In 404 BC when the Persians conspired to attack the Spartans, a messenger to Lysander of Sparta carried a secret message written upon his belt. Lysander wound this belt around a tapered wooden staff and read the message that enabled him to prepare for, and ultimately defeat, the Persian invaders.

The Spartans used a very simple method to hide the message. The tapered staff is called a scytale. To use it the Spartans would wind a strip of parchment around it and write the message upon the strip along the length of the scytale; once the strip was unwound, it could not be read again until it was wound around a scytale of the same size as the original.

Broadly put, cryptography is the science of keeping communications private so only the people for whom they are intended can read them; cryptanalysis is the science of breaching the protection...