Subversion Repositories avs_aes

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-- 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)

--

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-- 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:

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--    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

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-- ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE

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-------------------------------------------------------------------------------

-- version management:

-- $Author::                                         $

-- $Date::                                           $

-- $Revision::                                       $

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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;