Classical Period (800 BCE - 500 CE)

The classical period marked the first systematic approaches to cryptography, featuring developments primarily in Greece and Rome.

Greek Contributions

The Greeks introduced several important cryptographic systems:

• The Scytale, used by Spartan military commanders, was one of the first transposition ciphers
• Herodotus documented the practice of steganography through tattooing secret messages on slaves' heads
• Polybius created the Polybius square, a device that converted letters into pairs of numbers

Roman Innovations

Julius Caesar developed the famous Caesar cipher, shifting letters of the alphabet by a fixed number of positions. This represented one of the first documented uses of substitution ciphers and remained influential for centuries.

Other Classical Cryptographic Techniques

Atbash Cipher

The Atbash cipher is a simple substitution cipher originally used for the Hebrew alphabet. It replaces each letter with its reverse (e.g., A becomes Z, B becomes Y).

The Alberti Cipher Disk

Though not from the classical period, the Alberti cipher disk, invented by Leon Battista Alberti in the 15th century, was inspired by earlier classical techniques. It allowed for polyalphabetic substitution, which was a significant advancement over the simpler ciphers of the classical era.

Steganography in Ancient China

In ancient China, steganography was practiced by writing messages on fine silk, which was then rolled into a ball and covered in wax. The wax ball could be swallowed by a messenger to avoid detection.

These early cryptographic methods laid the groundwork for more complex systems developed in the medieval and modern periods.