Leon Battista Alberti (1404 - 1472) Invented what was probably the first polyalphabetic cipher in 1466.
It consisted of a fixed outer disc containing the plain text and a moveable inner disc with the corresponding cipher text. To encipher a message you have to decide on the starting position of the inner disc, this forms part of the key.
The other part of the key is to decide on a rule for the movement of the
inner disc for example it could be moved 5 positions anti-clockwise every 8th letter.
The program below can be downloaded to print out cipher discs. Alberti's disc had 24 positions with 20 letters and 4 numbers in the outer disc. The numbers could represent anything decided between the users.
Hence his system also allowed the use of codes. The program will generate Alberti's original disc and also a 26 position A-Z disc.
The inner and outer discs will be printed side by side, what you have to do is glue the discs onto an empty cornflake packet, or similar, cut them out and fasten together with a 'butterfly' paper clip.
You may also recognise this cipher as the Captain Midnight Decoder Badge.
This program generates Alberti's Cipher Discs, that you can print, cut out and assemble.
