The main objective of this book is to cater to the need of a quality textbook for education in the field of information security. The present third edition of the book covers the principles, design, and implementation of various algorithms in cryptography and information security domain. The book is a comprehensive work with a perfect balance and systematic presentation of the theoretical and practical aspects. The pre-requisite of the cryptography are the fundamentals of the mathematical background. The book covers all such relevant methods and theorems, which are helpful to the readers to get the necessary mathematical base for the understanding of the cryptographic algorithms. It provides a clear analysis of different algorithms and techniques. new to the third edition New chapters on o Cyber laws o vulnerabilities in TCP/IP model revised sections on o digital signature o attacks against digital signature introduction to some open source tools like Nmap, zenmap, port Scanner, network Scanner and Wireshark revised section on block cipher modes of operation coverage of simplified data encryption standard (s-des) and simplified advanced encryption standard (s-aes) with examples elaborated section on linear cryptanalysis and differential cryptanalysis New solved problems and a topic “primitive roots” in number theory br>Chapter on public key cryptosystems with various attacks against RSA algorithm New topics on ransomware, dark NET, and dark web as per the current academic requirement revised br>Chapter on digital forensics The book is intended for the undergraduate and postgraduate students of computer Science and engineering (B.Tech/M.Tech), undergraduate and postgraduate students of computer Science (B.Sc./ M.Sc. Computer Science), and Information Technology (B.Sc./ M.Sc. It) and the students of Master of computer Applications (MCA).