rsa-sec-compute-root.c

/* rsa-sec-compute-root.c

   Side-channel silent RSA root computation.

   Copyright (C) 2018 Niels Möller
   Copyright (C) 2018 Red Hat, Inc

   This file is part of GNU Nettle.

   GNU Nettle is free software: you can redistribute it and/or
   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at your
       option) any later version.

   or

     * the GNU General Public License as published by the Free
       Software Foundation; either version 2 of the License, or (at your
       option) any later version.

   or both in parallel, as here.

   GNU Nettle 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
   General Public License for more details.

   You should have received copies of the GNU General Public License and
   the GNU Lesser General Public License along with this program.  If
   not, see http://www.gnu.org/licenses/.
*/

#if HAVE_CONFIG_H
# include "config.h"
#endif

#include <assert.h>

#include "rsa.h"
#include "rsa-internal.h"
#include "gmp-glue.h"

#if !NETTLE_USE_MINI_GMP
#define MAX(a, b) ((a) > (b) ? (a) : (b))

/* Like mpn_sec_mul_itch, monotonously increasing in operand sizes. */
static mp_size_t
sec_mul_itch (mp_size_t an, mp_size_t bn)
{
  if (an >= bn)
    return mpn_sec_mul_itch (an, bn);
  else
    return mpn_sec_mul_itch (bn, an);
}

/* Writes an + bn limbs to the rp area */
static void
sec_mul (mp_limb_t *rp,
	 const mp_limb_t *ap, mp_size_t an,
	 const mp_limb_t *bp, mp_size_t bn, mp_limb_t *scratch)
{
  if (an >= bn)
    mpn_sec_mul (rp, ap, an, bp, bn, scratch);
  else
    mpn_sec_mul (rp, bp, bn, ap, an, scratch);
}

static mp_size_t