This book presents some critical security challenges that are faced in today's computing world. It discusses, in detail, the defense mechanisms against these kinds of attacks with the help of classical and modern approaches of cryptography and other defense mechanisms. The book not only deals with theoretical and fundamental aspects of cryptography, but also talks in length about different applications of cryptographic protocols and techniques in designing computing and network security solutions. This book will prove itself to be beneficial for researchers, engineers, graduate and doctoral students who are working in the same and related field.