Paper Enigma Machine

"I've had many fine emails from people who have enjoyed the Paper Enigma. Many have been confused about the subtlety of the motion of the rotors. One of the benefits of building and using a model like this is that you can gain a deeper understanding of the details of the Enigma machine.

Note that the VERY FIRST STEP before encoding (or decoding) each character is to move the rotors. That is why, even though the starting position of my sample is "MCK" - the rotors are moved to the "MCL" position while decoding the first letter. Also note that any rotor motions should be done in one step (the actual Enigma machine uses a pawl to rotate 1, 2, or all 3 rotors all at once when a letter key is pressed - and before a lamp is lit with the encoded letter). The right rotor always moves up by one space; the other rotors move up if the rotor to their right has the up-arrow symbol in the first row. If you move the rotors from right-to-left, you'll end up making a mistake by rotating a center or left hand rotor one character too early."

Paper Enigma Machine
by Mike Koss