Leon Battista Alberti
Renaissance architect who described a cipher disk with movable alphabets around 1467.
Leon Battista Alberti (1404–1472) was an architect, writer and one of the most versatile minds of the Italian Renaissance, today best remembered for the treatise De re aedificatoria. Around 1467 he wrote De cifris, which describes a cipher disk with two concentric rings. The outer ring is fixed and the inner one can be turned, so the relationship between plaintext and ciphertext changes as the message goes on.
It is one of the earliest known descriptions of polyalphabetic encryption in Western Europe. The idea that the same letter should be encrypted differently depending on its position lies behind both the Vigenère cipher and, centuries later, the rotors of the Enigma. Alberti's disk was the starting point for a long line of methods and machines.