/* ecdsa-sign.c */

/* nettle, low-level cryptographics library
 *
 * Copyright (C) 2013 Niels Möller
 *
 * 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 <assert.h>
#include <stdlib.h>

#include "ecdsa.h"
#include "ecc-internal.h"
#include "gmp-glue.h"
#include "nettle-internal.h"

void
ecdsa_sign (const struct ecc_scalar *key,
	    void *random_ctx, nettle_random_func *random,
	    unsigned digest_length,
	    const uint8_t *digest,
	    struct dsa_signature *signature)
{
  /* At most 936 bytes. */
  TMP_DECL(k, mp_limb_t, ECC_MAX_SIZE + ECC_ECDSA_SIGN_ITCH (ECC_MAX_SIZE));
  mp_limb_t size = key->ecc->size;
  mp_limb_t *rp = mpz_limbs_write (signature->r, size);
  mp_limb_t *sp = mpz_limbs_write (signature->s, size);

  TMP_ALLOC (k, size + ECC_ECDSA_SIGN_ITCH (size));

  /* Timing reveals the number of rounds through this loop, but the
     timing is still independent of the secret k finally used. */
  do
    {
      ecc_modq_random (key->ecc, k, random_ctx, random, k + size);
      ecc_ecdsa_sign (key->ecc, key->p, k, digest_length, digest,
		   rp, sp, k + size);
      mpz_limbs_finish (signature->r, size);
      mpz_limbs_finish (signature->s, size);
    }
  while (mpz_sgn (signature->r) == 0 || mpz_sgn (signature->s) == 0);
}