xor_method_for_string.rb

#!/usr/bin/ruby
#
# Stringクラスにxor(^)を追加してみるテスト。主にCTF用？
#
class String
  def ^(str)
    sho = self
    lon = str
    sho, lon = lon, sho if sho.size > lon.size

    (0...lon.size).inject("") {|r,i| r + (lon[i] ^ sho[i % sho.size]).chr}
  end

  def hexdump
    (0...self.size).inject("") {|r,i| r + ("%02x "%self[i]) }
  end
end

a = "\x01\x23\x45\x67\x89\xab\xcd\xef"
b = "\x76\x54\x32\x10"

c = a ^ b
puts c.hexdump  # => "\x77\x77\x77\x77\xFF\xFF\xFF\xFF"