Committee Chair

Skjellum, Anthony

Committee Member

Brooks, R. R. (Richard R.); Yu, Lu; Kandah, Farah


Dept. of Computational Science


College of Engineering and Computer Science


University of Tennessee at Chattanooga

Place of Publication

Chattanooga (Tenn.)


The blockchain technology revolution and concomitant use of blockchains in various applications have resulted in many organizations and individuals developing and customizing their own fit-for-purpose consensus algorithms. Because security and performance are principally achieved through the chosen consensus algorithm, the reliability and security of these algorithms must be both assured and tested. This work provides a methodology to assess such algorithms for their security level and performance is required; liveness for permissioned blockchain systems is evaluated. We focus on permissioned blockchains because they retain the structure and benefits afforded by the blockchain concept while end users maintain control over their processes, procedures, and data. Thus, end users benefit from blockchain technology without compromising data security. We expect that this methodology and taxonomy can be applied to other types of blockchains. The developed methodology is used to provide a liveness analysis of byzantine consensus algorithms for permissioned blockchains. We provide a Digital Ledger Technologies (DLTs) consensus algorithm classification to understand the miner-selection process. We compile the ``security ingredients'' that enable consensus algorithms to achieve liveness, safety, and byzantine fault tolerance (BFT) in blockchain systems. We organize these requirements as a new taxonomy that describes requirements for security. And, Brewer's theorem is utilized to explain tradeoffs between availability and consistency in consensus algorithm design. This analysis uses formal methods and techniques and is applied to two exemplary consensus algorithms: lightweight mining (LWM) and byzantine fault-tolerant Raft (Tangaroa). Our analysis reveals the liveness of the given consensus algorithm and its ability to protect against malicious miner denial of services (DoS) attacks. Digital signatures are employed to prove integrity and non-repudiation of messages passing in the systems. Queueing theory and Markov chains are applied to determine the average waiting time of client transactions when malicious miners work to slow the system. Queuing theory and Markov chains jointly are employed to test a given blockchain's ability to perform correctly despite the presence of malicious miners or resistant nodes. Overall, the methodology presented here provides a roadmap to guide developers during the design phase of consensus algorithms to render these algorithms more secure and robust.


First of all, I thank God for all the blessings given to me in this life. Thank you to my parents as well as my brothers and my sisters for giving me the encouragement and energy to finish this long journey. I want to express my sincere appreciation to my advisor, Dr. Anthony Skjellum, for all his support throughout my PhD journey. Dr. Skjellum, thank you for your generosity in guiding me and mentoring me with patience and kindness, your insightful support made my PhD experience rich, fulfilling, and great. Your support made it possible for me to complete my dissertation, I could not have done it without you. I am fortunate to have had the opportunity to learn from you and I look forward to continue collaborating with you. I would like to thank Dr. Farah Kandah and Dr. Lu Yu for serving on my committee. I appreciate the time you took to read my dissertation. Your comments and suggestions improved the quality of this dissertation. Special thanks to Dr. Richard Brooks for his invaluable support, input, comments, and guidance. It has been an honor working with all of you and I look forward to continue collaborating with you. To all SimCenter friends and staff, especially Kim Sapp, for the care and love she provided to me since day one. And, finally, to my family and friends, thank you for the prayers and for loving me through it all.


Ph. D.; A dissertation submitted to the faculty of the University of Tennessee at Chattanooga in partial fulfillment of the requirements of the degree of Doctor of Philosophy.




Blockchains (Databases); Formal methods (Computer science)


Blockchain; Byzantine Fault Tolerant Raft; Consensus Algorithms; DLTs Consensus Algorithm Classification; Formal Methods; Lightweight Mining

Document Type

Doctoral dissertations




xvi, 112 leaves