Leon Battista Alberti
, commonly thought of as the Father of Western Crypology
, designed a disk to allow a more complex form of polyalphabetic substitution
. The disk acts as a quick cipher
It is constructed out of two copper plates, one large, and another smaller disk inside the large one. The small ring is able to roate inside the larger one, and has written each letter of the alphabet along its circumference. On the outer ring there are 20 letters (missing H, J, K, U, W, and Y), but has added the numerals 1 through 4. The outer disk is used to generate the plaintext, using the ciphertext selected on the inner ring.
For the system to work, each correspondent needs to have a matching disk. When the system was used, usually the letters on the wheels were even re-arranged mid-message, signaled by reaching a point of mutual agreement. Because each position shift initiated a brand new cipher alphabet, this was actually the very first polyalphabetic cipher.
Alberti's disk, in part, led to the development of enciphered code, which in part is the bases for many modern applications of cryptography.Porta's Disk which used symbology and polyalphabetic substitution, was based upon this model.