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-- ------------------------------------------------------------------------
-- Copyright (C) 2005 Arif Endro Nugroho
-- All rights reserved.
-- 
-- Redistribution and use in source and binary forms, with or without
-- modification, are permitted provided that the following conditions
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-- 
-- 1. Redistributions of source code must retain the above copyright
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-- 2. Redistributions in binary form must reproduce the above copyright
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-- 
-- THIS SOFTWARE IS PROVIDED BY ARIF ENDRO NUGROHO "AS IS" AND ANY EXPRESS
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-- ------------------------------------------------------------------------
 
library ieee;
use ieee.std_logic_1164.all;
use work.xtime_pkg.all;
 
entity mix_column is
 
  port (
    s0          : in  std_logic_vector (07 downto 00);
    s1          : in  std_logic_vector (07 downto 00);
    s2          : in  std_logic_vector (07 downto 00);
    s3          : in  std_logic_vector (07 downto 00);
    mix_col     : out std_logic_vector (31 downto 00);
    inv_mix_col : out std_logic_vector (31 downto 00)
    );
 
end mix_column;
 
architecture data_flow of mix_column is
 
  type state is array (03 downto 00) of std_logic_vector (07 downto 00);
 
  signal mc : state :=
    ( X"00", X"00", X"00", X"00" );
 
begin
 
  --
  -- MixColumn   : a(x)  = {03}x^3 + {01}x^2 + {01}x + {02}
  --
  -- s'0c = | 02 03 01 01 | s0c
  -- s'1c = | 01 02 03 01 | s1c
  -- s'2c = | 01 01 02 03 | s2c
  -- s'3c = | 03 01 01 02 | s3c
  --
  -- InvMixColumn: a'(x) = {0B}x^3 + {0D}x^2 + {09}x + {0E}
  --               a'(x) = {03}x^3 + {01}x^2 + {01}x + {02} +
  --                       {08}x^3 + {08}x^2 + {08}x + {08} +
  --                                 {04}x^2 + {04}x
  --  a(x) * a'(x)     = {01}
  --  a(x) * {a'(x)}^2 = {01} * a'(x) = a'(x)
  --         {a'(x)}^2 = {04}x^2 + {05}
  --
  --              | 05 00 04 00 |          | 0E 0B 0D 09 |   E = 14 = 1110 = 8 xor 4 xor 2 = 1000 xor 0100 xor 0010
  --  {a'(x)}^2 = | 00 05 00 04 |  a'(x) = | 09 0E 0B 0D |   D = 13 = 1101 = 8 xor 4 xor 1 = 1000 xor 0100 xor 0001
  --              | 04 00 05 00 |          | 0D 09 0E 0B |   B = 11 = 1011 = 8 xor 2 xor 1 = 1000 xor 0010 xor 0001
  --              | 00 04 00 05 |          | 0B 0D 09 0E |   9 = 09 = 1001 = 8 xor 0 xor 1 = 1000 xor 0000 xor 0001
  --
 
  mc (3) <= xtime_2(s0) xor xtime_2(s1) xor s1 xor s2 xor s3;
  mc (2) <= s0 xor xtime_2(s1) xor xtime_2(s2) xor s2 xor s3;
  mc (1) <= s0 xor s1 xor xtime_2(s2) xor xtime_2(s3) xor s3;
  mc (0) <= xtime_2(s0) xor s0 xor s1 xor s2 xor xtime_2(s3);
--
  mix_col <= (mc(3) & mc(2) & mc(1) & mc(0));
-- 
  inv_mix_col (31 downto 24) <= xtime_4(mc(3)) xor mc(3) xor xtime_4(mc(1));
  inv_mix_col (23 downto 16) <= xtime_4(mc(2)) xor mc(2) xor xtime_4(mc(0));
  inv_mix_col (15 downto 08) <= xtime_4(mc(1)) xor mc(1) xor xtime_4(mc(3));
  inv_mix_col (07 downto 00) <= xtime_4(mc(0)) xor mc(0) xor xtime_4(mc(2));
--
--   inv_mix_col (31 downto 24) <= 
--                                 xtime_8(mc(3)) xor xtime_4(mc(3)) xor xtime_2(mc(3)) xor 
--                                 xtime_8(mc(2)) xor xtime_2(mc(2)) xor mc(2) xor
--                                 xtime_8(mc(1)) xor xtime_4(mc(1)) xor mc(1) xor
--                                 xtime_8(mc(0)) xor mc(0);
--   inv_mix_col (23 downto 16) <= 
--                                 xtime_8(mc(3)) xor mc(3) xor
--                                 xtime_8(mc(2)) xor xtime_4(mc(2)) xor xtime_2(mc(2)) xor 
--                                 xtime_8(mc(1)) xor xtime_2(mc(1)) xor mc(1) xor
--                                 xtime_8(mc(0)) xor xtime_4(mc(0)) xor mc(0);
--   inv_mix_col (15 downto 08) <= 
--                                 xtime_8(mc(3)) xor xtime_4(mc(3)) xor mc(3) xor
--                                 xtime_8(mc(2)) xor mc(2) xor
--                                 xtime_8(mc(1)) xor xtime_4(mc(1)) xor xtime_2(mc(1)) xor 
--                                 xtime_8(mc(0)) xor xtime_2(mc(0)) xor mc(0);
--   inv_mix_col (07 downto 00) <= 
--                                 xtime_8(mc(3)) xor xtime_2(mc(3)) xor mc(3) xor
--                                 xtime_8(mc(2)) xor xtime_4(mc(2)) xor mc(2) xor
--                                 xtime_8(mc(1)) xor mc(1) xor
--                                 xtime_8(mc(0)) xor xtime_4(mc(0)) xor xtime_2(mc(0));
 
end data_flow;