/* ecdsa-hash.c */
/* nettle, low-level cryptographics library
*
* Copyright (C) 2013 Niels MÃ¶ller
*
* The nettle library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at your
* option) any later version.
*
* The nettle library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02111-1301, USA.
*/
/* Development of Nettle's ECC support was funded by Internetfonden. */
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include "ecc-internal.h"
#include "gmp-glue.h"
/* Convert hash value to an integer. If the digest is larger than
the ecc bit size, then we must truncate it and use the leftmost
bits. */
/* NOTE: We don't considered the hash value to be secret, so it's ok
if the running time of this conversion depends on h.
Requires ecc->size + 1 limbs, the extra limb may be needed for
unusual limb sizes.
*/
void
ecc_hash (const struct ecc_curve *ecc,
mp_limb_t *hp,
unsigned length, const uint8_t *digest)
{
if (length > ((unsigned) ecc->bit_size + 7) / 8)
length = (ecc->bit_size + 7) / 8;
_mpn_set_base256 (hp, ecc->size + 1, digest, length);
if (8 * length > ecc->bit_size)
/* We got a few extra bits, at the low end. Discard them. */
mpn_rshift (hp, hp, ecc->size + 1, 8*length - ecc->bit_size);
}