Many of us have dealt with electronic commerce transactions. This is already a part of everyday life. However, e-voting is not yet an obvious method for voting. The construction of electronic voting system is one of the most challenging security-critical tasks, because of the need for finding a trade-off between many seemingly contradictory security requirements like privacy vs. auditability. Thereby it is difficult to adopt ordinary mechanisms of e-commerce. For example, in e-commerce there is always a possibility to dispute about the content of transactions. Buyers get receipts to prove their participation in transactions. E-voters, in turn, must not get any receipts, because this would enable voters to sell their votes.
In 2003, Estonia initiated the project of e-voting. The aim was to implement e-voting in the elections of the local government councils in 2005. In January 2004, a group of American security experts revealed the security report of Secure Electronic Registration and Voting Experiment (SERVE) . The SERVE system was planned for deployment in the 2004 primary and general elections and allows eligible voters to vote electronically via Internet. After examining the security of SERVE, the group of security experts recommended that SERVE should be shut down. They also declared that they do not believe that differently constituted projects could be more secure than SERVE. Their conclusion was that the real barriers to success in e-voting are not skills, resources, etc; it is the fact that given the current Internet and PC security technology, e-voting is an essentially impossible task.
The SERVE project was terminated indeed in January 2004. At the same time, Estonia continued to develop an e-voting system and implemented it according to the plans. The Estonian security experts published their security analysis  at the end of 2003. They declared that in practical sense the Estonian e-voting system is secure enough for implementation.
This contradicting situation was the main initiator of this work. By closer view, both security reports are consistent and contain truthful and convincing arguments. One of the main reasons for two totally different results was the lack of unified rational security analysis in both reports. Some of the arguments were quite emotional, being based on experts’ subjective opinions and “common wisdom”.
The aim of the work is to adapt rational security analysis methods for studying the two evoting systems. It gives us the possibility to compare the practical security of these systems.
In absolutely secure systems unexpected events are not possible. We may dream about such systems, but they can never be achieved in practice. This applies particularly to evoting systems. Considering the security level of personal computers, it is impossible to design e-voting systems, which are absolutely secure for every user. The most important security goal of voting is not to affect the final results and not to abuse the principles of10 democracy. The single incidents with users are still important but they do not have influence to the final result. Moreover, even in traditional voting systems small-scale incidents are acceptable. Therefore, in practical security analysis of e-voting we should concentrate on large-scale threats.
One of the rational approaches of security is known from theoretical cryptography: security reductions, which are proofs that security conditions held under certain combinatorial assumptions, such as hardness of factoring or Diffie-Hellman problem. For proving practical security, we also need empirical assumptions about the real world. Moreover, in theoretical cryptography the adversaries are considered to be Turing machines, which are well-defined and relatively easy to study. The real world adversaries are human beings with unpredictable behavior and different motives. Hence, for analyzing practical security, we need real world adversary models. There...