/* gostdsa-verify.c

   Copyright (C) 2015 Dmitry Eremin-Solenikov

   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 http://www.gnu.org/licenses/.

*/

#if HAVE_CONFIG_H

# include "config.h"

#endif

#include <stdlib.h>

#include "gostdsa.h"

#include "gmp-glue.h"

int

gostdsa_verify (const struct ecc_point *pub,

	      size_t length, const uint8_t *digest,

	      const struct dsa_signature *signature)

{

  mp_limb_t size = ecc_size (pub->ecc);

  mp_size_t itch = 2*size + ecc_gostdsa_verify_itch (pub->ecc);

  /* For ECC_MUL_A_WBITS == 0, at most 1512 bytes. With

     ECC_MUL_A_WBITS == 4, currently needs 67 * ecc->size, at most

     4824 bytes. Don't use stack allocation for this. */

  mp_limb_t *scratch;

  int res;

#define rp scratch

#define sp (scratch + size)

#define scratch_out (scratch + 2*size)

  if (mpz_sgn (signature->r) <= 0 || mpz_size (signature->r) > size

      || mpz_sgn (signature->s) <= 0 || mpz_size (signature->s) > size)

    return 0;

  scratch = gmp_alloc_limbs (itch);

  mpz_limbs_copy (rp, signature->r, size);

  mpz_limbs_copy (sp, signature->s, size);

  res = ecc_gostdsa_verify (pub->ecc, pub->p, length, digest, rp, sp, scratch_out);

  gmp_free_limbs (scratch, itch);

  return res;

#undef rp

#undef sp

#undef scratch_out

}