The Confederate cipher disc was a device used by the Confederate Army during the American Civil war, from 1862 to 1865.
It is composed of 2 concentric discs, each with a regular alphabet, around an axle. There is a third disc on the back, to allow the outer disc’s rotation while holding the device in hand.
Use
To encipher
The outer disc is rotated so the first letter of the key on its alphabet aligns with “A” on the inner disc’s alphabet.
The first plain letter is located on the inner disc, and the cipher letter is read opposite it on the outer disc.
The operation is then performed again with the next plain letter and next key letter, and so on.
The key is repeated after the last letter is reached.
To decipher
The decryption process is the same.
The outer disc is rotated so the first letter of the key on its alphabet aligns with “A” on the inner disc’s alphabet.
The first cipher letter is located on the outer disc, and the decrypted letter is read opposite it on the inner disc.
The operation is then performed again with the next cipher letter and next key letter, and so on.
The key is repeated after the last letter is reached.