Cryptography/Scytale

The Scytale cipher is a type of transposition cipher used since the 7th century BCE. The first recorded use of the scytale cipher was by the Spartans and the ancient Greeks who used it to transport battle information between generals.

Encryption Using the Scytale

The scytale encryption system relies on rods of wood with equal radiuses. The system is a symmetric key system where the radius of the rod is the key.

After establishing keys a messenger winds a strip of leather around the rod. Then he writes the message going across the rod, so that when he unwinds the leather the letters have been jumbled in a meaningless fashion.

Example: Suppose the rod allows you to write 4 letters around it in one circle and 5 letters down the side. Clear text: "Help me I am under attack" To encrypt one simply writes across the leather...

_____________________________________________________________
    |  |   |   |   |   |   |
    |  | H | E | L | P | M |  
    |__| E | I | A | M | U |__ 
       | N | D | E | R | A |  |
       | T | T | A | C | K |  |
       |   |   |   |   |   |  |
______________________________________________________________

so the cipher text becomes, "HENTEIDTLAEAPMRCMUAK" after unwinding.

Decryption Using the Scytale

To decrypt all you must do is wrap the leather strip around the rod and read across. Example: ciphertext: "HENTEIDTLAEAPMRCMUAK" Every fourth letter will appear on the same line so the cipher text becomes

HELPM...return to the beginning once you reach the end and skip used letters. ...EIAMUNDERATTACK. 

Insert spaces and the plain text returns, "Help me I am under attack"