/* Obscurity layer: a "password" for incoming connections.  Use any
   algorithm you want to generate the password.  The example given here
   doubles the current day-of-month and adds to a base constant.

   Don't rely on this alone, of course.  Back it up with something strong
   like an s/keyed login.  This just confuses casual cruisers so they don't
   see your login prompt right away.

   If TELNET is defined, do the turn-off-echo telnet options; otherwise,
   issue a phoney "220" prompt to coerce the client into proceeding.  Your
   FTP client might get slightly out of sync; deal.

   This'll be running as root, so read before you build.

   _H*/

/* Preferably define all these at compile time, depending on your system */
#ifndef _PATH_DAEMON
#define _PATH_DAEMON "/usr/sbin/in.telnetd"	/* linux telnetd*/
#endif
#ifndef PASS
#define PASS 2600	/* snuk snuk */
#endif

#include <syslog.h>
#include <stdio.h>
#include <time.h>

main()
{
unsigned char buf [42];
static char prog[] = _PATH_DAEMON;
unsigned char * bufp;
unsigned int o_day = 0;
unsigned int o_hour = 0;
struct tm * now;
time_t tnow;
char *strrchr();

#ifdef TELNET
/* Tells client telnet to NOT do local echo */
static char prod[] = { 255, 251, 1};		/* IAC WILL ECHO */
  write (0, prod, 3);
#else
/* looks like a generic server thingie */
static char prod[] = "220\r\n";
  write (0, prod, 5);
#endif /* TELNET */

  time (&tnow);
  now = localtime(&tnow);
  o_day = now->tm_mday;

  if (fgets (buf, 40, stdin) > 0) {
    bufp = buf;
    while ((*bufp != '\0') && (!isdigit (*bufp & 0x7F)))
	bufp++;
/* put your algorithm here */
    if (atoi (bufp) != PASS + (o_day * 2)) {
      syslog (LOG_AUTH|LOG_ERR, "refused \"%s\"", buf);
      sleep (20);
      exit (0);
    }

    bufp = strrchr (prog, '/');
    execl (prog, bufp ? bufp : prog, 0);
    exit (0);
  } /* fgets */
}