-------------------------------------------------------------------------------
-- A Geffe Keystream Generator
-- Author       : Tam Paredes
-- File Name    : key_generator.vhd
-- Architecture : structural
-- Description  : This keystream generator uses three LFSRs combined
--				  nonlinearly.  Two LFSRs are inputs, while the third LFSR
--				  controls the output of the multiplexer.
-------------------------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;
library work;
use work.stream_cipher_pkg.all;

entity key_generator is
	port(clock,reset,enable :	in std_logic;
		 output				:	out std_logic
		);
end key_generator;

architecture structural of key_generator is

signal  internal_LFSR1,
		internal_LFSR2,
		internal_LFSR3: std_logic;

begin

	LFSR1: shift_reg13
		port map(clock => clock,
				 reset => reset,
				 enable => enable,
				 output => internal_LFSR1
				);


	LFSR2: shift_reg11
		port map(clock => clock,
				 reset => reset,
				 enable => enable,
				 output => internal_LFSR2
				);


	LFSR3: shift_reg8
		port map(clock => clock,
				 reset => reset,
				 enable => enable,
				 output => internal_LFSR3
				);

	Mux2to1: mux2_1
		port map(inputA => internal_LFSR2,
            	 inputB => internal_LFSR3,
           	 	 sel    => internal_LFSR1,
          	 	 output => output
    			);

end structural;