Cryptography for Innovative Blockchain Services

Abstract

Since the advent of Bitcoin, scientific interest in its underlying core technology Blockchain has been thriving. Much work has been carried out for blockchain use cases in different industrial areas such as healthcare, Internet of Things (IoT), supply chain, and decentralized finances, to name a few. The research addressed some generic and well-defined topics adapted as challenges for the blockchain, such as its security, privacy, scalability, and fairness. To solve these challenges, a plethora of research employed cryptography as its founding basis. The thesis aims to address the challenges mentioned above. The starting point of the thesis is to investigate and scrutinize cryptographic primitives, schemes, and protocols that are or can be used to solve some of the issues identified in blockchain and improve the current state-of-the-art designs. The thesis consists of four main topics. The first topic addresses how to construct an energy-efficient, fair consensus mechanism. For that, two novel consensus mechanisms are presented in the thesis. The second topic covers the use of client puzzles for Denial of Service (DoS) attack mitigation. The thesis includes two works about DoS attacks; the first work presents a new construction of a client puzzle scheme; the second work studies the DoS attack in the blockchain ecosystem and proposes a few mitigation techniques, including a client puzzle scheme. The third topic in the thesis assesses the privacy of cryptocurrency systems. Two papers contribute to this topic: the first paper offers a novel construction of a privacy-preserving cryptocurrency system and models the system’s security; the second paper employs the work developed in the first paper to construct a general security model for the existing privacy-preserving cryptocurrency systems. The fourth topic is about decentralized randomness beacon protocols. These protocols are essential to generate publicly verifiable, trusted randomness used in consensus mechanisms and smart contracts. Two papers contribute to this topic: the first paper presents a systematization of knowledge of existing decentralized randomness beacon protocols; the second paper proposes a new protocol for randomness generation using blockchain as a bulletin board.