Class: Key::Wheatstone

Inherits:
SKey show all
Includes:
Crypto
Defined in:
lib/key/wheatstone.rb

Overview

Wheatstone

The Wheatstone cipher (not to be confused with Playfair, also from the author) is a polyalphabetic stream cipher represented by a mechanical device with two synchronized rotors just like a clock called the Wheatstone Cryptograph.

For more details see members.aon.at/cipherclerk/Doc/Whetstone.html www.apprendre-en-ligne.net/crypto/instruments/index.html bit.ly/983rDL

All in all, this is a sliding system where the plain text “wheel/alphabet” slides over repetition of the ciphertext wheel/alphabet.

Constant Summary

BASE = 
'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

Instance Attribute Summary (collapse)

Attributes inherited from SKey

#alpha, #ralpha

Instance Method Summary (collapse)

Methods included from Crypto

#addmod10, #chainadd, #expand5to10, #find_hole, #keyshuffle, #normalize, #p1_encode, #str_to_numeric, #submod10

Constructor Details

- (Wheatstone) initialize(start, plw = BASE, ctw = BASE)

initialize

Either we give full alphabets are keys or just words. In the latter case, generate full alphabets as usual through #keyshuffle



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# File 'lib/key/wheatstone.rb', line 38

def initialize(start, plw = BASE, ctw = BASE)
  super(start)
  if plw.length != BASE.length then
    #
    # Assume plw is a word we use as a base to generate an alphabet with #keyshuffle including space (as +)
    #
    plw = keyshuffle(plw, BASE)
  end
  plw = "+" + plw

  if ctw.length != BASE.length then
    #
    # Assume ctw is a word we use as a base to generate an alphabet with #keyshuffle
    #
    ctw = keyshuffle(ctw, BASE)
  end

  # We use array versions of the keys
  #
  @aplw = plw.each_char.to_a
  @actw = ctw.each_char.to_a

  # We always start at the space (named +) on plaintext
  #
  @curpos = 0

  # Starting letter for ciphertext is not the first one, set ctpos to its position
  #
  @ctpos = ctw.index(start)

  @l_aplw = @aplw.size
  @l_actw = @actw.size
end

Instance Attribute Details

- (Object) actw

Returns the value of attribute actw



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# File 'lib/key/wheatstone.rb', line 29

def actw
  @actw
end

- (Object) aplw

Returns the value of attribute aplw



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# File 'lib/key/wheatstone.rb', line 29

def aplw
  @aplw
end

- (Object) ctpos

Returns the value of attribute ctpos



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# File 'lib/key/wheatstone.rb', line 29

def ctpos
  @ctpos
end

- (Object) curpos

Returns the value of attribute curpos



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# File 'lib/key/wheatstone.rb', line 29

def curpos
  @curpos
end

Instance Method Details

- (Object) decode(c) 



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# File 'lib/key/wheatstone.rb', line 85

def decode(c)
  a = @actw.index(c)
  if a <= @ctpos
    # we have made a turn
    off = (a + @l_actw) - @ctpos
  else
    off = a - @ctpos
  end
  @ctpos = a
  @curpos = (@curpos + off) % @l_aplw
  @aplw[@curpos]
end

- (Object) encode(c)

– initialize



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# File 'lib/key/wheatstone.rb', line 72

def encode(c)
  a = @aplw.index(c)
  if a <= @curpos
    # we have made a turn
    off = (a + @l_aplw) - @curpos
  else
    off = a - @curpos
  end
  @curpos = a
  @ctpos = (@ctpos + off) % @l_actw
  @actw[@ctpos]
end