The book is a collection of best selected research papers presented at International Conference on Network Security and Blockchain Technology (ICNSBT 2021), organized by Computer Society of India-Kolkata Chapter, India, during December 2-4, 2021. The book discusses recent developments and contemporary research in cryptography, network security, cyber security, and blockchain technology. Authors are eminent academicians, scientists, researchers, and scholars in their respective fields from across the world.