release/src/router/nettle/ecc-hash.c

   1 /* ecdsa-hash.c */
   2
   3 /* nettle, low-level cryptographics library
   4  *
   5  * Copyright (C) 2013 Niels Möller
   6  *
   7  * The nettle library is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU Lesser General Public License as published by
   9  * the Free Software Foundation; either version 2.1 of the License, or (at your
  10  * option) any later version.
  11  *
  12  * The nettle library is distributed in the hope that it will be useful, but
  13  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  15  * License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public License
  18  * along with the nettle library; see the file COPYING.LIB.  If not, write to
  19  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
  20  * MA 02111-1301, USA.
  21  */
  22
  23 /* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
  24
  25 #if HAVE_CONFIG_H
  26 # include "config.h"
  27 #endif
  28
  29 #include "ecc-internal.h"
  30
  31 /* Convert hash value to an integer. If the digest is larger than
  32    the ecc bit size, then we must truncate it and use the leftmost
  33    bits. */
  34
  35 /* NOTE: We don't considered the hash value to be secret, so it's ok
  36    if the running time of this conversion depends on h.
  37
  38    Requires ecc->size + 1 limbs, the extra limb may be needed for
  39    unusual limb sizes.
  40 */
  41 void
  42 ecc_hash (const struct ecc_curve *ecc,
  43           mp_limb_t *hp,
  44           unsigned length, const uint8_t *digest)
  45 {
  46   if (length > ((unsigned) ecc->bit_size + 7) / 8)
  47     length = (ecc->bit_size + 7) / 8;
  48
  49   mpn_set_base256 (hp, ecc->size + 1, digest, length);
  50
  51   if (8 * length > ecc->bit_size)
  52     /* We got a few extra bits, at the low end. Discard them. */
  53     mpn_rshift (hp, hp, ecc->size + 1, 8*length - ecc->bit_size);
  54 }