Class: Cipher::Transposition

Inherits:
SimpleCipher show all
Defined in:
lib/cipher.rb

Overview

Transposition

Plain Transposition aka transposition

Instance Method Summary (collapse)

Constructor Details

- (Transposition) initialize(key)

Returns a new instance of Transposition



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# File 'lib/cipher.rb', line 20

def initialize(key)
  @key = Key::TKey.new(key)
end

Instance Method Details

- (Object) decode(cipher_text)

decode



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# File 'lib/cipher.rb', line 51

def decode(cipher_text)
  #
  # Look whether we are square or not
  #
  text = cipher_text.dup
  t_len = @key.length
  pad = text.length % t_len
  #
  # if pad is non-zero, last line is not finished by pad i.e.
  # columns pad-1 .. t_len-1 are shorter by 1
  #
  t_height = (text.length / t_len) + 1
  table = Array.new(t_len) { '' }
  plain_text = ''
  
  #puts "#{text.length} #{pad} #{t_height}"
  tkey = @key.to_numeric
  #
  # Fill in transposition board
  #
  for i in 0..(t_len - 1) do
    ind = tkey.index(i)
    how_many = t_height
    if ind > pad - 1 then
      how_many -= 1
    end
    ct = text.slice!(0, how_many)
    table[ind] << ct
    #puts "#{ct} #{how_many} #{ind} #{i}"
  end
  #
  # Now take the plain text
  #
  for j in 0..(t_height - 1) do
    for i in 0..(t_len - 1) do
      col = table[i]
      plain_text << (col[j] || '')
    end
  end
  return plain_text
end

- (Object) encode(plain_text)

encode



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# File 'lib/cipher.rb', line 26

def encode(plain_text)
  #
  j = 0
  t_len = @key.length
  table = Array.new(t_len) { '' }
  cipher_text = ''
  
  tkey = @key.to_numeric
  #
  # XXX String.scan in 1.9, #each_byte?
  #
  plain_text.scan(/./) do |pt|
    table[tkey[j]] << pt
    j = (j + 1) % t_len
  end
  #
  # Now take every column based upon key ordering
  #
  cipher_text = tkey.sort.each.inject('') do |text, t|
    text +  table[t]
  end
end