Florence and a Leap in Cryptography: The Leon Battista Alberti Cypher Disk

Cryptography is an art born with politics and war from the necessity of communicating at a distance preventing eavesdroppers from understanding the message. The earliest examples are the Greek, Roman and Arab cyphers, based on various kind of pre-defined letter substitutions. The first true leap forward in cryptography in the first two millennia of its recorded history was due to Leon Battista Alberti, who, in 1466, conceived the idea of a cypher where letter substitution scheme varied within the same message thanks to a device: the cypher disk. This concept of polyalphabetic substitution was later applied in many famous cryptography techniques and eventually developed in the Enigma machine used by Germany in World War II. Enigma provided such a robust code that, from its deciphering effort, the brand-new science of electronic computing and relative technology eventually evolved.