enigma_machine.rb

Plugboard = Hash[*('A'..'Z').to_a.shuffle.first(20)]
Plugboard.merge!(Plugboard.invert)
Plugboard.default_proc = proc { |hash, key| key }

def build_a_rotor
  Hash[('A'..'Z').zip(('A'..'Z').to_a.shuffle)]
end

Rotor_1, Rotor_2, Rotor_3 = build_a_rotor, build_a_rotor, build_a_rotor

Reflector = Hash[*('A'..'Z').to_a.shuffle]
Reflector.merge!(Reflector.invert)

def input(string)
  rotor_1, rotor_2, rotor_3 = Rotor_1.dup, Rotor_2.dup, Rotor_3.dup

  string.chars.each_with_index.map do |char, index|
    rotor_1 = rotate_rotor rotor_1
    rotor_2 = rotate_rotor rotor_2 if index % 25 == 0
    rotor_3 = rotate_rotor rotor_3 if index % 25*25 == 0

    char = Plugboard[char]

    char = rotor_1[char]
    char = rotor_2[char]
    char = rotor_3[char]

    char = Reflector[char]

    char = rotor_3.invert[char]
    char = rotor_2.invert[char]
    char = rotor_1.invert[char]

    Plugboard[char]
  end.join
end

def rotate_rotor(rotor)
  Hash[rotor.map { |k,v| [k == 'Z' ? 'A' : k.next, v] }]
end

plain_text = 'IHAVETAKENMOREOUTOFALCOHOLTHANALCOHOLHASTAKENOUTOFME'
puts "Encrypted '#{plain_text}' to '#{encrypted = input(plain_text)}'"
puts "Decrypted '#{encrypted}' to '#{decrypted = input(encrypted)}'"
puts 'Success!' if plain_text == decrypted