#
#--
# Ronin - A Ruby platform designed for information security and data
# exploration tasks.
#
# Copyright (c) 2006-2009 Hal Brodigan (postmodern.mod3 at gmail.com)
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
#++
#

require 'ronin/translators/translator'
require 'ronin/chars'

module Ronin
  module Translators
    class XOR < Translator

      # Set of characters to allow in the encoded data
      attr_accessor :allow

      #
      # Creates a new XOR Translator object using the given _options_.
      # If a _block_ is given it will be passed the newly created
      # Translator object.
      #
      # _options_ may include the following keys:
      # <tt>:allow</tt>:: The set of characters allowed in the encoded
      #                   result. Defaults to <tt>(1..255)</tt>.
      # <tt>:disallow</tt>:: The set of characters that are not allowed
      #                      in the encoded result.
      #
      def initialize(options={},&block)
        @allow = Chars::CharSet.new(options[:allow] || (1..255))

        if options[:disallow]
          @allow -= options[:disallow]
        end

        super(&block)
      end

      #
      # XOR encodes the specified _data_ prefixing the XOR key to the
      # encoded data. If a _block_ is given, it will be passed the encoded
      # data.
      #
      def encode(data,&block)
        alphabet = Chars.all.select { |b| data.include?(b.chr) }
        excluded = (Chars.all - alphabet)

        key = excluded.select { |b|
          @allow.include?(b) && alphabet.all? { |i|
            @allow.include?(i ^ b)
          }
        }.last

        text = ''

        text << key.chr
        data.each_byte { |b| text << (b ^ key).chr }

        block.call(text) if block
        return text
      end

      #
      # XOR decodes the specified _text_. If a _block_ is given, it will be
      # passed the decoded data.
      #
      def decode(text,&block)
        data = ''
        key = text[0]
        
        text[1..-1].each_byte do |b|
          data << (b ^ key).chr
        end

        return data
      end

    end
  end
end