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Abstract
Conducting elections in Australia has unique challenges arising from the country's geographical dispersion and the widespread use of many varieties of preferential electoral systems. Online and electronic election systems can be of great benefit in addressing many of these problems, and indeed many such systems are currently in use or at least being considered. However online and electronic elections magnify and change the nature of many of the security risks already present in manual elections. Furthermore in contrast to the more simple electoral systems used elsewhere, Australia's complex preferential systems are inherently susceptible to voter coercion through covert signature attacks during the counting.
In this thesis we identify existing security vulnerabilities in Australian elections, and we propose cryptographic online election schemes that mitigate many of these risks. The thesis is divided into three parts. In Part I we examine practical problems and security risks in current manual and electronic election procedures in Australia. In particular we describe errors in current Australian legislation for preferential counting and flaws in the counting software. Then in Part II we review contemporary cryptographic approaches for mitigating security risks in online elections. We discuss drawbacks of existing cryptographic solutions that make them unsuitable for practical online elections in Australia.
In Part III we present new cryptographic schemes for online elections. First we propose an online voting scheme that prevents coercion during the voting under weaker communication assumptions than previous schemes. Then we introduce several online counting schemes for preferential systems commonly used in Australia. Our preferential counting schemes provide the maximum possible protection against signature attacks and any other potential covert counting attacks. In developing these counting schemes, we introduce a novel way of applying software engineering design techniques to the cryptographic setting. These design techniques help ensure that the schemes correctly implement the complex preferential counting algorithms without inadvertently leaking information. Our techniques have wider relevance to developing cryptographic protocols for complex applications.