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> ENIGMA MACHINE




    enigma
    difficulty: 3–7
    based on: Enigma I, Wehrmacht




The idea in plain English: Imagine a combination lock with three rotating discs.
When you press a letter on a keyboard, an electrical signal travels through the discs, bounces
off a reflector at the end, comes back through a different path, and lights up a different letter.
After each key press, the first disc rotates one position — so pressing the same letter twice
produces different outputs. This ever-changing path made Enigma extremely hard
to crack. The starting positions of the three discs (the "key") were changed daily.



Why this really exists: The Enigma machine was used by Nazi Germany in WWII.
The Allied codebreakers at Bletchley Park, led by Alan Turing, developed the Bombe — an
electromechanical computer — to crack Enigma messages. This effort shortened the war by an
estimated 2-4 years and saved millions of lives. It's also considered the birth of modern
computing. Today, the same rotor principle is used in some high-security
mechanical locks.





  
▸ Concrete Example

  
Let's trace one letter through the machine. Rotor I starting at position A, we press "H":

  

    1. Signal enters at H (position 7)

    2. Rotor I wiring maps 7→4 (E) — the rotor's internal wiring scrambles the letter

    3. Rotor II maps 4→10 (K)

    4. Rotor III maps 10→21 (V)

    5. Reflector B maps V→? (reflector sends it back through a different path)

    6. Signal returns through rotors in reverse order

    7. Output: some other letter (let's say "Q")


    H → Q (this time). Press H again → different output (because rotor rotated!)
  

  
The magic property: encrypting and decrypting are the same operation.
  Type "Q" into a machine with the same settings and you get "H" back. That's the reflector's doing.







  
▸ How to Solve (Step by Step)

  

    
1. Set rotors to the given starting positions

    
2. For each ciphertext character:
      
— Advance the rightmost rotor by 1 position (if it wraps, advance the next rotor)
      
— Pass the signal through each rotor's wiring (accounting for current rotor offset)
      
— Pass through the reflector
      
— Pass back through rotors in reverse order
      
— Record the output character

    
3. The resulting string is the decoded message (which is also the answer)

  

  

    # The rotors and reflector are simple substitution tables:

    rotor_I =  "EKMFLGDQVZNTOWYHXUSPAIBRCJ"  # A→E, B→K, etc.

    rotor_II = "AJDKSIRUXBLHWTMCQGZNPYFVOE"

    rotor_III = "BDFHJLCPRTXVZNYEIWGAKMUSQO"

    reflector_B = "YRUHQSLDPXNGOKMIEBFZCWVJAT"


    # Important: the rotor offset changes the wiring:

    # If rotor is at position 3, then input letter A (0)

    # actually maps through position (0+3)=3 → D in the rotor table
  

  
💡 The standard Enigma I used 3 out of 5 possible rotors, chosen daily. The puzzle tells you which 3 rotors are used and their starting positions.






  
▸ Real-World Applications

  
    
    
  • Modern computing: The Bombe (Enigma-cracking machine) was a direct ancestor of modern computers
    • 
    
  • Smart cards: Some high-security chip cards use rotor-like scrambling internally
    • 
    
  • History: What Alan Turing and Bletchley Park achieved changed the course of WWII and computing
    • 
    
  • Cryptography education: Enigma is the perfect case study in "why good encryption needs keys to be random and frequently changed"
    • 
  






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