cipher disk
Quick Summary
Used in the field by the U.S. Army Signal Corps at the beginning of World War I, the disk enabled messages to be quickly encrypted with a simple substitution cipher by rotating the inner ring.
A cipher disk is a device used in cryptology for enciphering and deciphering messages. It consists of two concentric, movable disks with the alphabet written around their edges. By rotating the disks, different substitution ciphers can be created, where each letter in the plaintext is replaced by a different letter in the ciphertext. This method is a form of substitution cipher, a basic type of encryption where plaintext units are replaced by other symbols.12
Cipher disks were among the earliest mechanical devices used for secret communication, with early versions appearing around the late 1400s for diplomatic purposes. While simple, these devices were a step towards more complex encryption machines that would be developed later, particularly during World War II.34
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