Al-Kindi discusses decryption of messages: 8th century

The Lorenz cipher machine as used in WWII

Symmetric-key cryptography, where a single key is used for encryption and decryption

Cryptography, or cryptology, is the practice and study of hiding information. It is sometimes called code, but this is not really a correct name. It is the science used to try to keep information secret and safe.

Modern cryptography is a mix of mathematics, computer science, and electrical engineering. Cryptography is used in ATM (bank) cards, computer passwords, and shopping on the internet.