Cryptography is the science that studies various mathematical aspects of information security used to protect data that is communicated over an insecure channel or stored in an unprotected medium. As Rivest said, it "is about communication in the presence of an adversary" [1]. Though historical records indicate the usage of secret messages around 4000 years ago, cryptography, as we see it today, is just less than 100 years old. The military and governments predominantly used classical cryptography to maintain the confidentiality of the information communicated. With the advent of computers and the internet, cryptography became more and more ubiquitous by being part of a multitude of applications, and now each of us knowingly or unknowingly employs it while using internet banking, e-commerce, smartphones, Internet of Things (IoT), etc. Apart from confidentiality, which is considered the central aspect of information se- curity, modern cryptography focuses on three fundamental services: integrity, authen- tication, and non-repudiation. The set of algorithms used to provide these information security functions is known as cryptosystem. A present-day cryptosystem addresses the following: