Giambattista della Porta
Neapolitan natural philosopher whose 1563 treatise described a polyalphabetic cipher where the key letter selects one of thirteen alphabet pairs.
Della Porta (1535–1615) was a Neapolitan polymath, and his De furtivis literarum notis (1563) is one of the earliest printed treatises on cryptography with a systematic account of polyalphabetic ciphers. His system splits the alphabet into halves, A–M and N–Z, and the key letter decides which pair of reciprocal substitutions applies. The scheme is simple, and it is less famous than Vigenère's, but it is one of the earliest polyalphabetic systems in print.