suryart/spree_ebsin

module SpreeEbsin
  class RC4

    def initialize(str)
      begin
        raise SyntaxError, "RC4: Key supplied is blank"  if str.eql?('')

        @q1, @q2 = 0, 0
        @key = []
        str.each_byte {|elem| @key << elem} while @key.size < 256
        @key.slice!(256..@key.size-1) if @key.size >= 256
        @s = (0..255).to_a
        j = 0 
        0.upto(255) do |i| 
          j = (j + @s[i] + @key[i] )%256
          @s[i], @s[j] = @s[j], @s[i]
        end    
      end
    end
    
    def encrypt!(text)
      process text
    end  
    
    def encrypt(text)
      process text.dup
    end 

    alias_method :decrypt, :encrypt
    
    private

      def process(text)
        text.unpack("C*").map { |c| c ^ round }.pack("C*")
      end
      
      def round
        @q1 = (@q1 + 1)%256
        @q2 = (@q2 + @s[@q1])%256
        @s[@q1], @s[@q2] = @s[@q2], @s[@q1]
        @s[(@s[@q1]+@s[@q2])%256]  
      end
  end
end