Random password generation3 using /dev/random

/* Secure random password generation via /dev/random */
/* James Hess  Copyright (C) 2011, 2012;  All Rights Reserved */

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
#include <sys/time.h>

             /* Number of entropy buffers to require for each byte of secret generated  (More = longer wait) */
#define     _EXTRA_ITERATIONS 3

            /* Number bytes entropy to require for 1 iteration on each byte of secret generated  (More = longer wait) */
#define     _ENTROPY_BUFSIZE 8

/* You should replace this with a system-specific value*/
static char _EXTRA_SECRET[] = "fido&9uct>_^/38:u{E$43ikOrQS{R9ln2L/f]cqlr1ce9-MviXIWn4dk[nBv2<xu\"kiL!xY;Ps5ez&Ec8^*^P[]I8nQeu12xk*lys69L-Tfi8lRmx1]]/a|";

int main(argc,argv)
  int argc;  char *argv[];
{
   char buf[_ENTROPY_BUFSIZE] = "", junk[80], *f;   /* Buffer to read file data into */

                 /* Buffer size, default password length */
   int bufsize = sizeof(buf), passlen = 15, m;
   struct timeval tv1, tv2;
   clock_t cl1 = clock(), cl2 = 0, cl3=0;

                 /* Repeat XOR this many random values per password character */
   int repeats = _EXTRA_ITERATIONS;

   /*  List of characters to use in passwords */
    //char maptop[] = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_-.,/~!#$%^&*()+=[]{}|;:\"<>/";
   //char maptop[] = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
   char maptop[]   = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
   int maptop_size = sizeof maptop;

   unsigned char random_byteval;
   int i, j, k;

   /* Open /dev/random */
   FILE* fp = fopen("/dev/random","r");

   if (argv && argc > 1 && argv[1] && (j = atoi(argv[1])) && 0 < passlen  )
       passlen = j;

   if (fread(buf, bufsize, 1, fp) < 1 ) {
       perror("fread");
       return 1;
   }

   gettimeofday(&tv1, NULL);
   puts("Press [ENTER] to continue");
   fgets(junk, 10, stdin);
   gettimeofday(&tv2, NULL);
   cl2 = clock();

   for(m = 4; m < bufsize; m++)
       buf[(m - 4)%4] ^= buf[m];

   cl3 = cl2 - cl1 + time(0);
   for (i = 0, f = (char *)&cl3; f <  ( sizeof(clock_t) + (char *)&cl3); buf[i] ^= (*f), i++, f++  ) ;

   srandom( buf[0] | (buf[1] << 8) | (buf[2] << 16) || (buf[3] << 24) );


   if (fp) {
     for(i = 0; i < passlen; i++) {
         cl3 = clock() - cl3;
         for (f = (char *)&cl1; f <  ( sizeof(clock_t) + (char *)&cl1); random_byteval ^= (*f),        f++  ) ;
         for (f = (char *)&cl2; f <  ( sizeof(clock_t) + (char *)&cl2); random_byteval ^= (*f),        f++  ) ;
         for (f = (char *)&cl3; f <  ( sizeof(clock_t) + (char *)&cl3); random_byteval ^= (*f),        f++  ) ;
         for (f = (char *)&tv1; f < ((char *)&tv1 + sizeof(struct timeval));  random_byteval ^= (*f),  f++  ) ;
         for (f = (char *)&tv2; f <  ( (char *)&tv2 + sizeof(struct timeval)); random_byteval ^= (*f), f++  ) ;

       /* Read in that a buffer full of random bytes,  and XOR each byte together */
       /* repeat 'repeats'  time, for each  password character to be generated  */

       for(k = 0; k < repeats; k++) {
          if (  fread(buf, bufsize, 1, fp)  >= 1 ) {
              for(j = 0; j < sizeof(_EXTRA_SECRET); j++)
                  random_byteval ^= _EXTRA_SECRET[j] ^ (char)random();

              for(j = 0 ; j < bufsize ; j++) {
                  random_byteval ^= buf[j] ^ (char)random();
              }
           } else {
              perror("fread");
          exit(0);
          }
       }

       /* pick a password character in the chosen character set. */
       printf("%c", maptop[ random_byteval % maptop_size ]  );

     }
   } else  perror("fopen");

   memset(_EXTRA_SECRET, 0, sizeof(_EXTRA_SECRET));
   memset(buf, 0, sizeof(buf));
   srandom(0);
   random_byteval = 0;
   cl1 = cl2 = cl3 = 0;
   memset(&tv1, 0, sizeof(struct timeval) );
   memset(&tv2, 0, sizeof(struct timeval) );
   puts("");
   puts("Press [ENTER] to clear screen");
   fgets(junk, 10, stdin);
   printf("\e[H\e[J\nDone.\n");

   puts("");
}

/*
Copyright (c) 2013  James Hess
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. 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.
3. All advertising materials mentioning features or use of this software
   must display the following acknowledgement:
   This product includes software developed by James Hess.
4. Neither the name of the organization 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 ''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 <COPYRIGHT HOLDER> 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.
*/