// ======================================================================
// DES encryption/decryption
// algorithm according:FIPS 46-3 specification
// Copyright (C) 2012 Torsten Meissner
//-----------------------------------------------------------------------
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// This program 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write:the Free Software
// Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
// ======================================================================


`timescale 1ns/1ps


module des
  (
    input             reset_i,  // async reset
    input             clk_i,    // clock
    input             mode_i,   // des-mode: 0 = encrypt, 1 = decrypt
    input      [0:63] key_i,    // key input
    input      [0:63] data_i,   // data input
    input             valid_i,  // input key/data valid flag
    output reg [0:63] data_o,   // data output
    output            valid_o   // output data valid flag
  );


`include "../../rtl/verilog/des_pkg.v"

  // valid, mode register
  reg [0:18] valid;
  reg [0:17] mode;

  // algorithm pipeline register
  // key calculation register
  reg [0:27] c0;
  reg [0:27] c1;
  reg [0:27] c2;
  reg [0:27] c3;
  reg [0:27] c4;
  reg [0:27] c5;
  reg [0:27] c6;
  reg [0:27] c7;
  reg [0:27] c8;
  reg [0:27] c9;
  reg [0:27] c10;
  reg [0:27] c11;
  reg [0:27] c12;
  reg [0:27] c13;
  reg [0:27] c14;
  reg [0:27] c15;
  reg [0:27] c16;
  reg [0:27] d0;
  reg [0:27] d1;
  reg [0:27] d2;
  reg [0:27] d3;
  reg [0:27] d4;
  reg [0:27] d5;
  reg [0:27] d6;
  reg [0:27] d7;
  reg [0:27] d8;
  reg [0:27] d9;
  reg [0:27] d10;
  reg [0:27] d11;
  reg [0:27] d12;
  reg [0:27] d13;
  reg [0:27] d14;
  reg [0:27] d15;
  reg [0:27] d16;
  // key register
  wire [0:47] key1;
  wire [0:47] key2;
  wire [0:47] key3;
  wire [0:47] key4;
  wire [0:47] key5;
  wire [0:47] key6;
  wire [0:47] key7;
  wire [0:47] key8;
  wire [0:47] key9;
  wire [0:47] key10;
  wire [0:47] key11;
  wire [0:47] key12;
  wire [0:47] key13;
  wire [0:47] key14;
  wire [0:47] key15;
  wire [0:47] key16;
  // register for left, right data blocks
  reg [0:31] l;
  reg [0:31] l0;
  reg [0:31] l1;
  reg [0:31] l2;
  reg [0:31] l3;
  reg [0:31] l4;
  reg [0:31] l5;
  reg [0:31] l6;
  reg [0:31] l7;
  reg [0:31] l8;
  reg [0:31] l9;
  reg [0:31] l10;
  reg [0:31] l11;
  reg [0:31] l12;
  reg [0:31] l13;
  reg [0:31] l14;
  reg [0:31] l15;
  reg [0:31] l16;
  reg [0:31] r;
  reg [0:31] r0;
  reg [0:31] r1;
  reg [0:31] r2;
  reg [0:31] r3;
  reg [0:31] r4;
  reg [0:31] r5;
  reg [0:31] r6;
  reg [0:31] r7;
  reg [0:31] r8;
  reg [0:31] r9;
  reg [0:31] r10;
  reg [0:31] r11;
  reg [0:31] r12;
  reg [0:31] r13;
  reg [0:31] r14;
  reg [0:31] r15;
  reg [0:31] r16;

  wire valid_o = valid[18];

  // valid, mode register
  always @(posedge clk_i, negedge reset_i) begin
    if(~reset_i) begin
      valid <= 0;
      mode  <= 0;
    end
    else begin
      // shift registers
      valid[1:18] <= valid[0:17];
      valid[0]    <= valid_i;
      mode[1:17]  <= mode[0:16];
      mode[0]     <= mode_i;
    end
  end

  // des algorithm pipeline
  always @(posedge clk_i, negedge reset_i) begin
    if(~reset_i) begin
      l      <= 0;
      r      <= 0;
      l0     <= 0;
      l1     <= 0;
      l2     <= 0;
      l3     <= 0;
      l4     <= 0;
      l5     <= 0;
      l6     <= 0;
      l7     <= 0;
      l8     <= 0;
      l9     <= 0;
      l10    <= 0;
      l11    <= 0;
      l12    <= 0;
      l13    <= 0;
      l14    <= 0;
      l15    <= 0;
      l16    <= 0;
      r0     <= 0;
      r1     <= 0;
      r2     <= 0;
      r3     <= 0;
      r4     <= 0;
      r5     <= 0;
      r6     <= 0;
      r7     <= 0;
      r8     <= 0;
      r9     <= 0;
      r10    <= 0;
      r11    <= 0;
      r12    <= 0;
      r13    <= 0;
      r14    <= 0;
      r15    <= 0;
      r16    <= 0;
      data_o <= 0;
    end
    else begin
      // output stage
      data_o <= ipn({r16, l16});
      // 16. stage
      l16   <= r15;
      r16   <= l15 ^ (f(r15, key16));
      // 15. stage
      l15   <= r14;
      r15   <= l14 ^ (f(r14, key15));
      // 14. stage
      l14   <= r13;
      r14   <= l13 ^ (f(r13, key14));
      // 13. stage
      l13   <= r12;
      r13   <= l12 ^ (f(r12, key13));
      // 12. stage
      l12   <= r11;
      r12   <= l11 ^ (f(r11, key12));
      // 11. stage
      l11   <= r10;
      r11   <= l10 ^ (f(r10, key11));
      // 10. stage
      l10   <= r9;
      r10   <= l9 ^ (f(r9, key10));
      // 9. stage
      l9   <= r8;
      r9   <= l8 ^ (f(r8, key9));
      // 8. stage
      l8   <= r7;
      r8   <= l7 ^ (f(r7, key8));
      // 7. stage
      l7   <= r6;
      r7   <= l6 ^ (f(r6, key7));
      // 6. stage
      l6   <= r5;
      r6   <= l5 ^ (f(r5, key6));
      // 5. stage
      l5   <= r4;
      r5   <= l4 ^ (f(r4, key5));
      // 4. stage
      l4   <= r3;
      r4   <= l3 ^ (f(r3, key4));
      // 3. stage
      l3   <= r2;
      r3   <= l2 ^ (f(r2, key3));
      // 2. stage
      l2   <= r1;
      r2   <= l1 ^ (f(r1, key2));
      // 1. stage
      l1   <= r0;
      r1   <= l0 ^ (f(r0, key1));
      // 1. state
      l0   <= l;
      r0   <= r;
      // input stage
      l   <= ip0(data_i);
      r   <= ip1(data_i);
    end
  end

  // des key pipeline
  always @(posedge clk_i, negedge reset_i) begin
    if(~reset_i) begin
      c0     <= 0;
      c1     <= 0;
      c2     <= 0;
      c3     <= 0;
      c4     <= 0;
      c5     <= 0;
      c6     <= 0;
      c7     <= 0;
      c8     <= 0;
      c9     <= 0;
      c10    <= 0;
      c11    <= 0;
      c12    <= 0;
      c13    <= 0;
      c14    <= 0;
      c15    <= 0;
      c16    <= 0;
      d0     <= 0;
      d1     <= 0;
      d2     <= 0;
      d3     <= 0;
      d4     <= 0;
      d5     <= 0;
      d6     <= 0;
      d7     <= 0;
      d8     <= 0;
      d9     <= 0;
      d10    <= 0;
      d11    <= 0;
      d12    <= 0;
      d13    <= 0;
      d14    <= 0;
      d15    <= 0;
      d16    <= 0;
    end
    else begin
      // input stage
      c0 <= pc1_c(key_i);
      d0 <= pc1_d(key_i);
      // 1st stage
      if (~mode[0]) begin
        c1 <= {c0[1:27], c0[0]};
        d1 <= {c0[1:27], c0[0]};
      end
      else begin
        c1 <= c0;
        d1 <= d0;
      end
      // 2nd stage
      if (~mode[1]) begin
        c2 <= {c1[1:27], c1[0]};
        d2 <= {d1[1:27], d1[0]};
      end
      else begin
        c2 <= {c1[27], c1[0:26]};
        d2 <= {d1[27], d1[0:26]};
      end
      // 3rd stage
      if (~mode[2]) begin
        c3 <= {c2[2:27], c2[0:1]};
        d3 <= {d2[2:27], d2[0:1]};
      end
      else begin
        c3 <= {c2[26:27], c2[0:25]};
        d3 <= {d2[26:27], d2[0:25]};
      end
      // 4th stage
      if (~mode[3]) begin
        c4 <= {c3[2:27], c3[0:1]};
        d4 <= {d3[2:27], d3[0:1]};
      end
      else begin
        c4 <= {c3[26:27], c3[0:25]};
        d4 <= {d3[26:27], d3[0:25]};
      end
      // 5th stage
      if (~mode[4]) begin
        c5 <= {c4[2:27], c4[0:1]};
        d5 <= {d4[2:27], d4[0:1]};
      end
      else begin
        c5 <= {c4[26:27], c4[0:25]};
        d5 <= {d4[26:27], d4[0:25]};
      end
      // 6. stage
      if (~mode[5]) begin
        c6 <= {c5[2:27], c5[0:1]};
        d6 <= {d5[2:27], d5[0:1]};
      end
      else begin
        c6 <= {c5[26:27], c5[0:25]};
        d6 <= {d5[26:27], d5[0:25]};
      end
      // 7. stage
      if (~mode[6]) begin
        c7 <= {c6[2:27], c6[0:1]};
        d7 <= {d6[2:27], d6[0:1]};
      end
      else begin
        c7 <= {c6[26:27], c6[0:25]};
        d7 <= {d6[26:27], d6[0:25]};
      end
      // 8. stage
      if (~mode[7]) begin
        c8 <= {c7[2:27], c7[0:1]};
        d8 <= {d7[2:27], d7[0:1]};
      end
      else begin
        c8 <= {c7[26:27], c7[0:25]};
        d8 <= {d7[26:27], d7[0:25]};
      end
      // 9. stage
      if (~mode[8]) begin
        c9 <= {c8[2:27], c8[0:1]};
        d9 <= {d8[2:27], d8[0:1]};
      end
      else begin
        c9 <= {c8[26:27], c8[0:25]};
        d9 <= {d8[26:27], d8[0:25]};
      end
      // 10. stage
      if (~mode[9]) begin
        c10 <= {c9[2:27], c9[0:1]};
        d10 <= {d9[2:27], d9[0:1]};
      end
      else begin
        c10 <= {c9[26:27], c9[0:25]};
        d10 <= {d9[26:27], d9[0:25]};
      end
      // 6. stage
      if (~mode[10]) begin
        c11 <= {c10[2:27], c10[0:1]};
        d11 <= {d10[2:27], d10[0:1]};
      end
      else begin
        c11 <= {c10[26:27], c10[0:25]};
        d11 <= {d10[26:27], d10[0:25]};
      end
      // 6. stage
      if (~mode[11]) begin
        c12 <= {c11[2:27], c11[0:1]};
        d12 <= {d11[2:27], d11[0:1]};
      end
      else begin
        c12 <= {c11[26:27], c11[0:25]};
        d12 <= {d11[26:27], d11[0:25]};
      end
      // 6. stage
      if (~mode[12]) begin
        c13 <= {c12[2:27], c12[0:1]};
        d13 <= {d12[2:27], d12[0:1]};
      end
      else begin
        c13 <= {c12[26:27], c12[0:25]};
        d13 <= {d12[26:27], d12[0:25]};
      end
      // 6. stage
      if (~mode[13]) begin
        c14 <= {c13[2:27], c13[0:1]};
        d14 <= {d13[2:27], d13[0:1]};
      end
      else begin
        c14 <= {c13[26:27], c13[0:25]};
        d14 <= {d13[26:27], d13[0:25]};
      end
      // 6. stage
      if (~mode[14]) begin
        c15 <= {c14[2:27], c14[0:1]};
        d15 <= {d14[2:27], d14[0:1]};
      end
      else begin
        c15 <= {c14[26:27], c14[0:25]};
        d15 <= {d14[26:27], d14[0:25]};
      end
      // 6. stage
      if (~mode[15]) begin
        c16 <= {c15[1:27], c15[0]};
        d16 <= {d15[1:27], d15[0]};
      end
      else begin
        c16 <= {c15[27], c15[0:26]};
        d16 <= {d15[27], d15[0:26]};
      end
    end
  end

  // key assignments
  assign key1 = pc2({c1, d1});
  assign key2 = pc2({c2, d2});
  assign key3 = pc2({c3, d3});
  assign key4 = pc2({c4, d4});
  assign key5 = pc2({c5, d5});
  assign key6 = pc2({c6, d6});
  assign key7 = pc2({c7, d7});
  assign key8 = pc2({c8, d8});
  assign key9 = pc2({c9, d9});
  assign key10 = pc2({c10, d10});
  assign key11 = pc2({c11, d11});
  assign key12 = pc2({c12, d12});
  assign key13 = pc2({c13, d13});
  assign key14 = pc2({c14, d14});
  assign key15 = pc2({c15, d15});
  assign key16 = pc2({c16, d16});


endmodule