Nowadays the Internet provides communications between millions of people, all basically strangers, and every day it?s used as a tool for the increasingly popular ecommerce. With all this data exchange which includes private communications, commercial transactions, etc., security becomes a major player in protecting personal information. A key aspect for secure communications is played by Cryptography.

Cryptography is the science of securing data while Cryptanalysis is the science of analyzing and breaking secure communication. They are both part of Cryptology. This paper presents an overview of Cryptography.

Cryptography is the study of mathematical techniques related to aspects of information security such as confidentiality, data integrity, entity authentication, and data origin authentication. It enables you to store sensitive information or transmit it across insecure networks (like the Internet) so that only the intended recipient can read it.

A cryptographic algorithm (or cipher) is a mathematical function used in the encryption and decryption process.

It works in combination with a key (a word, number, or phrase) to encrypt the plaintext. The same plaintext encrypts to different ciphertext with different keys. The security of encrypted data is entirely dependent on two things: the strength of the cryptographic algorithm and the secrecy of the key. A cryptosystem is comprised of a cryptographic algorithm, plus all possible keys and all the protocols that make it work.