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The Realization of a Blockchain-Based E-Voting Solution With a New Consensus Algorithm
(01. Izmir Institute of Technology, 2022) Karaçay, Mustafa; Şahin, Serap; Şahin, Serap; 03.04. Department of Computer Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
Security and transparency issues in the paper-based voting system and technological advances popularized e-voting systems. Many academic research and industrial solutions have recently been proposed, designed, and implemented with a Homomorphic Cryptography Scheme or HTTPS. However, there is a new popular player in the game which is called blockchain technology. This study analyzes the requirements of a welldesigned e-voting system and the technology behind the blockchain, and proposes an e-voting system with a novel consensus algorithm. Different strategies are designed and implemented to satisfy all requirements. First, RSA and Paillier Homomorphic Cryptosystem are applied to meet requirements such as individual verifiability, secrecy, etc. So that no one can modify the vote; however, any voter can verify his/her vote during the whole vote period. Second, different blockchains are used to meet requirements such as eligibility, privacy, authentication, etc. So that the system detects whether the data is coming from an eligible or a non-eligible voter. The system ensures that votes and voters can not be correlated if it is an eligible voter. So, the privacy of eligible voters is always protected. Third, our blockchains ensure Consensus throughout the voting process. Fully replicated, distributed, transparent, and secure blockchains ensure that everything is under control. Fourth, internal control mechanisms are applied to meet requirements such as nonreusability, coercion-resistance, etc. So that eligible voters can cast just one vote within the specified period. The system keeps every sensitive data encrypted so that no one manipulates the results before the vote ends.
P/Key: Puf Based Second Factor Authentication
(01. Izmir Institute of Technology, 2022) Akgün, Mete; Şahin, Serap; Uysal, Ertan; Akgün, Mete; Şahin, Serap; 03.04. Department of Computer Engineering; 01. Izmir Institute of Technology; 03. Faculty of Engineering
Second-factor authentication mechanisms increase the security of authentication processes by implementing an additional auxiliary layer to a single factor. As a second factor, using one-time passwords (OTP) is mainly preferred due to their hardware independence and easy generation. OTP generation protocols should be evaluated in two main categories: time and security. In time-based OTP mechanisms (TOTP), client and server store a shared secret key. However, if attackers compromise the server, attackers can generate new OTPs using the key and impersonate the client. To solve this problem, protocols based on the hash chain mechanism have been proposed; however, these methods have weaknesses mainly due to the authentication speed and the limited number of OTPs they generate. This thesis proposes a server-side tamper-proof and fast response physical unclonable function (PUF) based second-factor authentication protocol on overcoming these problems. PUF is a digital fingerprint that ensures that every device produced is unique due to uncontrollable factors in the production stages of devices. It generates responses that correspond to challenges. Since PUF is based on the micro-level differences in devices, micro-level structure changes in the event of an attack, and the PUF takes to generate different responses. Although PUF is a fast response function, it is impossible to reach the challenge from the response it generates. In the proposed protocol, the PUF inside the server generates key values and used to store clients’ secret seed values securely. In case of side-channel attack on server-side, the key values of the clients cannot be obtained by the attackers, as the PUF structure will be corrupted. Even if the attacker obtains the server’s credentials and gains access to the system, they cannot get the secret seed values of the clients and cannot generate the OTPs. In this way, the attacker cannot authenticate by impersonating the client.
A Study on Early Decryption Mechanism at Veriflable Delay Functions
(01. Izmir Institute of Technology, 2022) Özdemir, Oğulcan; Şahin, Serap; Şahin, Serap; 03.04. Department of Computer Engineering; 01. Izmir Institute of Technology; 03. Faculty of Engineering
In computer science, can we measure the passage of time in accordance with Earth time and use this measurement mechanism as a time lock to decrypt encrypted data? The search for answers to these questions has not yet been given a definite, straightforward answer. Because there is no fixed definition of time in computer science. Research on the use and measurement of "time-locked cryptography" in computer science is based on the research of Time-Lock Puzzles and Timed-Release Crypto by Rivest et al. In 2017, two studies were published that accelerated development in this area: Simple Verifiable Delay Functions and Efficient Verifiable Delay Functions. In both studies, timing requirements are defined as Verifiable Delay Functions (VDF). However, current VDF solutions do not have a controlled early decryption feature for time locking mechanism. The contributions we intend to make to the VDF protocol in this study focus on the design, verification, and implementation of a new VDF protocol that both guarantees the time lock mechanism requirements defined by VDF and provides the ability to open the time lock in a controlled manner by authorised individuals before the target time. VDF solution to be developed, unlike similar VDF protocols, should also include the blockchain Ethereum component and work flexibly with any of the defined VDF time lock algorithms, depending on which one is chosen.

Master Degree / Yüksek Lisans Tezleri

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