Subversion Repositories rc4-prbs

/*

        RC4 PRGA module implementation

        Copyright 2012 - Alfredo Ortega

        aortega@alu.itba.edu.ar

        aortega@groundworkstech.com

 This library 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 3 of the License, or (at your option) any later version.

 This library 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 library.  If not, see <http://www.gnu.org/licenses/>.

*/

`include "rc4.inc"

module rc4(clk,rst,output_ready,password_input,K);

input clk; // Clock

input rst; // Reset

input [7:0] password_input; // Password input

output output_ready; // Output valid

output [7:0] K; // Output port

wire clk, rst; // clock, reset

reg output_ready;

wire [7:0] password_input;

/* RC4 PRGA */

// Key

reg [7:0] key[0:`KEY_SIZE-1];

// S array

reg [7:0] S[0:256];

reg [10:0] discardCount;

// Key-scheduling state

`define KSS_KEYREAD 4'h0

`define KSS_KEYSCHED1 4'h1

`define KSS_KEYSCHED2 4'h2

`define KSS_KEYSCHED3 4'h3

`define KSS_CRYPTO       4'h4

// Variable names from http://en.wikipedia.org/wiki/RC4

reg [3:0] KSState;

reg [7:0] i; // Counter

reg [7:0] j;

reg [7:0] K;

always @ (posedge clk or posedge rst)

        begin

        if (rst)

                begin

                i <= 8'h0;

                KSState <= `KSS_KEYREAD;

                output_ready <= 0;

                j <= 0;

                end

        else

        case (KSState)

                `KSS_KEYREAD:   begin // KSS_KEYREAD state: Read key from input

                                if (i == `KEY_SIZE)

                                        begin

                                        KSState <= `KSS_KEYSCHED1;

                                        i<=8'h00;

                                        end

                                else    begin

                                        i <= i+1;

                                        key[i] <= password_input;

                                        $display ("rc4: key[%d] = %08X",i,password_input);

                                        end

                                end

/*

for i from 0 to 255

    S[i] := i

endfor

*/

                `KSS_KEYSCHED1: begin // KSS_KEYSCHED1: Increment counter for S initialization

                                S[i] <= i;

                                if (i == 8'hFF)

                                        begin

                                        KSState <= `KSS_KEYSCHED2;

                                        i <= 8'h00;

                                        end

                                else    i <= i +1;

                                end

/*

j := 0

for i from 0 to 255

    j := (j + S[i] + key[i mod keylength]) mod 256

    swap values of S[i] and S[j]

endfor

*/

                `KSS_KEYSCHED2: begin // KSS_KEYSCHED2: Initialize S array

                                j <= (j + S[i] + key[i % `KEY_SIZE]);

                                KSState <= `KSS_KEYSCHED3;

                                end

                `KSS_KEYSCHED3: begin // KSS_KEYSCHED3: S array permutation

                                S[i]<=S[j];

                                S[j]<=S[i];

                                if (i == 8'hFF)

                                        begin

                                        KSState <= `KSS_CRYPTO;

                                        i <= 8'h01;

                                        j <= S[1];

                                        discardCount <= 11'h0;

                                        output_ready <= 0; // K not valid yet

                                        end

                                else    begin

                                        i <= i + 1;

                                        KSState <= `KSS_KEYSCHED2;

                                        end

                                end

/*

i := 0

j := 0

while GeneratingOutput:

    i := (i + 1) mod 256

    j := (j + S[i]) mod 256

    swap values of S[i] and S[j]

    K := S[(S[i] + S[j]) mod 256]

    output K

endwhile

*/

                `KSS_CRYPTO: begin

                                S[i] <= S[j];

                                S[j] <= S[i]; // We can do this because of verilog.

                                K <= S[ S[i]+S[j] ];

                                if (discardCount<11'h600) // discard first 1536 values / RFC 4345

                                        discardCount<=discardCount+1;

                                else    output_ready <= 1; // Valid K at output

                                i <= i+1;

                                // Here is the secret of 1-clock: we develop all possible values of j in the future

                                if (j==i+1)

                                     j <= (j + S[i]);

                                else

                                        if (i==255) j <= (j + S[0]);

                                                else j <= (j + S[i+1]);

                                //$display ("rc4: output = %08X",K);

                                end

                default:        begin

                                end

        endcase

        end

endmodule