/* ecc-ecdsa-sign.c

   Copyright (C) 2013, 2014 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/.

*/

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

#if HAVE_CONFIG_H

# include "config.h"

#endif

#include <assert.h>

#include <stdlib.h>

#include "ecdsa.h"

#include "ecc-internal.h"

/* Low-level ECDSA signing */

mp_size_t

ecc_ecdsa_sign_itch (const struct ecc_curve *ecc)

{

  /* Needs 3*ecc->p.size + scratch for ecc_mul_g. */

  assert (ecc->p.size + ecc->p.invert_itch

    <= 3*ecc->p.size + ECC_MUL_G_ITCH (ecc->p.size));

  return ECC_ECDSA_SIGN_ITCH (ecc->p.size);

}

/* NOTE: Caller should check if r or s is zero. */

void

ecc_ecdsa_sign (const struct ecc_curve *ecc,

    const mp_limb_t *zp,

    /* Random nonce, must be invertible mod ecc group

       order. */

    const mp_limb_t *kp,

    size_t length, const uint8_t *digest,

    mp_limb_t *rp, mp_limb_t *sp,

    mp_limb_t *scratch)

{

#define P     scratch

#define kinv      scratch

#define hp      (scratch  + ecc->p.size) /* NOTE: ecc->p.size + 1 limbs! */

#define tp      (scratch + 2*ecc->p.size)

  /* Procedure, according to RFC 6090, "KT-I". q denotes the group

     order.

     1. k <-- uniformly random, 0 < k < q

     2. R <-- (r_x, r_y) = k g

     3. s1 <-- r_x mod q

     4. s2 <-- (h + z*s1)/k mod q.

  */

  ecc_mul_g (ecc, P, kp, P + 3*ecc->p.size);

  /* x coordinate only, modulo q */

  ecc_j_to_a (ecc, 2, rp, P, P + 3*ecc->p.size);

  /* Invert k, uses up to 7 * ecc->p.size including scratch (for secp384). */

  ecc->q.invert (&ecc->q, kinv, kp, tp);

  /* Process hash digest */

  ecc_hash (&ecc->q, hp, length, digest);

  ecc_mod_mul (&ecc->q, tp, zp, rp, tp);

  ecc_mod_add (&ecc->q, hp, hp, tp);

  ecc_mod_mul_canonical (&ecc->q, sp, hp, kinv, tp);

#undef P

#undef hp

#undef kinv

#undef tp

}