Coverage Report

Created: 2024-06-28 06:39

/src/nettle-with-mini-gmp/ecc-point.c
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/* ecc-point.c
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   Copyright (C) 2013, 2014 Niels Möller
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   This file is part of GNU Nettle.
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   GNU Nettle is free software: you can redistribute it and/or
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   modify it under the terms of either:
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     * the GNU Lesser General Public License as published by the Free
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       Software Foundation; either version 3 of the License, or (at your
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       option) any later version.
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   or
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     * the GNU General Public License as published by the Free
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       Software Foundation; either version 2 of the License, or (at your
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       option) any later version.
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   or both in parallel, as here.
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   GNU Nettle is distributed in the hope that it will be useful,
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   but WITHOUT ANY WARRANTY; without even the implied warranty of
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   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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   General Public License for more details.
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   You should have received copies of the GNU General Public License and
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   the GNU Lesser General Public License along with this program.  If
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   not, see http://www.gnu.org/licenses/.
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*/
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/* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
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#if HAVE_CONFIG_H
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# include "config.h"
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#endif
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#include "ecc.h"
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#include "ecc-internal.h"
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void
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ecc_point_init (struct ecc_point *p, const struct ecc_curve *ecc)
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{
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  p->ecc = ecc;
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  p->p = gmp_alloc_limbs (2*ecc->p.size);
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}
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void
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ecc_point_clear (struct ecc_point *p)
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{
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  gmp_free_limbs (p->p, 2*p->ecc->p.size);
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}
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int
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ecc_point_set (struct ecc_point *p, const mpz_t x, const mpz_t y)
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{
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  mp_size_t size;  
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  mpz_t m, lhs, rhs;
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  mpz_t t;
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  int res;
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  size = p->ecc->p.size;
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  mpz_roinit_n (m, p->ecc->p.m, size);
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  if (mpz_sgn (x) < 0 || mpz_cmp (x, m) >= 0
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      || mpz_sgn (y) < 0 || mpz_cmp (y, m) >= 0)
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    return 0;
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  mpz_init (lhs);
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  mpz_init (rhs);
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  mpz_mul (lhs, y, y);
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  if (p->ecc->p.bit_size == 255)
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0
    {
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      /* ed25519 special case. FIXME: Do in some cleaner way? */
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0
      mpz_t x2;
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      mpz_init (x2);
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      mpz_mul (x2, x, x);
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      mpz_mul (rhs, x2, lhs);
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      /* Check that -x^2 + y^2 = 1 - (121665/121666) x^2 y^2
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   or 121666 (1 + x^2 - y^2) = 121665 x^2 y^2 */
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      mpz_sub (lhs, x2, lhs);
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      mpz_add_ui (lhs, lhs, 1);
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      mpz_mul_ui (lhs, lhs, 121666);
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      mpz_mul_ui (rhs, rhs, 121665);
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      mpz_clear (x2);
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0
    }
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  else if (p->ecc->p.bit_size == 448)
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    {
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      /* curve448 special case. FIXME: Do in some cleaner way? */
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      mpz_t x2, d;
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      mpz_init (x2);
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      mpz_init_set_ui (d, 39081);
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      mpz_mul (x2, x, x); /* x^2 */
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      mpz_mul (d, d, x2); /* 39081 x^2 */
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      mpz_set_ui (rhs, 1);
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      mpz_submul (rhs, d, lhs); /* 1 - 39081 x^2 y^2 */
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      /* Check that x^2 + y^2 = 1 - 39081 x^2 y^2 */
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      mpz_add (lhs, x2, lhs); /* x^2 + y^2 */
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      mpz_clear (d);
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      mpz_clear (x2);
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0
    }
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  else
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    {
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      /* Check that y^2 = x^3 - 3*x + b (mod p) */
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      mpz_mul (rhs, x, x);
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      mpz_sub_ui (rhs, rhs, 3);
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      mpz_mul (rhs, rhs, x);
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      mpz_add (rhs, rhs, mpz_roinit_n (t, p->ecc->b, size));
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    }
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  res = mpz_congruent_p (lhs, rhs, mpz_roinit_n (t, p->ecc->p.m, size));
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  mpz_clear (lhs);
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  mpz_clear (rhs);
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  if (!res)
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    return 0;
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  mpz_limbs_copy (p->p, x, size);
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  mpz_limbs_copy (p->p + size, y, size);
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  return 1;
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}
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void
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ecc_point_get (const struct ecc_point *p, mpz_t x, mpz_t y)
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{
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  mp_size_t size = p->ecc->p.size;
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  if (x)
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    mpz_set_n (x, p->p, size);
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  if (y)
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    mpz_set_n (y, p->p + size, size);
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}