Tis an Enigma

Jed Rembold

April 6, 2026

Starting the Final Stretch!

Scan the QR code or go to https://tools.jedrembold.prof/daily
Fun group question: Have you encrypted things before? What sort of cipher did you use?

I’m going to try for Midterm 2 feedback to you by Friday, but more realistically it will probably be a week from today
I will see about getting grade reports sent out tomorrow though that include PSets 4 & 5 and Breakout
Enigma guide goes out later tonight
- You essentially have two weeks for this one. Use the time wisely!

How are the parts of an Enigma machine connected?
How do the rotors work, and how does changing a rotor change the wiring connections?
How can we encrypt and decrypt messages with an Enigma Machine?

To get us going, we are going to construct simple paper versions of the Enigma Machine!
- All groups should have 1-2 templates
Cut out the 4 “parts”, and carefully tape them as indicated to create a tube and three rings
The rings should be able to fit around the tube, but should fit snuggly

Slide the rotors onto the tube so that they are in ascending numerical order from left to right
Position all rotors so that the left “A” line aligns with the tube “A” line
- We’ll call this the AAA rotor position
Now, DO NOT SHIFT THE ROTORS
One cool attribute about the Enigma machine is that it is symmetric: you use it the same way for both encryption and decryption.
Decrypt my secret message to you: EBUMJUF

In practice though, the fast rotor moves up one position before each signal is passed through
Decided on a starting rotor configuration, making them all different
- So each rotor should start with a different left letter on the bold “A” line
- Write it down!
Now, decide on a one-word message you want to encrypt. Make it at least 5 letters!
Work out and write down what the encrypted message would be
Keep in mind that:
- Rotors advance up the alphabet (so turn away from you) before you trace the signal through
- If one rotor moves from Z back to A, you also need to advance the rotor to the left of that rotor by one

I’m going to collect and redistribute all the secret messages
Given the starting rotor positions and the message, can you decrypt the message?

Project 4 has slightly more milestones than past projects, but each is still meant to give you a testable aspect of the program that you can bite off one piece at a time
- Milestone 0: Activate the keyboard when pressed
- Milestone 1: Connect the keys directly to the lamps (no encryption)
- Milestone 2: Design and implement rotors
- Milestone 3: Implement one stage in the encryption (through 1 rotor)
- Milestone 4: Implement the full encryption path
- Milestone 5: Make the rotors advance properly each key press
Web examples exist for helping you test each step of the process, linked here and in the guide.

The Enigma project is designed using the common model, controller, view paradigm
Breaks an interactive program up into 3 pieces:
- The controller: the piece that deals with user input
- The view: the piece that handles graphical output
- The model: the piece that controls what should be happening at any given time

In the Enigma project, the view and the controller are handled for you
- Both are actually handled in the same module
- Both export various methods that you can use to get input or interact with them from within the model
You are responsible for writing the code that comprises the model
There is also a constants module, where all of the various constants that you may need are stored