Techniques to protect secrets have been around for centuries. The earliest attempts to secure and hide data from adversaries date back to ancient inscriptions discovered on monuments in Egypt, where a special alphabet that was known by only a few trusted people was used. This early form of security is called obscurity and is still used in different forms today. In order for this method to work, it is critical to protect the secret, which is the meaning of the alphabet. Later in time, finding foolproof ways of protecting important messages was important in both World War One and World War Two. In the late-20^th century, with the introduction of electronics and computers, sophisticated algorithms were developed to secure data, giving rise to a whole new field called cryptography. This chapter discusses the algorithmic aspects of cryptography. The purpose of these algorithms is to allow secure data exchange between two processes or users. Cryptographic algorithms find strategies of using mathematical functions to ensure the stated security goals.