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.