glibc/manual/examples/genpass.c

#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <crypt.h>

int 
main(void)
{
  unsigned long seed[2];
  char salt[] = "$1$........";
  const char *const seedchars = 
    "./0123456789ABCDEFGHIJKLMNOPQRST"
    "UVWXYZabcdefghijklmnopqrstuvwxyz";
  char *password;
  int i;
  
  /* Generate a (not very) random seed.  
     You should do it better than this...  */
  seed[0] = time(NULL);
  seed[1] = getpid() ^ (seed[0] >> 14 & 0x30000);
  
  /* Turn it into printable characters from `seedchars'.  */
  for (i = 0; i < 8; i++)
    salt[3+i] = seedchars[(seed[i/5] >> (i%5)*6) & 0x3f];
  
  /* Read in the user's password and encrypt it.  */
  password = crypt(getpass("Password:"), salt);
  
  /* Print the results.  */
  puts(password);
  return 0;
}