Congratulations to Zhe Xia for successfully passing his PhD viva

Monday 29 June 2009

Election systems have played an important role in human democracy for thousands of years. In traditional election systems, all received votes are tallied manually. For large scale elections, this method is not only inefficient, but also it is error prone and hard to provide a completely accurate result. Sometimes, several recounts will give different results. An initial motivation for introducing mechanical or electronic support has been to provide efficient tallying and cost reduction. Although voting equipment, e.g. lever machines or DRE machines, can be designed under very strict standards, or independently verified by third parties, their internal workings are still hidden when they are implemented in an election. Thus, voters have to trust that the system will correctly tally the election. However, recent high-profile reports have exposed that some such equipment in fact suffers from a variety of security flaws.

In recent years, thanks to the improvement of cryptographic techniques, researchers have found some mathematical solutions to design secure election systems, in which security is the key feature: the correct behaviour of these systems can be verified publicly, without the loss of voter privacy. As a result, voters can themselves verify that their votes have been correctly counted instead of trusting the provided equipment or election officials. The research in this area has made a lot of steady progress. To date, several protocols already have been presented and implemented, for example, Prêt a Voter, Punchscan and VoteHere. This thesis contributes to the work on secure electronic voting systems, especially those related to the Prêt a Voter suite of protocols:

• Firstly, the thesis classifies and summarises the cryptographic building blocks which are relevant to the secure e-voting research. Also it illustrates how these building blocks can be implemented to generate secure e-voting protocols using different strategies, e.g. additive homomorphic encryption and mix networks. Furthermore, it reviews and analyses several latest voter verifiable election systems which are not only achieving high level of security standard but also practical for ordinary voters.
• Secondly, this thesis introduces a number of contributions extending the design of the Prêt a Voter protocols.
• Last but not least, this thesis has introduced some threat analysis of two existing voter verifiable election systems. It has revealed a number of security flaws within these two systems which were not previous known.