The study of the techniques that are utilized to ensure secure communication in the presence of adversaries is known as cryptography. It includes the analysis and construction of the protocols to prevent the public or third parties from reading private messages. The aspects that are central to modern cryptography are related to confidentiality of data, authentication, data integrity, and non-repudiation. Modern cryptography is classified into various areas of study such as symmetric-key cryptography, cryptanalysis, cryptosystems, public-key cryptography and cryptographic primitives. Various disciplines that contribute to cryptography are computer science, communication science, mathematics, physics and electrical engineering. Cryptography is applied in fields such as electronic commerce, computer passwords, military communications, chip-payment cards and digital currencies. This book attempts to understand the multiple branches that fall under the discipline of cryptography and how such concepts have practical applications. Most of the topics introduced herein cover new techniques and the applications of this field. This book is a complete source of knowledge on the present status of this important field.