying for STV Voting

Abstract: There are many advantages to voting schemes in which voters rank all candidates in order, rather than just choosing their favorite. However, these schemes inherently suffer from a coercion problem when there are many candidates, because a coercer can demand a certain permutation from a voter and then check whether that permutation appears during tallying.Recently developed cryptographic voting protocols allow anyone to audit an election (universal verifiability), but existing systems are either not applicable to ranked voting at all, or reveal enough information about the ballots to make voter coercion possible.

We solve this problem for the popular single transferable vote (STV) ranked voting system (used in Australia, Ireland, Malta and in Cambridge, MA, among others), by constructing an algorithm for the verifiable tallying of encrypted votes. In the talk I will describe this algorithm, along with all the necessary background about cryptographically verifiable elections, the STV voting system and voter coercion problems.

Bio: Tal Moran is interested in employing ideas and techniques from theoretical cryptography to design secure systems in the “real world”. Two examples, from Tal’s PhD thesis, are simple protocols for polling sensitive questions that maintain privacy for the responder (using physical envelopes or scratch-off cards), and protocols for human-verifiable, secure elections. These are backed by formal definitions and proofs, making the security assumptions and guarantees explicit, and implementations easier to verify. Tal completed his PhD at the Weizmann Institute of Science, under the supervision of Moni Naor, and his undergraduate and master’s degrees at Tel-Aviv University.