Subversion Repositories avs_aes

--------------------------------------------------------------------------------
-- This file is part of the project  avs_aes
-- see: http://opencores.org/project,avs_aes
--
-- description: DECRYPTION implementation of Shift row.
-- Shift Row rotates the Rows of the AES Block
-- This module takes the whole Rijdael state as input, extracts the rows,
-- shifts them and rebuilts the state.
--
-------------------------------------------------------------------------------
--
-- Author(s):
--	   Thomas Ruschival -- ruschi@opencores.org (www.ruschival.de)
--
--------------------------------------------------------------------------------
-- Copyright (c) 2009, Authors and opencores.org
-- All rights reserved.
--
-- Redistribution and use in source and binary forms, with or without modification,
-- are permitted provided that the following conditions are met:
--    * Redistributions of source code must retain the above copyright notice,
--    this list of conditions and the following disclaimer.
--    * Redistributions in binary form must reproduce the above copyright notice,
--    this list of conditions and the following disclaimer in the documentation
--    and/or other materials provided with the distribution.
--    * Neither the name of the organization nor the names of its contributors
--    may be used to endorse or promote products derived from this software without
--    specific prior written permission.
-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-- AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-- IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-- ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
-- LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
-- OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-- SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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-- ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
-- THE POSSIBILITY OF SUCH DAMAGE
-------------------------------------------------------------------------------
-- version management:
-- $Author$
-- $Date$
-- $Revision$			
-------------------------------------------------------------------------------
library IEEE;
use IEEE.numeric_std.all;
use IEEE.std_logic_1164.all;
 
library avs_aes_lib;
use avs_aes_lib.avs_aes_pkg.all;
 
 
architecture inv of Shiftrow is
	-- type of converting the columns into rows
	subtype ROW is BYTEARRAY(0 to 3);
 
	-- Row signal for easier handling of the shift operations
	signal row1_in	: Row;				-- 1st row
	signal row2_in	: Row;				-- 2nd row
	signal row3_in	: Row;				-- 3rd row
	signal row4_in	: Row;				-- 4th row
	-- single rows after shift operation
	-- row1 of the shifted state = row1 of unshifted state 
	signal row2_out : Row;				-- 2nd row
	signal row3_out : Row;				-- 3rd row
	signal row4_out : Row;				-- 4th row
 
begin  -- architecture arch1
	-- purpose: build the temorary internal signals for easier handling
	-- type	  : combinational
	-- inputs : state_in
	-- outputs: state_out
	build_in : process (state_in) is
	begin  -- process build_in
		-- state is a DWORD array with 32 Byte in 4 columns
		-- thus we loop through the columns and slice the column in its bytes
		for col_cnt in 0 to (state_in'high) loop
			row1_in(col_cnt) <= state_in(col_cnt)(31 downto 24);
			row2_in(col_cnt) <= state_in(col_cnt)(23 downto 16);
			row3_in(col_cnt) <= state_in(col_cnt)(15 downto 8);
			row4_in(col_cnt) <= state_in(col_cnt)(7 downto 0);
		end loop;  -- col_cnt
	end process build_in;
 
 
	-- purpose: Undo the shifting of rows
	-- type	  : combinational
	-- inputs : row(1 to 4)_in
	-- outputs: row(1 to 4)_out
	shifter : process (row2_in, row3_in, row4_in) is
	begin
		-- row2 is always shifted by one cell
		row2_out <= row2_in(row2_in'right) & row2_in(row2_in'left to row2_in'right-1);
		-- row3 is shifted by two
		row3_out <= row3_in(row3_in'right-1 to row3_in'right) & row3_in(row3_in'left to row3_in'right-2);
		-- rotate by 3 right
		row4_out <= row4_in(row4_in'right-2 to row4_in'right) & row4_in(row4_in'left to row4_in'right-3);
	end process shifter;
 
 
	-- purpose: rebuilt the state form the shifted rows
	-- type	  : combinational
	-- inputs : row1_out, row2_out, row3_out, row4_out
	-- outputs: state_out
	rebuilt_state : process (row1_in, row2_out, row3_out, row4_out) is
	begin  -- process rebuilt_state 
		for col_cnt in 0 to state_out'high loop	 -- works because 15/4=3
			state_out(col_cnt)(31 downto 24) <= row1_in(col_cnt);
			state_out(col_cnt)(23 downto 16) <= row2_out(col_cnt);
			state_out(col_cnt)(15 downto 8)	 <= row3_out(col_cnt);
			state_out(col_cnt)(7 downto 0)	 <= row4_out(col_cnt);
		end loop;  -- col_cnt		
	end process rebuilt_state;
 
end architecture inv;