Subversion Repositories aes_decrypt_fpga

////////////////////////////////////////////////////////////////// ////

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//// AES Decryption Core for FPGA                                                                       ////

////                                                                                                                            ////

//// This file is part of the AES Decryption Core for FPGA project      ////

//// http://www.opencores.org/cores/xxx/                                                        ////

////                                                                                                                            ////

//// Description                                                                                                        ////

//// Implementation of  AES Decryption Core for FPGA according to       ////

//// core specification document.                                                                       ////

////                                                                                                                            ////

//// To Do:                                                                                                             ////

//// -                                                                                                                          ////

////                                                                                                                            ////

//// Author(s):                                                                                                         ////

//// - scheng, schengopencores@opencores.org                                            ////

////                                                                                                                            ////

//////////////////////////////////////////////////////////////////////

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//// Copyright (C) 2009 Authors and OPENCORES.ORG                                       ////

////                                                                                                                            ////

//// This source file may be used and distributed without                       ////

//// restriction provided that this copyright statement is not          ////

//// removed from the file and that any derivative work contains        ////

//// the original copyright notice and the associated disclaimer.       ////

////                                                                                                                            ////

//// This source file is free software; you can redistribute it         ////

//// and/or modify it under the terms of the GNU Lesser General         ////

//// Public License as published by the Free Software Foundation;       ////

//// either version 2.1 of the License, or (at your option) any         ////

//// later version.                                                                                             ////

////                                                                                                                            ////

//// This source is distributed in the hope that it will be             ////

//// useful, but WITHOUT ANY WARRANTY; without even the implied         ////

//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR            ////

//// PURPOSE. See the GNU Lesser General Public License for more        ////

//// details.                                                                                                           ////

////                                                                                                                            ////

//// You should have received a copy of the GNU Lesser General          ////

//// Public License along with this source; if not, download it         ////

//// from http://www.opencores.org/lgpl.shtml                                           ////

////                                                                                                                            //// ///

///////////////////////////////////////////////////////////////////

////                                                                                                                            ////

//// This module implements the Galois field multipliers                        ////

//// for x2, x3, x9, xb, xd, xe. Used in InvMixCol_slice.                       ////

//// See section 4.2 of FIPS-197 specification for details.                     ////

////                                                                                                                            ////

////////////////////////////////////////////////////////////////////////

module gfmul_inv(

        input   [7:0]   d,

        output  [7:0]   x2,

        output  [7:0]   x3,

        output  [7:0]   x9,

        output  [7:0]   xb,

        output  [7:0]   xd,

        output  [7:0]   xe

        );

        // Multiplier over GF(256)

        // Generates -  x2, 3 for cipher

        //                       -      x9, xb, xd, xe for inverse cipher

        function byte unsigned xtime(byte unsigned x);

        // Multiplication by 2 over GF(256)

        // Refer to FIPS-197 spec section 4.2.1 on definition of GF(256) multiplication

                xtime = (x[7])? (x<<1) ^ 8'h1b : x<<1;

        endfunction

        function byte unsigned GFmul3(byte unsigned x);

        // Multiply by 3 over GF(256)

        // 3*x = 2*x +x

                GFmul3 = xtime(x) ^ x;

        endfunction

        function byte unsigned GFmul4(byte unsigned x);

        // Multiply by 4 over GF(256)

        // 4*x = 2*(2*x)

                GFmul4 = xtime(xtime(x));

        endfunction

        function byte unsigned GFmul8(byte unsigned x);

        // Multiply by 8 over GF(256)

        // 8*x = 2*(4*x)

                GFmul8 = xtime(GFmul4(x));

        endfunction

        function byte unsigned GFmul9(byte unsigned x);

        // Multiply by 9 over GF(256)

        // 9*x = 8*x + x

        // Addition over GF(256) is xor

                GFmul9 = GFmul8(x) ^ x;

        endfunction

        function byte unsigned GFmulb(byte unsigned x);

        // Multiply by 0xb over GF(256)

        // b*x = 8*x + 2*x +x

                GFmulb = GFmul8(x) ^ xtime(x) ^ x;

        endfunction

        function byte unsigned GFmuld(byte unsigned x);

        // Multiply by 0xd over GF(256)

        // d*x = 8*x + 4*x + x

                GFmuld = GFmul8(x) ^ GFmul4(x) ^ x;

        endfunction

        function byte unsigned GFmule(byte unsigned x);

        // Multiply by 0xe over GF(256)

        // e*x = 8*x + 4*x +2*x

                GFmule = GFmul8(x) ^ GFmul4(x) ^ xtime(x);

        endfunction

        assign x2 = xtime(d);

        assign x3 = GFmul3(d);

        assign x9 = GFmul9(d);

        assign xb = GFmulb(d);

        assign xd = GFmuld(d);

        assign xe = GFmule(d);

endmodule