The book focuses on a paradigm of blockchain technology that addresses cyber security.The challenges related to cyber security and the solutions based on Software Defined Networks are discussed.The book presents solutions to deal with cyber security attacks by considering real-time applications based on IoT, Wireless Sensor Networks, Cyber-Physical Systems, and Smart Grids.The book is useful for academicians and research scholars worldwide working in cyber security.It is also useful for industry experts working in cyber security.