Encrypt messages using the Enigma machine (TUI version)

The Enigma is a machine extensively used by the Nazi Germany Armed Forces during World War II.
It enciphers messages using an electromechanical mecanism that consists in:

• 1 keyboard;
• 1 plugboard, connecting 10 pairs of letters;
• 3 rotors;
• 1 reflector;
• 26 lights that shows the enciphered letter.

Similar to a typing machine keyboard.
After pressing a key, an electrical signal is passed to the plugboard, where the letter could be scrambled.

A board in the machine's front side, containing a socket for each alphabet letter, wired to the respective keyboard key.
Ten pair of letter are chosen to be plugged, swapping the letter if a signal is received, i.e. if 'A' and 'B' are connected in the plugboard and 'A' is pressed on the keyboard, the output would be 'B'.

The rotors are wheels with two faces, one containing, for each letter in the alphabet, contact pins to pass an electrical signal and the other containing metallic plates to receive this signal.
Each pin and plate represent a letter; the input letter is scrambled by connecting the pin that represents it to a plate that represents another letter. There are a few different types of rotors, each wiring the faces in different ways.
The rotor also has a mechanism that makes its wheels rotate after each time the keyboard is press, reconnecting the faces in a different setting, so if the same letter is pressed multiple times, the enciphered message will have different letters, making the code harder to crack.
Regular Enigma machines have 3 rotors connected side by side, but only the rightmost rotates.
Each rotor model has a notch in a different key; the left side rotor will only move when the mechanism that rotates the wheels (a ratchet with pawls) pushes the notch, making both rotors step together.

Similar to a rotor, but doesn't rotate nor has anything connected to its left.
The reflector receives the electrical signal from the last rotor, passes to its other face and, instead of sending to a next component, it passes it back to its first face, sending to the last rotor again.

After pressing any keyboard key, the rotor steps, then:

• The signal goes to the plugboard, which might scramble the letter once, then sends it to the rightmost rotor;
• The signal goes through its wiring, scrambling the letter when it reaches the rotors other face. Then, it is passed to the middle rotor;
• The last step repeats, then again in the left rotor, where the signal is passed to the reflector;
• There, the letter is scramble again and the signal is passed back to the rotors, repeating the process;
• After passing backwards through the right rotor, the signal is sent back to the plugboard, where the letter might be swapped once more;
• Finally, the plugboard send the letter to the lights, showing the user the enciphered letter.

This application is based on the German Army and Air Force version of Enigma, which has a set of five rotors to be chosen, one reflector and connects ten pairs of letters in the plugboard.
To calculate the number of possible settings, it's necessary to know how many ways are there to arrange each of the components.

First, the rotors:

• Choose three out of five, without repetition: $5! = 60$ possibilities
• Choose each rotor's initial position relative to its wiring: $26^{3} = 17,576$ possibilities
• Total rotors settings: 1,054,560

Then, the plugboard:

• Choose the order to plug all of the letters: $26!$ possibilities
• Choose the six letters that won't be connected: $6!$ possibilities
• Choose how the 10 wires are going to connect the 20 plugs: $10!$ possibilities
• Disconsider the order each extremity of the same wire is connected (as they are equivalent), for all ten wires: $2^{10} = 1024$
• Total plugboard settings: $\frac{26!}{6! * 10! * 1024} = 150,738,274,937,250$

Multiplying each result gives the total possible arrengements:
$1,054,560 * 150,738,274,937,250 = 158,962,555,217,826,360,000$

In this application, however, the user can also choose a reflector from a list (its initial position is fixed):

• Choose one reflector out of five: 5 possibilities

Multiplying this by the former total:
$158,962,555,217,826,360,000 * 5 = 794,812,776,089,131,800,000$ possible arrangements

It can be easily built using CMake:

First, clone the source code (or download the .zip file):

git clone https://github.com/KaueMiziara/k-enigma-tui.git

Then, open the directory in the terminal and use cmake to build the executable:

cd path/to/directory

# This will create a 'build' folder and generate the buildsystem
cmake -S . -B build

# This will build the project using the generated buildsystem
cmake --build build

The executable will be inside the 'build' folder.

To choose the letter pairs connected in the plugboard, edit the file 'PlugboardSettings.txt'.

• Each line is expected to have a pair of letters.
  
• If there are more than two letters in a single line, they will be ignored.
  
• If a non ASCII-alphabetic character is found, it will be replaced by the letter 'A'.
  
• If there is a single letter in a line, it will be matched with 'A'.
  

Just run the executable file from the terminal:

$ cd /path/to/project/folder/
$ ./build/enigma-tui

# Choose the rotors and the respective initial position
(1/3) What rotor should be used?
Rotor list: 'I', 'II', 'III', 'IV', 'V', default: 'I'
$ (input left rotor)
(1/3) What should be the rotor initial position?
Default: 'A'
$ (input a letter)

(2/3) What rotor should be used?
Rotor list: 'I', 'II', 'III', 'IV', 'V', default: 'I'
$ (input middle rotor)
(2/3) What should be the rotor initial position?
Default: 'A'
$ (input a letter)

(3/3) What rotor should be used?
Rotor list: 'I', 'II', 'III', 'IV', 'V', default: 'I'
$ (input right rotor)
(3/3) What should be the rotor initial position?
Default: 'A'
$ (input a letter)

# Choose the reflector
What reflector should be used?
Reflector list: 'A', 'B', 'C', 'Beta', 'Gamma', default: 'A'
$ (input reflector)

# Prints the wiring for the chosen rotors and reflector
Leftmost rotor wiring: ..., notch: ...
Middle rotor wiring: ..., notch: ...
Rightmost rotor wiring: ..., notch: ...

Reflector wiring: ...

Plugboard settings: ...

# Machine keyboard input
Insert a text:
$ (input text to be enciphered)

Rotor and reflector models differentiate from each other by their wiring.
Below, a list of the availabe models, the respective wiring and where is the notch (for rotors).

• "I": "EKMFLGDQVZNTOWYHXUSPAIBRCJ", notch: 'Q'
• "II": "AJDKSIRUXBLHWTMCQGZNPYFVOE", notch: 'E'
• "III": "BDFHJLCPRTXVZNYEIWGAKMUSQO", notch: 'V'
• "IV": "ESOVPZJAYQUIRHXLNFTGKDCMWB", notch: 'J'
• "V": "VZBRGITYUPSDNHLXAWMJQOFECK", notch: 'Z'

• "A": "EJMZALYXVBWFCRQUONTSPIKHGD"
• "B": "YRUHQSLDPXNGOKMIEBFZCWVJAT"
• "C": "FVPJIAOYEDRZXWGCTKUQSBNMHL"
• "β": "LEYJVCNIXWPBQMDRTAKZGFUHOS"
• "γ": "FSOKANUERHMBTIYCWLQPZXVGJD"