/* ecdsa-hash.c

   Copyright (C) 2013 Niels Möller

   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 https://www.gnu.org/licenses/.

*/

/* Development of Nettle's ECC support was funded by the .SE Internet Fund. */

#if HAVE_CONFIG_H

# include "config.h"

#endif

#include <gnutls_int.h>

#include "ecc/ecc-internal.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 m->size + 1 limbs, the extra limb may be needed for

   unusual limb sizes.

*/

void

gost_hash (const struct ecc_modulo *m,

	   mp_limb_t *hp,

	   size_t length, const uint8_t *digest)

{

  if (length > ((size_t) m->bit_size + 7) / 8)

    length = (m->bit_size + 7) / 8;

  mpn_set_base256_le (hp, m->size + 1, digest, length);

  if (8 * length > m->bit_size)

    /* We got a few extra bits, at the low end. Discard them. */

    mpn_rshift (hp, hp, m->size + 1, 8*length - m->bit_size);

}