Subversion Repositories aes_decrypt_fpga

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

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

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

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//// 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                                           ////

////                                                                                                                            //// ///

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//// This module computes one column of the InvMixColumns() defined     ////

//// in section 5.3.3 in FIPS-197 specification.                                        ////

////                                                                                                                            ////

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

module InvMixCol_slice(

        input   [7:0]   S0c,

        input   [7:0]   S1c,

        input   [7:0]   S2c,

        input   [7:0]   S3c,

        input   bypass,

        output  [31:0]  new_S);

        wire    [7:0]   S0cx9, S0cxb, S0cxd, S0cxe;

        wire    [7:0]   S1cx9, S1cxb, S1cxd, S1cxe;

        wire    [7:0]   S2cx9, S2cxb, S2cxd, S2cxe;

        wire    [7:0]   S3cx9, S3cxb, S3cxd, S3cxe;

        wire    [7:0]   sum0, sum1, sum2, sum3;

        // GF multipliers to generate products for x9, xb, xd, xe

        gfmul_inv gfmul_inv_u0(.d(S0c), .x2(), .x3(), .x9(S0cx9), .xb(S0cxb), .xd(S0cxd), .xe(S0cxe));

        gfmul_inv gfmul_inv_u1(.d(S1c), .x2(), .x3(), .x9(S1cx9), .xb(S1cxb), .xd(S1cxd), .xe(S1cxe));

        gfmul_inv gfmul_inv_u2(.d(S2c), .x2(), .x3(), .x9(S2cx9), .xb(S2cxb), .xd(S2cxd), .xe(S2cxe));

        gfmul_inv gfmul_inv_u3(.d(S3c), .x2(), .x3(), .x9(S3cx9), .xb(S3cxb), .xd(S3cxd), .xe(S3cxe));

        // Compute InvMixColumns according to section 5.3.3 of FIPS-197 spec.

        // Feed input through directly when bypass=1.

        assign sum0 = bypass ? S0c : S0cxe ^ S1cxb ^ S2cxd ^ S3cx9;

        assign sum1 = bypass ? S1c : S0cx9 ^ S1cxe ^ S2cxb ^ S3cxd;

        assign sum2 = bypass ? S2c : S0cxd ^ S1cx9 ^ S2cxe ^ S3cxb;

        assign sum3 = bypass ? S3c : S0cxb ^ S1cxd ^ S2cx9 ^ S3cxe;

        assign new_S = {sum0, sum1, sum2, sum3};

endmodule