Cryptography (or cryptology; erived from Greek κρύπτω krýpto "hidden" and the verb γράφω gráfo "to write" or λέγειν legein "to speak") is the practice and study of hiding information. In modern times, cryptography is considered to be a branch of both mathematics and computer science, and is affiliated closely with information theory, computer security, and engineering. Cryptography is used in applications present in technologically advanced societies; examples include the security of ATM cards, computer passwords, and electronic commerce, which all depend on cryptography.