rsa-sec-decrypt.c

   1 /* rsa-sec-decrypt.c
   2
   3    RSA decryption, using randomized RSA blinding to be more resistant
   4    to side-channel attacks like timing attacks or cache based memory
   5    access measurements.
   6
   7    Copyright (C) 2001, 2012 Niels Möller, Nikos Mavrogiannopoulos
   8    Copyright (C) 2018 Red Hat, Inc.
   9
  10    This file is part of GNU Nettle.
  11
  12    GNU Nettle is free software: you can redistribute it and/or
  13    modify it under the terms of either:
  14
  15      * the GNU Lesser General Public License as published by the Free
  16        Software Foundation; either version 3 of the License, or (at your
  17        option) any later version.
  18
  19    or
  20
  21      * the GNU General Public License as published by the Free
  22        Software Foundation; either version 2 of the License, or (at your
  23        option) any later version.
  24
  25    or both in parallel, as here.
  26
  27    GNU Nettle is distributed in the hope that it will be useful,
  28    but WITHOUT ANY WARRANTY; without even the implied warranty of
  29    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  30    General Public License for more details.
  31
  32    You should have received copies of the GNU General Public License and
  33    the GNU Lesser General Public License along with this program.  If
  34    not, see http://www.gnu.org/licenses/.
  35 */
  36
  37 #if HAVE_CONFIG_H
  38 # include "config.h"
  39 #endif
  40
  41 #include "rsa.h"
  42 #include "pkcs1-internal.h"
  43 #include "rsa-internal.h"
  44
  45 #include "gmp-glue.h"
  46
  47 int
  48 rsa_sec_decrypt(const struct rsa_public_key *pub,
  49                 const struct rsa_private_key *key,
  50                 void *random_ctx, nettle_random_func *random,
  51                 size_t length, uint8_t *message,
  52                 const mpz_t gibberish)
  53 {
  54   TMP_GMP_DECL (m, mp_limb_t);
  55   TMP_GMP_DECL (em, uint8_t);
  56   int res;
  57
  58   /* First check that input is in range. */
  59   if (mpz_sgn (gibberish) < 0 || mpz_cmp (gibberish, pub->n) >= 0)
  60     return 0;
  61
  62   TMP_GMP_ALLOC (m, mpz_size(pub->n));
  63   TMP_GMP_ALLOC (em, key->size);
  64
  65   /* We need a copy because m can be shorter than key_size,
  66    * but _rsa_sec_compute_root_tr expect all inputs to be
  67    * normalized to a key_size long buffer length */
  68   mpz_limbs_copy(m, gibberish, mpz_size(pub->n));
  69
  70   res = _rsa_sec_compute_root_tr (pub, key, random_ctx, random, m, m);
  71
  72   mpn_get_base256 (em, key->size, m, mpz_size(pub->n));
  73
  74   res &= _pkcs1_sec_decrypt (length, message, key->size, em);
  75
  76   TMP_GMP_FREE (em);
  77   TMP_GMP_FREE (m);
  78   return res;
  79 }
  80