Ruby Quellcode

#==============================================================================
# ** RC4 (aka ARC4 and ARCFOUR)
#------------------------------------------------------------------------------
#  Authors: Cremno (Ruby implentation), Ronald L. Rivest (developer of RC4)
#  Date:    16-09-2008 06:12 (dd-mm-hh hh::mm GMT +01:00)
#  Thanks:  Jason Cooper (for a great RC4 Tutorial), Wikipedia
#------------------------------------------------------------------------------
#  With this snippet you can en- and decrypt strings to/from RC4.
#==============================================================================
 
class String
  #--------------------------------------------------------------------------
  # * En- and decrypts to RC4 (Original by Ronald L. Rivest)
  #--------------------------------------------------------------------------
  # Usage:
  #  <string>.rc4(<Key>) => en- or decrypted string
  # Examples:
  #  "24z2".rc4("24g3") => "nhnU"
  #  "nhnU".rc4("24g3") => "24z2"
  #--------------------------------------------------------------------------
  def rc4(_key)
    _cipher = ""
    _size = 256
    _sbox = Array.new(_size){|i| i}
    # fill keybox
    _kbox = (_key * _size).slice(0, _size).unpack("C*")
    # prepare substitionbox
    _j = 0
    _size.times{|i|
      _j = (_j + _sbox[i] + _kbox[i]) % _size
      _sbox[i], _sbox[_j] = _sbox[_j], _sbox[i]
    }
    # crypt text
    _i = _j = 0
    length().times{|z|
      _i = _i.next() % _size
      _j = (_j + _sbox[_i]) % _size
      _sbox[_i], _sbox[_j] = _sbox[_j], _sbox[_i]
      _in = (_sbox[_i] + _sbox[_j]) % _size
      _cipher << (slice(z) ^ _sbox[_in])
    }
    _cipher
  end
end