EXAMPLE 20 Jefferson Wheel Cipher

To illustrate the Jefferson cipher, we use a system with only six disks labeled as follows:

  • 1: XWAZJGDLUBVIQHKYPNTCROSFEM
  • 2: EBPLNKACZDTRXMJQOYHGSVUFIW
  • 3: EQGYXPLOCKBDMAIZVRNSJUWFHT
  • 4: UKTEBSXRPLNDVHGFCQYIZMJWAO
  • 5: GJVDKCPMNZQWXYABEUOTSIHFRL
  • 6: KGAMIHWPNYCJBFZDRUXLQOTVES

To send the message ATTACK, we select a key such as 4, 2, 5, 1, 6, 3 and arrange the disks in that order. We then rotate the six disks so that the word ATTACK appears as a row as shown below (only the first eight rows are provided).

4 2 5 1 6 3
A T T A C K
O R S Z J B
U X I J B D
K M H G F M
T J F D Z A
E Q R L D I
B O L U R Z
S Y G B U V

If we select as our substitution row the one immediately below the row with the word ATTACK, the encrypted message is ORSZJB. Had we selected as our substitution row the one that is three below our message, we would have obtained the encrypted message KMHGFM. Each of the 25 rows is equally effective for encryption purposes.

Conversely, had we received the ciphertext KMHGFM, we would have rotated disk 2 so that M appeared in the same row as K on disk 4, then rotated disk 5 so that H appeared in the same row as KM, then continued in the same way until the row became KMHGFM. Then we would have looked for another row that is a sensible word, such as ATTACK.