The Enigma Machine

Workflow

• Basic configuration: Reflector - Rotor 3 - Rotor 2 - Rotor 1 - Plugboard, the character that need to be enciphered flows from right to left.
• Two main process:
  1. Foward: character flows from the rightmost rotor to the leftmost one.
  2. Backward: character flows from the leftmost rotor to the rightmost one.
• When a character enters the machine, The Plugboard swap() the character to another one based on its setting.
• The character then enters the machine and the forwarding process starts (from right to left).
• There are 3 rules for each time a character enters the machine:
  1. The rightmost rotor always takes a single step before enciphering the character.
  2. If any rotor (except the leftmost) is positioned at its turn-over (each rotor model has different turn-over positions), then that rotor and the rotor to its left steps.
  3. No rotor steps more than once per character enciphered.
• There are 3 rotors and they all follow the same procedure, one's output is the next's input.
• The output from the last rotor goes in the Reflector (default to Reflector B) for swapping. Then the backward process starts (from left to right).
• In the end, the Plugboard swaps the character again and output the final character.

Components

Scrambler

Basically, a Scrambler is capable of encrypting a character and forwarding it (right to left) as well as decrypting and "backwarding" it (left to right).

1. Attributes

• flow: each scrambler has different "dictionary" which it uses to translate one character to another.
• offset: some scrambler like Rotor is able to step, so the translation will be changed. Taking the offset into account ensures the correctness of the translation.
• name: helpful for printing.

2. Methods

• foward(char, verbose=1): Forward encrypting a character using the flow. Returns the encrypted character.
• backward(char, verbose=1) Backward encrypting a character using the flow. Return the encrypted character.

Rotor

instance of Scrambler

Each Rotor is a node of a linked-list of rotors in the machine. For further information about the rotor, refer here.

1. Attributes

• model: Each rotor's model will come with different notches and flow. See the full list of rotor types here.
  • notches: When a rotor pass a notch, not only that router shifts, but also its neighbour rotor.
  • flow: see Scrambler.flow.
• next: The next Rotor in the machine. Default to None
• prev: The previous Rotor in the machine. Default to None

2. Methods

• step(): increase the offset by 1. Trigger the next.step() when the rotor is positioned at its notch (known as turn-over).

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TODO

• Reset state of the machine
• Plugboard visualization
• Changable rotor settings
• Start game interface
• Model picking interface
• Turing machine implementation and visualization