path: root/src/rtl/aes_key_mem.v

//======================================================================
//
// aes_key_mem.v
// -------------
// The AES key memort including round key generator.
//
//
// 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_key_mem(
                   input wire            clk,
                   input wire            reset_n,

                   input wire [255 : 0]  key,
                   input wire            keylen,
                   input wire            init,

                   input wire    [3 : 0] round,
                   output wire [127 : 0] round_key,
                   output wire           ready
                  );


  //----------------------------------------------------------------
  // Parameters.
  //----------------------------------------------------------------
  localparam AES_128_BIT_KEY = 1'h0;
  localparam AES_256_BIT_KEY = 1'h1;

  localparam AES_128_NUM_ROUNDS = 4'ha;
  localparam AES_256_NUM_ROUNDS = 4'he;

  localparam CTRL_IDLE     = 3'h0;
  localparam CTRL_INIT     = 3'h1;
  localparam CTRL_GENERATE = 3'h2;
  localparam CTRL_DONE     = 3'h3;


  //----------------------------------------------------------------
  // Registers.
  //----------------------------------------------------------------
  reg [127 : 0] key_mem [0 : 14];
  reg [127 : 0] key_mem_new;
  reg           key_mem_we;

  reg [127 : 0] prev_key0_reg;
  reg [127 : 0] prev_key0_new;
  reg           prev_key0_we;

  reg [127 : 0] prev_key1_reg;
  reg [127 : 0] prev_key1_new;
  reg           prev_key1_we;

  reg [3 : 0] round_ctr_reg;
  reg [3 : 0] round_ctr_new;
  reg         round_ctr_rst;
  reg         round_ctr_inc;
  reg         round_ctr_we;

  reg [2 : 0] key_mem_ctrl_reg;
  reg [2 : 0] key_mem_ctrl_new;
  reg         key_mem_ctrl_we;

  reg         ready_reg;
  reg         ready_new;
  reg         ready_we;

  reg [7 : 0] rcon_reg;
  reg [7 : 0] rcon_new;
  reg         rcon_we;
  reg         rcon_set;
  reg         rcon_next;


  //----------------------------------------------------------------
  // Wires.
  //----------------------------------------------------------------
  reg [31 : 0]  sboxw;
  wire [31 : 0] new_sboxw;

  reg           round_key_update;
  reg [3 : 0]   num_rounds;

  reg [127 : 0] tmp_round_key;


  //----------------------------------------------------------------
  // Concurrent assignments for ports.
  //----------------------------------------------------------------
  assign round_key  = tmp_round_key;
  assign ready      = ready_reg;


  //----------------------------------------------------------------
  // S-box for key expansion.
  //----------------------------------------------------------------
  aes_sbox sbox_inst(.sboxw(sboxw), .new_sboxw(new_sboxw));


  //----------------------------------------------------------------
  // reg_update
  //
  // Update functionality for all registers in the core.
  // All registers are positive edge triggered with asynchronous
  // active low reset. All registers have write enable.
  //----------------------------------------------------------------
  always @ (posedge clk or negedge reset_n)
    begin: reg_update
      integer i;

      if (!reset_n)
        begin
          for (i = 0 ; i < 4 ; i = i + 1)
            key_mem [i] <= 128'h0;

          rcon_reg         <= 8'h0;
          ready_reg        <= 1'b0;
          round_ctr_reg    <= 4'h0;
          key_mem_ctrl_reg <= CTRL_IDLE;
        end
      else
        begin
          if (round_ctr_we)
            round_ctr_reg <= round_ctr_new;

          if (ready_we)
            ready_reg <= ready_new;

          if (rcon_we)
            rcon_reg <= rcon_new;

          if (key_mem_we)
            key_mem[round_ctr_reg] <= key_mem_new;

          if (prev_key0_we)
            prev_key0_reg <= prev_key0_new;

          if (prev_key1_we)
            prev_key1_reg <= prev_key1_new;

          if (key_mem_ctrl_we)
            key_mem_ctrl_reg <= key_mem_ctrl_new;
        end
    end // reg_update


  //----------------------------------------------------------------
  // key_mem_read
  //
  // Combinational read port for the key memory.
  //----------------------------------------------------------------
  always @*
    begin : key_mem_read
      tmp_round_key = key_mem[round];
    end // key_mem_read


  //----------------------------------------------------------------
  // round_key_gen
  //
  // The round key generator logic for AES-128 and AES-256.
  //----------------------------------------------------------------
  always @*
    begin: round_key_gen
      reg [31 : 0] w0, w1, w2, w3, w4, w5, w6, w7;
      reg [31 : 0] k0, k1, k2, k3;
      reg [31 : 0] rconw, rotstw, tw, trw;

      // Default assignments.
      key_mem_new   = 128'h0;
      key_mem_we    = 1'b0;
      prev_key0_new = 128'h0;
      prev_key0_we  = 1'b0;
      prev_key1_new = 128'h0;
      prev_key1_we  = 1'b0;

      k0 = 32'h0;
      k1 = 32'h0;
      k2 = 32'h0;
      k3 = 32'h0;

      rcon_set   = 1'b1;
      rcon_next  = 1'b0;

      // Extract words and calculate intermediate values.
      // Perform rotation of sbox word etc.
      w0 = prev_key0_reg[127 : 096];
      w1 = prev_key0_reg[095 : 064];
      w2 = prev_key0_reg[063 : 032];
      w3 = prev_key0_reg[031 : 000];

      w4 = prev_key1_reg[127 : 096];
      w5 = prev_key1_reg[095 : 064];
      w6 = prev_key1_reg[063 : 032];
      w7 = prev_key1_reg[031 : 000];

      rconw = {rcon_reg, 24'h0};
      sboxw = w7;
      rotstw = {new_sboxw[23 : 00], new_sboxw[31 : 24]};
      trw = rotstw ^ rconw;
      tw = new_sboxw;

      // Generate the specific round keys.
      if (round_key_update)
        begin
          rcon_set   = 1'b0;
          key_mem_we = 1'b1;
          case (keylen)
            AES_128_BIT_KEY:
              begin
                if (round_ctr_reg == 0)
                  begin
                    key_mem_new   = key[255 : 128];
                    prev_key1_new = key[255 : 128];
                    prev_key1_we  = 1'b1;
                    rcon_next     = 1'b1;
                  end
                else
                  begin
                    k0 = w4 ^ trw;
                    k1 = w5 ^ w4 ^ trw;
                    k2 = w6 ^ w5 ^ w4 ^ trw;
                    k3 = w7 ^ w6 ^ w5 ^ w4 ^ trw;

                    key_mem_new   = {k0, k1, k2, k3};
                    prev_key1_new = {k0, k1, k2, k3};
                    prev_key1_we  = 1'b1;
                    rcon_next     = 1'b1;
                  end
              end

            AES_256_BIT_KEY:
              begin
                if (round_ctr_reg == 0)
                  begin
                    key_mem_new   = key[255 : 128];
                    prev_key0_new = key[255 : 128];
                    prev_key0_we  = 1'b1;
                  end
                else if (round_ctr_reg == 1)
                  begin
                    key_mem_new   = key[127 : 0];
                    prev_key1_new = key[127 : 0];
                    prev_key1_we  = 1'b1;
                    rcon_next     = 1'b1;
                  end
                else
                  begin
                    if (round_ctr_reg[0] == 0)
                      begin
                        k0 = w0 ^ trw;
                        k1 = w1 ^ w0 ^ trw;
                        k2 = w2 ^ w1 ^ w0 ^ trw;
                        k3 = w3 ^ w2 ^ w1 ^ w0 ^ trw;
                      end
                    else
                      begin
                        k0 = w0 ^ tw;
                        k1 = w1 ^ w0 ^ tw;
                        k2 = w2 ^ w1 ^ w0 ^ tw;
                        k3 = w3 ^ w2 ^ w1 ^ w0 ^ tw;
                        rcon_next = 1'b1;
                      end

                    // Store the generated round keys.
                    key_mem_new   = {k0, k1, k2, k3};
                    prev_key1_new = {k0, k1, k2, k3};
                    prev_key1_we  = 1'b1;
                    prev_key0_new = prev_key1_reg;
                    prev_key0_we  = 1'b1;
                  end
              end

            default:
              begin
              end
          endcase // case (keylen)
        end
    end // round_key_gen


  //----------------------------------------------------------------
  // rcon_logic
  //
  // Caclulates the rcon value for the different key expansion
  // iterations.
  //----------------------------------------------------------------
  always @*
    begin : rcon_logic
      reg [7 : 0] tmp_rcon;
      rcon_new = 8'h00;
      rcon_we  = 1'b0;

      tmp_rcon = {rcon_reg[6 : 0], 1'b0} ^ (8'h1b & {8{rcon_reg[7]}});

      if (rcon_set)
        begin
          rcon_new = 8'h8d;
          rcon_we  = 1'b1;
        end

      if (rcon_next)
        begin
          rcon_new = tmp_rcon[7 : 0];
          rcon_we  = 1'b1;
        end
    end


  //----------------------------------------------------------------
  // round_ctr
  //
  // The round counter logic with increase and reset.
  //----------------------------------------------------------------
  always @*
    begin : round_ctr
      round_ctr_new = 4'h0;
      round_ctr_we  = 1'b0;

      if (round_ctr_rst)
        begin
          round_ctr_new = 4'h0;
          round_ctr_we  = 1'b1;
        end

      else if (round_ctr_inc)
        begin
          round_ctr_new = round_ctr_reg + 1'b1;
          round_ctr_we  = 1'b1;
        end
    end


  //----------------------------------------------------------------
  // num_rounds_logic
  //
  // Logic to select the number of rounds to generate keys for
  //----------------------------------------------------------------
  always @*
    begin : num_rounds_logic
      num_rounds = 4'h0;

      case (keylen)
        AES_128_BIT_KEY:
          begin
            num_rounds = AES_128_NUM_ROUNDS;
          end

        AES_256_BIT_KEY:
          begin
            num_rounds = AES_256_NUM_ROUNDS;
          end

        default:
          begin
          end
      endcase // case (keylen)
    end


  //----------------------------------------------------------------
  // key_mem_ctrl
  //
  //
  // The FSM that controls the round key generation.
  //----------------------------------------------------------------
  always @*
    begin: key_mem_ctrl
      // Default assignments.
      ready_new        = 1'b0;
      ready_we         = 1'b0;
      round_key_update = 1'b0;
      round_ctr_rst    = 1'b0;
      round_ctr_inc    = 1'b0;
      key_mem_ctrl_new = CTRL_IDLE;
      key_mem_ctrl_we  = 1'b0;

      case(key_mem_ctrl_reg)
        CTRL_IDLE:
          begin
            if (init)
              begin
                ready_new        = 1'b0;
                ready_we         = 1'b1;
                key_mem_ctrl_new = CTRL_INIT;
                key_mem_ctrl_we  = 1'b1;
              end
          end

        CTRL_INIT:
          begin
            round_ctr_rst    = 1'b1;
            key_mem_ctrl_new = CTRL_GENERATE;
            key_mem_ctrl_we  = 1'b1;
          end

        CTRL_GENERATE:
          begin
            round_ctr_inc    = 1'b1;
            round_key_update = 1'b1;
            if (round_ctr_reg == num_rounds)
              begin
                key_mem_ctrl_new = CTRL_DONE;
                key_mem_ctrl_we  = 1'b1;
              end
          end

        CTRL_DONE:
          begin
            ready_new        = 1'b1;
            ready_we         = 1'b1;
            key_mem_ctrl_new = CTRL_IDLE;
            key_mem_ctrl_we  = 1'b1;
          end

        default:
          begin
          end
      endcase // case (key_mem_ctrl_reg)

    end // key_mem_ctrl
endmodule // aes_key_mem

//======================================================================
// EOF aes_key_mem.v
//======================================================================