findlc.c

a very popular packet of cryptography tools,it encloses the most common used algorithm and protocols

/*
Copyright 2000 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP 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 2.1 of the License, or (at your
option) any later version.

The GNU MP 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 the GNU MP Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA.
*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <math.h>
#include "gmp.h"
#include "gmpstat.h"

#define RCSID(msg) \
static /**/const char *const rcsid[] = { (char *)rcsid, "\100(#)" msg }

RCSID("$Id: findlc.c,v 1.4 2000/10/14 23:18:06 kevin Exp $");

int g_debug = 0;

static mpz_t a;

static void
sh_status (int sig)
{
  printf ("sh_status: signal %d caught. dumping status.\n", sig);

  printf ("  a = ");
  mpz_out_str (stdout, 10, a);
  printf ("\n");
  fflush (stdout);

  if (SIGSEGV == sig)		/* remove SEGV handler */
    signal (SIGSEGV, SIG_DFL);
}

/* Input is a modulus (m).  We shall find multiplyer (a) and adder (c)
   conforming to the rules found in the first comment block in file
   mpz/urandom.c.

   Then run a spectral test on the generator and discard any
   multipliers not passing.  */

/* TODO:

   . find a better algorithm than a+=8; bigger jumps perhaps?

*/

void
mpz_true_random (mpz_t s, unsigned long int nbits)
{
#if __FreeBSD__
  FILE *fs;
  char c[1];
  int i;

  mpz_set_ui (s, 0);
  for (i = 0; i < nbits; i += 8)
    {
      for (;;)
	{
	  int nread;
	  fs = fopen ("/dev/random", "r");
	  nread = fread (c, 1, 1, fs);
	  fclose (fs);
	  if (nread != 0)
	    break;
	  sleep (1);
	}
      mpz_mul_2exp (s, s, 8);
      mpz_add_ui (s, s, ((unsigned long int) c[0]) & 0xff);
      printf ("%d random bits\n", i + 8);
    }
  if (nbits % 8 != 0)
    mpz_mod_2exp (s, s, nbits);
#endif
}

int
main (int argc, char *argv[])
{
  const char usage[] = "usage: findlc [-dv] m2exp [low_merit [high_merit]]\n";
  int f;
  int v_lose, m_lose, v_best, m_best;
  int c;
  int debug = 1;
  int cnt_high_merit;
  mpz_t m;
  unsigned long int m2exp;
#define DIMS 6			/* dimensions run in spectral test */
  mpf_t v[DIMS-1];		/* spectral test result (there's no v
                                   for 1st dimension */
  mpf_t f_merit, low_merit, high_merit;
  mpz_t acc, minus8;
  mpz_t min, max;
  mpz_t s;


  mpz_init (m);
  mpz_init (a);
  for (f = 0; f < DIMS-1; f++)
    mpf_init (v[f]);
  mpf_init (f_merit);
  mpf_init_set_d (low_merit, .1);
  mpf_init_set_d (high_merit, .1);

  while ((c = getopt (argc, argv, "a:di:hv")) != -1)
    switch (c)
      {
      case 'd':			/* debug */
	g_debug++;
	break;

      case 'v':			/* print version */
	puts (rcsid[1]);
	exit (0);

      case 'h':
      case '?':
      default:
	fputs (usage, stderr);
	exit (1);
      }

  argc -= optind;
  argv += optind;

  if (argc < 1)
    {
      fputs (usage, stderr);
      exit (1);
    }

  /* Install signal handler. */
  if (SIG_ERR == signal (SIGSEGV, sh_status))
    {
      perror ("signal (SIGSEGV)");
      exit (1);
    }
  if (SIG_ERR == signal (SIGHUP, sh_status))
    {
      perror ("signal (SIGHUP)");
      exit (1);
    }

  printf ("findlc: version: %s\n", rcsid[1]);
  m2exp = atol (argv[0]);
  mpz_init_set_ui (m, 1);
  mpz_mul_2exp (m, m, m2exp);
  printf ("m = 0x");
  mpz_out_str (stdout, 16, m);
  puts ("");

  if (argc > 1)			/* have low_merit */
    mpf_set_str (low_merit, argv[1], 0);
  if (argc > 2)			/* have high_merit */
    mpf_set_str (high_merit, argv[2], 0);

  if (debug)
    {
      fprintf (stderr, "low_merit = ");
      mpf_out_str (stderr, 10, 2, low_merit);
      fprintf (stderr, "; high_merit = ");
      mpf_out_str (stderr, 10, 2, high_merit);
      fputs ("\n", stderr);
    }

  mpz_init (minus8);
  mpz_set_si (minus8, -8L);
  mpz_init_set_ui (acc, 0);
  mpz_init (s);
  mpz_init_set_d (min, 0.01 * pow (2.0, (double) m2exp));
  mpz_init_set_d (max, 0.99 * pow (2.0, (double) m2exp));

  mpz_true_random (s, m2exp);	/* Start.  */
  mpz_setbit (s, 0);		/* Make it odd.  */

  v_best = m_best = 2*(DIMS-1);
  for (;;) 
    {
      mpz_add (acc, acc, s);
      mpz_mod_2exp (acc, acc, m2exp);
#if later
      mpz_and_si (a, acc, -8L);
#else
      mpz_and (a, acc, minus8);
#endif
      mpz_add_ui (a, a, 5);
      if (mpz_cmp (a, min) <= 0 || mpz_cmp (a, max) >= 0)
	continue;

      spectral_test (v, DIMS, a, m);
      for (f = 0, v_lose = m_lose = 0, cnt_high_merit = DIMS-1;
	   f < DIMS-1; f++)
	{
	  merit (f_merit, f + 2, v[f], m);

	  if (mpf_cmp_ui (v[f], 1 << (30 / (f + 2) + (f == 2))) < 0)
	    v_lose++;
	    
	  if (mpf_cmp (f_merit, low_merit) < 0)
	    m_lose++;

	  if (mpf_cmp (f_merit, high_merit) >= 0)
	    cnt_high_merit--;
	}

      if (0 == v_lose && 0 == m_lose)
	{
	  mpz_out_str (stdout, 10, a); puts (""); fflush (stdout);
	  if (0 == cnt_high_merit)
	    break;		/* leave loop */
	}
      if (v_lose < v_best)
	{
	  v_best = v_lose;
	  printf ("best (v_lose=%d; m_lose=%d): ", v_lose, m_lose);
	  mpz_out_str (stdout, 10, a); puts (""); fflush (stdout);
	}
      if (m_lose < m_best)
	{
	  m_best = m_lose;
	  printf ("best (v_lose=%d; m_lose=%d): ", v_lose, m_lose);
	  mpz_out_str (stdout, 10, a); puts (""); fflush (stdout);
	}
    }

  mpz_clear (m);
  mpz_clear (a);
  for (f = 0; f < DIMS-1; f++)
    mpf_clear (v[f]);
  mpf_clear (f_merit);
  mpf_clear (low_merit);
  mpf_clear (high_merit);

  printf ("done.\n");
  return 0;
}