The process of securing communication and encoding all types of electronic and computer communication is known as cryptography. It is used to secure information from the third parties. The main concepts on which modern cryptography is based are authentication, non-repudiation, data integrity, confidentiality and data integrity. Cryptography uses elements of mathematics especially the computational number theory to encrypt the messages. This book studies, analyses and upholds the pillars of cryptography and its utmost significance in modern times. The topics covered in it deal with the core aspects of the area. This textbook is a complete source of knowledge on the present status of this important field.