Cipher disk

A cipher disk is an enciphering and deciphering tool developed in 1470 by the Italian architect and author Leon Battista Alberti.

He constructed a device, (eponymously called the Alberti cipher disk) consisting of two concentric circular plates mounted one on top of the other.

Rather than using an impractical and complicated table indicating the encryption method, one could use the much simpler cipher disk.

To make the encryption especially hard to crack, the advanced cipher disk would only use combinations of two numbers.

[2] Cipher disks would also add additional symbols for commonly used combinations of letters like "ing", "tion", and "ed".

A metal cipher disk
Reconstruction of an Aeneas cipher disk, 5th century BC, Thessaloniki Science Center and Technology Museum
Modern representation of the Union Cipher Disk, from the American Civil War , which was 3.75 inches (95 mm) in diameter and made of light yellow heavy card stock. It consisted of two concentric disks of unequal size revolving on a central pivot. The disks were divided along their outer edges into 30 equal compartments. The smaller inner disk contained letters, terminations and word pauses, while the outer disk contained groups of signal numbers. For easier recognition, the number eight represented two. The initials A.J.M. represent the Chief Signal Officer General Albert J. Myer . Each disk had a control number used for accountability.