Individual verifiability in electronic voting

This PhD Thesis is the fruit of the job of the author as a researcher at Scytl Secure Electronic Voting, as well as the collaboration with Paz Morillo, from the Department of Applied Mathematics at UPC and Alex Escala, PhD student. In her job at Scytl, the author has participated in several electronic voting projects for national-level binding elections in different countries. The participation of the author covered from the protocol design phase, to the implementation phase by providing support to the development teams. The thesis focuses on studying the mechanisms that can be provided to the voters, in order to examine and verify the processes executed in a remote electronic voting system. This work has been done as part of the tasks of the author at the electronic voting company Scytl. Although this thesis does not talk about system implementations, which are interesting by themselves, it is indeed focused on protocols which have had, or may have, an application in the real world. Therefore, it may surprise the reader by not using state of the art cryptography such as pairings or lattices, which still, although providing very interesting properties, cannot be efficiently implemented and used in a real system. Otherwise, the protocols presented in this thesis use standard and well-known cryptographic primitives, while providing new functionalities that can be applied in nowadays electronic voting systems. The thesis has the following contents: A survey on electronic voting systems which provide voter verification functionalities. Among these systems we can find the one used in the Municipal and Parliamentary Norwegian elections of 2011 and 2013, and the system used in the Australian State of New South Wales for the General State Elections in 2015, in which the author has had an active participation in the design of their electronic voting protocols. A syntax which can be used for modeling electronic voting systems providing voter verifiability. This syntax is focused on systems characterized by the voter confirming the casting of her vote, after verifying some evidences provided by the protocol. Along with this syntax, definitions for the security properties required for such schemes are provided. A description of the electronic voting protocol and system which has been used in 2014 and 2015 elections in the Swiss Canton of Neuchâtel, which has individual verification functionalities, is also provided in this thesis, together with a formal analysis of th