//======================================================================
//
// aes_decipher_block.v
// --------------------
// The AES decipher round. A pure combinational module that implements
// the initial round, main round and final round logic for
// decciper operations.
//
//
// Author: Joachim Strombergson
// Copyright (c) 2014, NORDUnet A/S
// 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 NORDUnet 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 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//======================================================================
module aes_decipher_block(
input wire clk,
input wire reset_n,
input wire next,
input wire keylen,
output wire [3 : 0] round,
input wire [127 : 0] round_key,
input wire [127 : 0] block,
output wire [127 : 0] new_block,
output wire ready
);
//----------------------------------------------------------------
// Internal constant and parameter definitions.
//----------------------------------------------------------------
localparam AES_128_BIT_KEY = 1'h0;
localparam AES_256_BIT_KEY = 1'h1;
localparam AES128_ROUNDS = 4'ha;
localparam AES256_ROUNDS = 4'he;
localparam NO_UPDATE = 3'h0;
localparam INIT_UPDATE = 3'h1;
localparam SBOX_UPDATE = 3'h2;
localparam MAIN_UPDATE = 3'h3;
localparam FINAL_UPDATE = 3'h4;
localparam CTRL_IDLE = 3'h0;
localparam CTRL_INIT = 3'h1;
localparam CTRL_MAIN = 3'h2;
localparam CTRL_FINAL = 3'h3;
//----------------------------------------------------------------
// Gaolis multiplication functions for Inverse MixColumn.
//----------------------------------------------------------------
function [7 : 0] gm2(input [7 : 0] op);
begin
gm2 = {op[6 : 0], 1'b0} ^ (8'h1b & {8{op[7]}});
end
endfunction // gm2
function [7 : 0] gm3(input [7 : 0] op);
begin
gm3 = gm2(op) ^ op;
end
endfunction // gm3
function [7 : 0] gm4(input [7 : 0] op);
begin
gm4 = gm2(gm2(op));
end
endfunction // gm4
function [7 : 0] gm8(input [7 : 0] op);
begin
gm8 = gm2(gm4(op));
end
endfunction // gm8
function [7 : 0] gm09(input [7 : 0] op);
begin
gm09 = gm8(op) ^ op;
end
endfunction // gm09
function [7 : 0] gm11(input [7 : 0] op);
begin
gm11 = gm8(op) ^ gm2(op) ^ op;
end
endfunction // gm11
function [7 : 0] gm13(input [7 : 0] op);
begin
gm13 = gm8(op) ^ gm4(op) ^ op;
end
endfunction // gm13
function [7 : 0] gm14(input [7 : 0] op);
begin
gm14 = gm8(op) ^ gm4(op) ^ gm2(op);
end
endfunction // gm14
function [31 : 0] inv_mixw(input [31 : 0] w);
reg [7 : 0] b0, b1, b2, b3;
reg [7 : 0] mb0, mb1, mb2, mb3;
begin
b0 = w[31 : 24];
b1 = w[23 : 16];
b2 = w[15 : 08];
b3 = w[07 : 00];
mb0 = gm14(b0) ^ gm11(b1) ^ gm13(b2) ^ gm09(b3);
mb1 = gm09(b0) ^ gm14(b1) ^ gm11(b2) ^ gm13(b3);
mb2 = gm13(b0) ^ gm09(b1) ^ gm14(b2) ^ gm11(b3);
mb3 = gm11(b0) ^ gm13(b1) ^ gm09(b2) ^ gm14(b3);
inv_mixw = {mb0, mb1, mb2, mb3};
end
endfunction // mixw
function [127 : 0] inv_mixcolumns(input [127 : 0] data);
reg [31 : 0] w0, w1, w2, w3;
reg [31 : 0] ws0, ws1, ws2, ws3;
begin
w0 = data[127 : 096];
w1 = data[095 : 064];
w2 = data[063 : 032];
w3 = data[031 : 000];
ws0 = inv_mixw(w0);
ws1 = inv_mixw(w1);
ws2 = inv_mixw(w2);
ws3 = inv_mixw(w3);
inv_mixcolumns = {ws0, ws1, ws2, ws3};
end
endfunction // inv_mixcolumns
function [127 : 0] inv_shiftrows(input [127 : 0] data);
reg [31 : 0] w0, w1, w2, w3;
reg [31 : 0] ws0, ws1, ws2, ws3;
begin
w0 = data[127 : 096];
w1 = data[095 : 064];
w2 = data[063 : 032];
w3 = data[031 : 000];
ws0 = {w0[31 : 24], w3[23 : 16], w2[15 : 08], w1[07 : 00]};
ws1 = {w1[31 : 24], w0[23 : 16], w3[15 : 08], w2[07 : 00]};
ws2 = {w2[31 : 24], w1[23 : 16], w0[15 : 08], w3[07 : 00]};
ws3 = {w3[31 : 24], w2[23 : 16], w1[15 : 08], w0[07 : 00]};
inv_shiftrows = {ws0, ws1, ws2, ws3};
end
endfunction // inv_shiftrows
function [127 : 0] addroundkey(input [127 : 0] data, input [127 : 0] rkey);
begin
addroundkey = data ^ rkey;
end
endfunction // addroundkey
//----------------------------------------------------------------
// Registers including update variables and write enable.
//----------------------------------------------------------------
reg [127 : 0] block_reg;
reg [127 : 0] block_new;
reg block_we;
reg [3 : 0] round_ctr_reg;
reg [3 : 0] round_ctr_new;
reg round_ctr_we;
reg round_ctr_set;
reg round_ctr_dec;
reg ready_reg;
reg ready_new;
reg ready_we;
reg [2 : 0] dec_ctrl_reg;
reg [2 : 0] dec_ctrl_new;
reg dec_ctrl_we;
//----------------------------------------------------------------
// Wires.
//----------------------------------------------------------------
reg [31 : 0] sboxw0;
reg [31 : 0] sboxw1;
reg [31 : 0] sboxw2;
reg [31 : 0] sboxw3;
wire [31 : 0] new_sboxw0;
wire [31 : 0] new_sboxw1;
wire [31 : 0] new_sboxw2;
wire [31 : 0] new_sboxw3;
reg [2 : 0] update_type;
//----------------------------------------------------------------
// Inverse S-boxes.
//----------------------------------------------------------------
aes_inv_sbox inv_sbox_inst0(.sword(sboxw0), .new_sword(new_sboxw0));
aes_inv_sbox inv_sbox_inst1(.sword(sboxw1), .new_sword(new_sboxw1));
aes_inv_sbox inv_sbox_inst2(.sword(sboxw2), .new_sword(new_sboxw2));
aes_inv_sbox inv_sbox_inst3(.sword(sboxw3), .new_sword(new_sboxw3));
//----------------------------------------------------------------
// Concurrent connectivity for ports etc.
//----------------------------------------------------------------
assign new_block = block_reg;
assign round = round_ctr_reg;
assign ready = ready_reg;
//----------------------------------------------------------------
// reg_update
//
// Update functionality for all registers in the core.
// All registers are positive edge triggered with synchronous
// active low reset. All registers have write enable.
//----------------------------------------------------------------
always @ (posedge clk or negedge reset_n)
begin: reg_update
if (!reset_n)
begin
block_reg <= 128'h0;
round_ctr_reg <= 4'h0;
ready_reg <= 1'b1;
dec_ctrl_reg <= CTRL_IDLE;
end
else
begin
if (block_we)
block_reg <= block_new;
if (round_ctr_we)
round_ctr_reg <= round_ctr_new;
if (ready_we)
ready_reg <= ready_new;
if (dec_ctrl_we)
dec_ctrl_reg <= dec_ctrl_new;
end
end // reg_update
//----------------------------------------------------------------
// round_logic
//
// The logic needed to implement init, main and final rounds.
//----------------------------------------------------------------
always @*
begin : round_logic
reg [127 : 0] subbytes_block, inv_shiftrows_block, inv_mixcolumns_block;
reg [127 : 0] addkey_block;
inv_shiftrows_block = 128'h0;
inv_mixcolumns_block = 128'h0;
addkey_block = 128'h0;
block_new = 128'h0;
block_we = 1'b0;
sboxw0 = block_reg[127 : 96];
sboxw1 = block_reg[95 : 64];
sboxw2 = block_reg[63 : 32];
sboxw3 = block_reg[31 : 0];
subbytes_block = {new_sboxw0, new_sboxw1, new_sboxw2, new_sboxw3};
case (update_type)
INIT_UPDATE:
begin
addkey_block = addroundkey(block, round_key);
inv_shiftrows_block = inv_shiftrows(addkey_block);
block_new = inv_shiftrows_block;
block_we = 1'b1;
end
MAIN_UPDATE:
begin
addkey_block = addroundkey(subbytes_block, round_key);
inv_mixcolumns_block = inv_mixcolumns(addkey_block);
inv_shiftrows_block = inv_shiftrows(inv_mixcolumns_block);
block_new = inv_shiftrows_block;
block_we = 1'b1;
end
FINAL_UPDATE:
begin
block_new = addroundkey(subbytes_block, round_key);
block_we = 1'b1;
end
default:
begin
end
endcase // case (update_type)
end // round_logic
//----------------------------------------------------------------
// round_ctr
//
// The round counter with reset and increase logic.
//----------------------------------------------------------------
always @*
begin : round_ctr
round_ctr_new = 4'h0;
round_ctr_we = 1'b0;
if (round_ctr_set)
begin
if (keylen == AES_256_BIT_KEY)
begin
round_ctr_new = AES256_ROUNDS;
end
else
begin
round_ctr_new = AES128_ROUNDS;
end
round_ctr_we = 1'b1;
end
else if (round_ctr_dec)
begin
round_ctr_new = round_ctr_reg - 1'b1;
round_ctr_we = 1'b1;
end
end // round_ctr
//----------------------------------------------------------------
// decipher_ctrl
//
// The FSM that controls the decipher operations.
//----------------------------------------------------------------
always @*
begin: decipher_ctrl
round_ctr_dec = 1'b0;
round_ctr_set = 1'b0;
ready_new = 1'b0;
ready_we = 1'b0;
update_type = NO_UPDATE;
dec_ctrl_new = CTRL_IDLE;
dec_ctrl_we = 1'b0;
case(dec_ctrl_reg)
CTRL_IDLE:
begin
if (next)
begin
round_ctr_set = 1'b1;
ready_new = 1'b0;
ready_we = 1'b1;
dec_ctrl_new = CTRL_INIT;
dec_ctrl_we = 1'b1;
end
end
CTRL_INIT:
begin
round_ctr_dec = 1'b1;
update_type = INIT_UPDATE;
dec_ctrl_new = CTRL_MAIN;
dec_ctrl_we = 1'b1;
end
CTRL_MAIN:
begin
if (round_ctr_reg > 0)
begin
round_ctr_dec = 1'b1;
update_type = MAIN_UPDATE;
end
else
begin
update_type = FINAL_UPDATE;
ready_new = 1'b1;
ready_we = 1'b1;
dec_ctrl_new = CTRL_IDLE;
dec_ctrl_we = 1'b1;
end
end
default:
begin
// Empty. Just here to make the synthesis tool happy.
end
endcase // case (dec_ctrl_reg)
end // decipher_ctrl
endmodule // aes_decipher_block
//======================================================================
// EOF aes_decipher_block.v
//======================================================================
