class RotorMachine::Machine

The {RotorMachine::Machine} class serves as the entrypoint and orchestrator for an Enigma machine.

Components of an Enigma machine

The Enigma machine, as represented by the RotorMachine module, consists of the following components:

On an actual Enigma machine, these components are all electromechanical, and the Enigma also included a keyboard, a grid of lights to show the results, and in some cases a printer. Since this is a simulated Enigma, obviously, no keyboard/printer are supplied here.

The polyalphabetic encryption of the Enigma comes from the fact that the rotors are linked (mechanically in a real Enigma) so that they rotate one or more “steps” after each character, changing the signal paths and transpositions. This means that a sequence of the same plaintext character will encipher to different ciphertext characters.

The rotors are designed to advance such that each time a rotor completes a full revolution, it will advance the rotor to its left once. The rotors allow you to configure how many positions they advance when they do. So, assuming all rotors are advancing one position at a time, if the rotors have position “AAZ”, their state after the next character is typed will be “ABA”.

To learn much more about the inner workings of actual Enigma machines, visit {en.wikipedia.org/wiki/Enigma_machine}.

The Signal Path of Letters

On a physical Enigma machine, the electrical signal from a keypress is routed through the plugboard, then through each of the rotors in sequence from left to right. The signal then passes through the reflector (where it is transposed again), then back through the rotors in reverse order, and finally back through the plugboard a second time before being displayed on the light grid and/or printer.

One important consequence of this signal path is that encryption and decryption are the same operation. That is to say, if you set the rotors and plugboard, and then type your plaintext into the machine, you'll get a string of ciphertext. If you then reset the machine to its initial state and type the ciphertext characters into the machine, you'll produce your original plaintext.

One consequence of the Enigma's design is that a plaintext letter will never encipher to itself. The Allies were able to exploit this property to help break the Enigma's encryption in World War II.

Usage

To use the RotorMachine Enigma machine, you need to perform the following steps:

  1. Create a new {RotorMachine::Machine} object.

  2. Add one or more {RotorMachine::Rotor Rotors} to the `rotors` array.

  3. Set the `reflector` to an instance of the {RotorMachine::Reflector Reflector} class.

  4. Make any desired connections in the {RotorMachine::Plugboard Plugboard}.

  5. Optionally, set the rotor positions with {#set_rotors}.

You're now ready to encipher and decipher your text using the {#encipher} method to encode/decode, and {#set_rotors} to reset the machine state.

The {#default_machine} and {#empty_machine} class methods are shortcut factory methods whcih set up, respectively, a fully configured machine with a default set of rotors and reflector, and an empty machine with no rotors or reflector.

Attributes

plugboard[RW]
reflector[RW]
rotors[RW]

Public Class Methods

default_machine() click to toggle source

Generates a default-configuration RotorMachine, with the following state:

  • Rotors I, II, III, each set to A and configured to advance a single step at a time

  • Reflector A

  • An empty plugboard with no connections

This method is just a proxy for the equivalently-named factory method in the {RotorMachine::Factory} class, and is maintained here for backward compatibility.

# File lib/rotor_machine/machine.rb, line 106
def self.default_machine
  RotorMachine::Factory.default_machine
end
empty_machine() click to toggle source

Generates an empty-configuration RotorMachine, with the following state:

  • No rotors

  • No reflector

  • An empty plugboard with no connections

A RotorMachine in this state will raise an {ArgumentError} until you outfit it with at least one rotor and a reflector.

This method is just a proxy for the equivalently-named factory method in the {RotorMachine::Factory} class, and is maintained here for backward compatibility.

# File lib/rotor_machine/machine.rb, line 124
def self.empty_machine
  RotorMachine::Factory.empty_machine()
end
from_yaml(config) click to toggle source

Create a new {RotorMachine::Machine} from a YAML configuration file.

This class method is a one-step shortcut for creating an empty {RotorMachine::Machine} and then loading its machine state.

@param config [Hash] A configuration hash for the new machine, such as a config hash generated by {#machine_state}. @return [RotorMachine::Machine] A new {RotorMachine::Machine} created from the supplied config hash.

# File lib/rotor_machine/machine.rb, line 313
def self.from_yaml(config)
  unless config.keys.include?(:serialization_version)
    raise ArgumentError, "Serialization Data Version Mismatch"
  end
  unless config[:serialization_version].is_a?(Numeric)
    raise ArgumentError, "Serialization Data Version Mismatch"
  end
  if (config[:serialization_version] > RotorMachine::VERSION_DATA[0]) || (config[:serialization_version] < 1)
    raise ArgumentError, "Serialization Data Version Mismatch"
  end

  m = self.empty_machine
  m.set_machine_config_from(config)
  return m
end
new() click to toggle source

Initialize a RotorMachine object.

This object won't be usable until you add rotors, a reflector and a plugboard. Using the {#default_machine} and {#empty_machine} helper class methods is the preferred way to initialize functioning machines.

# File lib/rotor_machine/machine.rb, line 88
def initialize()
  @rotors = []
  @reflector = nil
  @plugboard = nil
end

Public Instance Methods

==(another_machine) click to toggle source

Compare another {RotorMachine::Machine} instance to this one.

Returns true if the provided {RotorMachine::Machine} has the same configuration as this one, and false otherwise.

@param another_machine [RotorMachine::Machine] The Machine to compare to this one. @return [Boolean] True if the machines have identical configuration, false otherwise.

# File lib/rotor_machine/machine.rb, line 385
def ==(another_machine)
  @rotors == another_machine.rotors &&
    @reflector == another_machine.reflector &&
    @plugboard == another_machine.plugboard
end
encipher(text) click to toggle source

Encipher (or decipher) a string.

Each character of the string is, in turn, passed through the machine. This process is documented in the class comment for the {RotorMachine::Machine} class.

Because the Enigma machine did not differentiate uppercase and lowercase letters, the source string is upcase'd before processing. @param text [String] the text to encipher or decipher @return [String] the enciphered or deciphered text

# File lib/rotor_machine/machine.rb, line 139
def encipher(text)
  raise ArgumentError, "Cannot encipher; no rotors loaded" if (@rotors.count == 0)
  raise ArgumentError, "Cannot encipher; no reflector loaded" if (@reflector.nil?)
  text.upcase.chars.collect { |c| self.encipher_char(c) }.join("").in_blocks_of(5)
end
encipher_char(c) click to toggle source

Encipher a single character.

Used by {#encipher} to walk a single character of text through the signal path of all components of the machine.

@param c [String] a single-character string containing the next

character to encipher/decipher

@return [String] the enciphered/deciphered character. After the

character passes through the machine, a call is made to
{#step_rotors} to advance the rotors.
# File lib/rotor_machine/machine.rb, line 201
def encipher_char(c)
  ec = c

  unless @plugboard.nil?
    ec = @plugboard.transpose(ec)
  end

  @rotors.each { |rotor| ec = rotor.forward(ec) }
  ec = @reflector.reflect(ec)
  @rotors.reverse.each { |rotor| ec = rotor.reverse(ec) }

  unless @plugboard.nil?
    ec = @plugboard.transpose(ec)
  end

  unless ec == c
    self.step_rotors
  end
  ec
end
load_machine_state_from(filepath) click to toggle source

Read the internal machine state from a YAML file.

The YAML file can be created using the #{save_machine_state_to} method to save the machine state of an existing {RotorMachine::Machine} object.

The internal state is captured as is, so if you save the state from a machine that's not validly configured (no rotors, no reflector, etc.), the reconstituted machine will also have an invalid state.

@param filepath [String] The path to the YAML file to which the machine state should be saved.

# File lib/rotor_machine/machine.rb, line 296
def load_machine_state_from(filepath)
  raise ArgumentError, "File path \"#{filepath}\" not found!" unless File.exist?(filepath)
  c = YAML.load(File.open(filepath))
  self.set_machine_config_from(c)
  return true
end
machine_state() click to toggle source

Create a Ruby hash containing a snapshot of the current machine state.

The hash returned by this method contains enough information to capture the current internal state of the machine. Although you can invoke it directly if you want to, it is primarily intended to be accessed via the {#save_machine_state_to} and {#load_machine_state_from} methods, which save and load machine state to YAML files.

@return [Hash] A Hash representing the internal state of the machine.

# File lib/rotor_machine/machine.rb, line 232
def machine_state
  machine_state = {}
  machine_state[:serialization_version] = RotorMachine::VERSION_DATA[0]

  machine_state[:rotors] = []
  self.rotors.each do |r|
    rstate = {
      kind: r.rotor_kind_name,
      position: r.position,
      step_size: r.step_size
    }
    if r.rotor_kind_name == :CUSTOM
      rstate[:letters] = r.rotor_kind
    end

    machine_state[:rotors] << rstate
  end
  machine_state[:reflector] = {
    kind: self.reflector.reflector_kind_name,
    position: self.reflector.position
  }
  if (self.reflector.reflector_kind_name == :CUSTOM)
    machine_state[:reflector][:letters] = self.reflector.letters
  end

  machine_state[:plugboard] = {
    connections: self.plugboard.connections.clone
  }
  return machine_state
end
save_machine_state_to(filepath) click to toggle source

Write the internal machine state to a YAML file.

The generated YAML file can be loaded using the #{load_machine_state_from} method to restore a saved machine state.

@param filepath [String] The path to the YAML file to which the machine state should be saved. @return [Boolean] True if the save operation completed successfully, false if an error was raised.

# File lib/rotor_machine/machine.rb, line 273
def save_machine_state_to(filepath)
  begin
    File.open(filepath, "w") do |f|
      f.puts machine_state.to_yaml
    end
    return true
  rescue
    return false
  end
end
set_machine_config_from(config) click to toggle source

Set the state of the machine based on values in a config hash.

Any config hash (such as that generated by {#machine_state}) can be provided as an argument, but this method is primarily intended to be accessed by the {#from_yaml} and {#load_config_state_from} methods to deserialize a machine state hash.

@param config [Hash] The configuration hash describing the state of the {RotorMachine::Machine}. @return [RotorMachine::Machine] The {RotorMachine::Machine} which was just configured. def set_machine_config_from(config)

# File lib/rotor_machine/machine.rb, line 341
def set_machine_config_from(config)
  @rotors = []
  @reflector = nil
  @plugboard = RotorMachine::Plugboard.new()

  # Create rotors
  config[:rotors].each do |rs|
    if rs[:kind] == :CUSTOM
      r = RotorMachine::Rotor.new(rs[:letters], rs[:position], rs[:step_size])
    else
      letters = RotorMachine::Rotor.const_get(rs[:kind])
      r = RotorMachine::Rotor.new(letters, rs[:position], rs[:step_size])
    end
    @rotors << r
  end

  # Create reflector
  if config[:reflector][:kind] == :CUSTOM
    letters = config[:reflector][:letters]
  else
    letters = RotorMachine::Reflector.const_get(config[:reflector][:kind])
  end
  @reflector = RotorMachine::Reflector.new(letters, config[:reflector][:position])

  # Plugboard mappings
  config[:plugboard][:connections].keys.each do |l|
    unless @plugboard.connected?(l)
      @plugboard.connect(l, config[:plugboard][:connections][l])
    end
  end

  return self
end
set_rotors(init_val) click to toggle source

Set the initial positions of the set of rotors before begining an enciphering or deciphering operation.

This is a helper method to avoid having to manipulate the rotor positions individually. Starting with the leftmost rotor, each character from this string is used to set the position of one rotor.

If the string is longer than the number of rotors, the extra values (to the right) are ignored. If it's shorter, the values of the “extra” rotors will be unchanged.

@param init_val [String] A string containing the initial values for the rotors.

# File lib/rotor_machine/machine.rb, line 170
def set_rotors(init_val)
  init_val.chars.each_with_index do |c, i|
    @rotors[i].position = c if (i < @rotors.length)
  end
end
step_rotors() click to toggle source

Coordinate the stepping of the set of rotors after a character is enciphered.

# File lib/rotor_machine/machine.rb, line 148
def step_rotors
  @rotors.reverse.each do |rotor|
    rotor.step
    break unless rotor.wrapped?
  end
end
to_s() click to toggle source

Describe the current state of the machine in human-readable form.

@return [String] A description of the Rotor Machine's current internal state.

# File lib/rotor_machine/machine.rb, line 181
def to_s
  buf = "a RotorMachine::Machine with the following configuration:\n"
  buf += "  Rotors: #{@rotors.count}\n"
  @rotors.each { |r| buf += "    - #{r.to_s}\n" }
  buf += "  Reflector: #{@reflector.nil? ? "none" : @reflector.to_s}\n"
  buf += "  Plugboard: #{@plugboard.nil? ? "none" : @plugboard.to_s}"
  return buf
end