A Cipher Disk is a cryptological device that can be used for enciphering and deciphering messages. The development of the cipher disk is attributed to Leon Battista Alberti in the 15th Century. Its development is considered a milestone in cryptology.
The cipher disk has two scales, one with an ordered alphabet, or plaintext scale, the other with a scrambled or cipher alphabet. The cipher disk can be used for either simple (monalphabetic) substitution ciphers, where the same cipher character represents the same original character (or plaintext character) throughout a message, or for polyalphabetic ciphers, where a cipher may represent different plaintext characters, using some agreed-upon scheme between the sender and the receiver.
The polyalphabetic aspect of Alberti's device was considered so significant that the cipher disk itself is often overlooked in discussions of cryptological methods. Yet the cipher disk could be used as a compact device to replace a Vigenère cipher tableau, and indeed was used in this fashion by Confederate forces during the American Civil War.
In its simpler applications, the cipher disk was used as a business communication tool and for novelties, such as radio premiums.
Further reading
- The Code Breakers, by David Kahn (New York, Scribener 1996, ISBN 0-684-83130-9)
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