Exemple #1
0
/* Check if N is a prime and G a generator of the
 * group. This is check only done if N is big enough.
 * Otherwise only the included parameters must be used.
 */
static int
group_check_g_n (mpi_t g, mpi_t n)
{
  mpi_t q = NULL, two = NULL, w = NULL;
  int ret;

  if (_gnutls_mpi_get_nbits (n) < 2048)
    {
      gnutls_assert ();
      return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
    }

  /* N must be of the form N=2q+1
   * where q is also a prime.
   */
  if (_gnutls_prime_check (n, 0) != 0)
    {
      _gnutls_dump_mpi ("no prime N: ", n);
      gnutls_assert ();
      return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
    }

  two = _gnutls_mpi_new (4);
  if (two == NULL)
    {
      gnutls_assert ();
      return GNUTLS_E_MEMORY_ERROR;
    }

  q = _gnutls_mpi_alloc_like (n);
  if (q == NULL)
    {
      gnutls_assert ();
      ret = GNUTLS_E_MEMORY_ERROR;
      goto error;
    }

  /* q = n-1 
   */
  _gnutls_mpi_sub_ui (q, n, 1);

  /* q = q/2, remember that q is divisible by 2 (prime - 1)
   */
  _gnutls_mpi_set_ui (two, 2);
  _gnutls_mpi_div (q, NULL, q, two, 0);

  if (_gnutls_prime_check (q, 0) != 0)
    {
      /* N was not on the form N=2q+1, where q = prime
       */
      _gnutls_dump_mpi ("no prime Q: ", q);
      gnutls_assert ();
      return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
    }

  /* We also check whether g is a generator,
   */

  /* check if g < q < N
   */
  if (_gnutls_mpi_cmp (g, q) >= 0)
    {
      gnutls_assert ();
      ret = GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
      goto error;
    }

  w = _gnutls_mpi_alloc_like (q);
  if (w == NULL)
    {
      gnutls_assert ();
      ret = GNUTLS_E_MEMORY_ERROR;
      goto error;
    }

  /* check if g^q mod N == N-1
   * w = g^q mod N
   */
  _gnutls_mpi_powm (w, g, q, n);

  /* w++
   */
  _gnutls_mpi_add_ui (w, w, 1);

  if (_gnutls_mpi_cmp (w, n) != 0)
    {
      gnutls_assert ();
      ret = GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
      goto error;
    }

  ret = 0;

error:
  _gnutls_mpi_release (&q);
  _gnutls_mpi_release (&two);
  _gnutls_mpi_release (&w);

  return ret;

}
Exemple #2
0
/* Check if N is a prime and G a generator of the
 * group. This check is only done if N is big enough.
 * Otherwise only the included parameters must be used.
 */
static int
group_check_g_n(gnutls_session_t session, bigint_t g, bigint_t n)
{
	bigint_t q = NULL, two = NULL, w = NULL;
	int ret;

	if (_gnutls_mpi_get_nbits(n) < (session->internals.srp_prime_bits
					? session->internals.srp_prime_bits
					: 2048)) {
		gnutls_assert();
		return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
	}

	/* N must be of the form N=2q+1
	 * where q is also a prime.
	 */
	if (_gnutls_prime_check(n) != 0) {
		_gnutls_mpi_log("no prime N: ", n);
		gnutls_assert();
		return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
	}

	ret = _gnutls_mpi_init_multi(&two, &q, &w, NULL);
	if (ret < 0) {
		gnutls_assert();
		return ret;
	}

	/* q = n-1 
	 */
	ret = _gnutls_mpi_sub_ui(q, n, 1);
	if (ret < 0) {
		gnutls_assert();
		goto error;
	}

	/* q = q/2, remember that q is divisible by 2 (prime - 1)
	 */
	ret = _gnutls_mpi_set_ui(two, 2);
	if (ret < 0) {
		gnutls_assert();
		goto error;
	}

	ret = _gnutls_mpi_div(q, q, two);
	if (ret < 0) {
		gnutls_assert();
		goto error;
	}

	if (_gnutls_prime_check(q) != 0) {
		/* N was not on the form N=2q+1, where q = prime
		 */
		_gnutls_mpi_log("no prime Q: ", q);
		gnutls_assert();
		ret = GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
		goto error;
	}

	/* We also check whether g is a generator,
	 */

	/* check if g < q < N
	 */
	if (_gnutls_mpi_cmp(g, q) >= 0) {
		gnutls_assert();
		ret = GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
		goto error;
	}

	/* check if g^q mod N == N-1
	 * w = g^q mod N
	 */
	ret = _gnutls_mpi_powm(w, g, q, n);
	if (ret < 0) {
		gnutls_assert();
		goto error;
	}

	/* w++
	 */
	ret = _gnutls_mpi_add_ui(w, w, 1);
	if (ret < 0) {
		gnutls_assert();
		goto error;
	}

	if (_gnutls_mpi_cmp(w, n) != 0) {
		gnutls_assert();
		ret = GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
		goto error;
	}

	ret = 0;

      error:
	_gnutls_mpi_release(&q);
	_gnutls_mpi_release(&two);
	_gnutls_mpi_release(&w);

	return ret;

}