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An Enigma simulator.

Named after the designation given by 🇬🇧 British military intelligence to wartime signals intelligence obtained by breaking encrypted enemy communications. Click here for more information.

The project can simulate Enigma I, Enigma M3 and Enigma M4 machines used by the German Armed Forces (Wehrmacht) during the Second World War.

Most information regarding the operation/design of Enigma machines was sourced from https://www.cryptomuseum.com/crypto/enigma/i/index.htm and https://www.cryptomuseum.com/crypto/enigma/working.htm.

The primary components of the machine are:

• Rotors
  • Each rotor has 26 electrical contacts on each face, representing the letters of the alphabet. It contains 26 wires, directly linking each letter to another letter, for example an H could be transformed into a Y.
  • Each rotor also has 26 possible starting positions, again representing the letters of the alphabet.
  • To add more complexity, each rotor has a 'ring setting' which offsets the alphabetical values from their electrical wiring.
  • On every key press, the rightmost rotor rotates. When a rotor completes a full rotation (26 key presses), the rotor to the left will rotate once.
  • A strange concept called double stepping occurs where the middle rotor will rotate when the rightmost rotor has completed a full revolution, or if it has completed a full revolution itself, it will rotate once more.
  • Enigma I and Enigma M3 have three rotor slots, although the Enigma M4, later used by the Kriegsmarine (German Navy), contains four.
  • Enigma I operators usually had a choice of five rotors, numbered I, II, III, IV and V.
  • Enigma M3 operators had three extra rotors to choose from, numbered VI, VII and VIII.
  • Enigma M4 operators also had an extra two rotors which fitted into a fourth rotor slot between the reflector and left rotor. The fourth rotors differ from other rotors in that they do not rotate and do not have any notches. They are labelled β (Beta) and γ (Gamma).
• Reflector
  • Contains thirteen wires which pair letters together. For example, if B was electrically wired to U, a B entering the reflector would leave as a U and vice versa.
  • The way the reflector was designed means, however, that no letter can ever be encrypted to itself - this was a severe flaw with Enigma that was exploited by codebreakers.
  • There are three different reflector configurations, labelled A, B and C.
• Plugboard
  • Allows the operator to easily pair letters together in a similar way to the reflector.
  • For example, if an operator plugged one end of a wire into B and the other end into K, a B entering the plugboard would leave as a K and vice versa.
  • Usually up to 10 pairs would be configured. If a letter does not have a counterpart, it leaves the plugboard as itself.

Operation of the machine:

1. The operator presses a key.
2. The signal first goes to the plugboard, which would transform the letter into another letter, if it had a corresponding letter.
3. The rotors would rotate before any signal passes through them.
   • Rotor stepping is explained above, including double stepping.
   • Enigma M4 'fourth rotors' do not rotate.
4. The signal then passes through the rotors from right to left, being transformed at each step, until it reaches the reflector, at which point it is transformed into its paired letter. It then goes back through the rotors in reverse order, i.e. left to right.
5. It then reaches the plugboard again, where the signal is transformed into its paired letter yet again (if it has a paired letter).
6. Finally, the signal goes to the lamps in the centre of the machine. The lamp for the letter corresponding to the signal will light up.

Implementation details

Within the code, characters are represented as int-typed values. This makes calculating offsets much easier. They are translated from rune to int at the start of an operation, then back to int at the end to be displayed to the user.