On verifiable internet voting systems

Thesis Type: Doctorate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Institute of Applied Mathematics, Cryptography, Turkey

Approval Date: 2016


Supervisor: MURAT CENK


After the Estonian Parliamentary Elections held in 2011, an additional verification mechanism was integrated into the i-voting system in order to resist malicious voting devices, including the so-called Student’s Attack. This mechanism gives voters the opportunitytoverifywhetherthevotetheycastisstoredinthecentralsystemcorrectly. However, the verification phase ends by displaying the cast vote in plain form on the verification device. Indeed, when applied in wide range, this would even compromise the fairness and the overall secrecy of the elections. In this work, our aim is to investigate this verification phase in detail and to point out that displaying the cast vote in plain form may leak voter privacy. In this respect, we propose an alternative verification mechanism for the Estonian i-voting system to overcome this vulnerability. Not only is the proposed mechanism secure and resistant against corrupted verification devices, so does it successfully verify whether the vote is correctly stored in the system. We also highlight that our proposed mechanism brings only symmetric encryptions and hash functions on the verification device, thereby mitigating these weaknesses in an efficient way. More concretely, it brings only m additional symmetric key decryptions to the verification device, with m denoting the number of candidates. Finally, we prove the security of the proposed verification mechanism and compare the cost complexity of the proposed method with that of the current mechanism.