release/src/router/nettle/rsa-blind.c

   1 /* rsa-blind.c
   2  *
   3  * RSA blinding. It is used for timing resistant decryption or signing.
   4  */
   5
   6 /* nettle, low-level cryptographics library
   7  *
   8  * Copyright (C) 2001, 2012 Niels Möller, Nikos Mavrogiannopoulos
   9  *
  10  * The nettle library is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU Lesser General Public License as published by
  12  * the Free Software Foundation; either version 2.1 of the License, or (at your
  13  * option) any later version.
  14  *
  15  * The nettle library is distributed in the hope that it will be useful, but
  16  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  17  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  18  * License for more details.
  19  *
  20  * You should have received a copy of the GNU Lesser General Public License
  21  * along with the nettle library; see the file COPYING.LIB.  If not, write to
  22  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
  23  * MA 02111-1301, USA.
  24  */
  25
  26 #if HAVE_CONFIG_H
  27 # include "config.h"
  28 #endif
  29
  30 #include "rsa.h"
  31
  32 #include "bignum.h"
  33
  34 /* Blinds the c, by computing c *= r^e (mod n), for a random r. Also
  35    returns the inverse (ri), for use by rsa_unblind. */
  36 void
  37 _rsa_blind (const struct rsa_public_key *pub,
  38             void *random_ctx, nettle_random_func *random,
  39             mpz_t c, mpz_t ri)
  40 {
  41   mpz_t r;
  42
  43   mpz_init(r);
  44
  45   /* c = c*(r^e)
  46    * ri = r^(-1)
  47    */
  48   do
  49     {
  50       nettle_mpz_random(r, random_ctx, random, pub->n);
  51       /* invert r */
  52     }
  53   while (!mpz_invert (ri, r, pub->n));
  54
  55   /* c = c*(r^e) mod n */
  56   mpz_powm(r, r, pub->e, pub->n);
  57   mpz_mul(c, c, r);
  58   mpz_fdiv_r(c, c, pub->n);
  59
  60   mpz_clear(r);
  61 }
  62
  63 /* c *= ri mod n */
  64 void
  65 _rsa_unblind (const struct rsa_public_key *pub, mpz_t c, const mpz_t ri)
  66 {
  67   mpz_mul(c, c, ri);
  68   mpz_fdiv_r(c, c, pub->n);
  69 }