Contamination in Cryptographic Protocols

We discuss a foundational issue in multi-prover interactive proofs (MIP) which we call "contamination" by the verifier. We propose a model which accounts for, and controls, verifier contamination, and show that this model does not lose expressive power. A new characterization of zero-knowledge naturally follows. We show the usefulness of this model by constructing a practical MIP for NP where the provers are spatially separated. Finally, we relate our model to the practical problem of e-voting by constructing a functional voter roster based on distributed trust

Blockchain technology in the area of e-Governance – Guidelines for implementation

Dissertation presented as the partial requirement for obtaining a Master's degree in Information Management, specialization in Information Systems and Technologies ManagementThe perception of the public administration among society is widely associated with the area before the digital age and the information revolution: Less efficiency, less democratic, partially transparent, majorly bureaucratic, insufficient service quality, and slow responsiveness. Driven by information and communication technologies, there is an urgent need for disrupting the public sector to improve government decisions, increase the trust of citizens and their participation possibilities as well as enhance government accountability and transparency. The blockchain as a novel and innovative technology with its underlaying technological concept provides a plausible solution to reinvent the public administration processes and transactions with other governments, businesses, or citizens. This dissertation follows a design science research approach to apply multiple analytical methods and perspectives to create an artifact. The type of evidence within this methodology is a systematic literature review, with the goal to attain insights into the current state-of-the-art research of blockchain technology in the area of e-Governance. Additionally, proven best practices from the industry are examined in depth to further strengthen the credibility. Thereby, the systematic literature review shall be used to pinpoint, analyze, and comprehend the obtainable empirical studies and research questions. This methodology supports the main goal of this dissertation, to develop and propose evidence-based practice guidelines for the implementation of blockchain technology that can be followed by the public administration

An Analysis of Chaum's Voter-Verifiable Election Scheme

Chaum's Voter-Verifiable election scheme introduces a new direction for electronic voting. The scheme eliminates the need to trust any machinery or authority, and instead relies on mathematical proof to certify the trustworthiness of an election. Audits at every stage of the election create transparency that should restore voter confidence in the election process. We survey and categorize the field of electronic voting, and place Chaum's scheme within this context. We then define a framework of formal requirements of a voting system. We present Chaum's scheme itself, and give an analysis. Based on our technical analysis, we find the scheme to be secure. However, after considering other implementation concerns, we recognize various minor obstacles limiting its widespread adoption in today's elections. Despite this, we believe that the substance of the scheme is promising and maybe an improved, simpler variant might better suit future elections

Koinonia: verifiable e-voting with long-term privacy

Despite years of research, many existing e-voting systems do not adequately protect voting privacy. In most cases, such systems only achieve "immediate privacy", that is, they only protect voting privacy against today's adversaries, but not against a future adversary, who may possess better attack technologies like new cryptanalysis algorithms and/or quantum computers. Previous attempts at providing long-term voting privacy (dubbed "everlasting privacy" in the literature) often require additional trusts in parties that do not need to be trusted for immediate privacy. In this paper, we present a framework of adversary models regarding e-voting systems, and analyze possible threats to voting privacy under each model. Based on our analysis, we argue that secret-sharing based voting protocols offer a more natural and elegant privacy-preserving solution than their encryption-based counterparts. We thus design and implement Koinonia, a voting system that provides long-term privacy against powerful adversaries and enables anyone to verify that each ballot is well-formed and the tallying is done correctly. Our experiments show that Koinonia protects voting privacy with a reasonable performance

SoK: Secure E-Voting with Everlasting Privacy

Vote privacy is a fundamental right, which needs to be protected not only during an election, or for a limited time afterwards, but for the foreseeable future. Numerous electronic voting (e-voting) protocols have been proposed to address this challenge, striving for everlasting privacy. This property guarantees that even computationally unbounded adversaries cannot break privacy of past elections. The broad interest in secure e-voting with everlasting privacy has spawned a large variety of protocols over the last three decades. These protocols differ in many aspects, in particular the precise security properties they aim for, the threat scenarios they consider, and the privacy-preserving techniques they employ. Unfortunately, these differences are often opaque, making analysis and comparison cumbersome. In order to overcome this non-transparent state of affairs, we systematically analyze all e-voting protocols designed to provide everlasting privacy. First, we illustrate the relations and dependencies between all these different protocols. Next, we analyze in depth which protocols do provide secure and efficient approaches to e-voting with everlasting privacy under realistic assumptions, and which ones do not. Eventually, based on our extensive and detailed treatment, we identify which research problems in this field have already been solved, and which ones are still open. Altogether, our work offers a well-founded reference point for conducting research on secure e-voting with everlasting privacy as well as for future-proofing privacy in real-world electronic elections