Verifiability and receipt-freeness in cryptographic voting systems

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Tezin Türü: Doktora

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Edebiyat Fakültesi, Matematik Bölümü, Türkiye

Tezin Onay Tarihi: 2007

Öğrenci: ORHAN ÇETİNKAYA

Danışman: ALİ DOĞANAKSOY

Özet:

This thesis examines verifiability and receipt freeness in cryptographic voting protocols in detail and points out the contradiction between these requirements. Firstly, an extensive electronic voting requirement set is clearly defined, and then the voting dilemma is described. This is followed by a suggestion of an applicable solution to overcome the voting dilemma by introducing Predefined Fake Vote (PreFote) scheme. Based on a comprehensive literature review, a classification of the existing privacy preserving approaches and a taxonomy of the existing cryptographic voting protocols extending the previous studies are provided. Thereby, a complete and secure cryptographic voting protocol satisfying all electronic voting security requirements at the same time seems non-existent. Hence, an alternative privacy preserving approach is highly needed. Pseudo-Voter Identity (PVID) scheme, proposed in the present study, is a practical and low cost one. The PVID scheme is based on RSA blind signature, and it allows recasting without sacrificing uniqueness. Furthermore, this study proposes a dynamic ballot mechanism including an extension with PreFotes. This study, wherein the PVID scheme and extended dynamic ballots with PreFotes are employed, proposes a practical, complete and secure cryptographic voting protocol over a network for large scale elections, which fulfils all of the electronic voting security requirements: privacy, eligibility, uniqueness, fairness, uncoercibility, receipt-freeness, individual verifiability and accuracy. Lastly, a method to analyse voting systems based on security requirements is suggested, and a detailed analysis of the proposed protocol, which uses this method, concludes this study.