/* rsa-sec-decrypt.c

   RSA decryption, using randomized RSA blinding to be more resistant

   to side-channel attacks like timing attacks or cache based memory

   access measurements.

   Copyright (C) 2001, 2012 Niels Möller, Nikos Mavrogiannopoulos

   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 "rsa.h"

#include "pkcs1-internal.h"

#include "rsa-internal.h"

#include "gmp-glue.h"

int

rsa_sec_decrypt(const struct rsa_public_key *pub,

          const struct rsa_private_key *key,

          void *random_ctx, nettle_random_func *random,

          size_t length, uint8_t *message,

          const mpz_t gibberish)

{

  TMP_GMP_DECL (m, mp_limb_t);

  TMP_GMP_DECL (em, uint8_t);

  int res;

  /* First check that input is in range. */

  if (mpz_sgn (gibberish) < 0 || mpz_cmp (gibberish, pub->n) >= 0)

    return 0;

  TMP_GMP_ALLOC (m, mpz_size(pub->n));

  TMP_GMP_ALLOC (em, key->size);

  /* We need a copy because m can be shorter than key_size,

   * but _rsa_sec_compute_root_tr expect all inputs to be

   * normalized to a key_size long buffer length */

  mpz_limbs_copy(m, gibberish, mpz_size(pub->n));

  res = _rsa_sec_compute_root_tr (pub, key, random_ctx, random, m, m);

  mpn_get_base256 (em, key->size, m, mpz_size(pub->n));

  res &= _pkcs1_sec_decrypt (length, message, key->size, em);

  TMP_GMP_FREE (em);

  TMP_GMP_FREE (m);

  return res;

}