release/src/router/nettle/ecc-point.c

   1 /* ecc-point.c */
   2
   3 /* nettle, low-level cryptographics library
   4  *
   5  * Copyright (C) 2013 Niels Möller
   6  *
   7  * The nettle library is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU Lesser General Public License as published by
   9  * the Free Software Foundation; either version 2.1 of the License, or (at your
  10  * option) any later version.
  11  *
  12  * The nettle library is distributed in the hope that it will be useful, but
  13  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  15  * License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public License
  18  * along with the nettle library; see the file COPYING.LIB.  If not, write to
  19  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
  20  * MA 02111-1301, USA.
  21  */
  22
  23 /* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
  24
  25 #if HAVE_CONFIG_H
  26 # include "config.h"
  27 #endif
  28
  29 #include "ecc.h"
  30 #include "ecc-internal.h"
  31
  32 void
  33 ecc_point_init (struct ecc_point *p, const struct ecc_curve *ecc)
  34 {
  35   p->ecc = ecc;
  36   p->p = gmp_alloc_limbs (2*ecc->size);
  37 }
  38
  39 void
  40 ecc_point_clear (struct ecc_point *p)
  41 {
  42   gmp_free_limbs (p->p, 2*p->ecc->size);
  43 }
  44
  45 int
  46 ecc_point_set (struct ecc_point *p, const mpz_t x, const mpz_t y)
  47 {
  48   mp_size_t size;
  49   mpz_t lhs, rhs;
  50   mpz_t t;
  51   int res;
  52
  53   size = p->ecc->size;
  54
  55   if (mpz_sgn (x) < 0 || mpz_limbs_cmp (x, p->ecc->p, size) >= 0
  56       || mpz_sgn (y) < 0 || mpz_limbs_cmp (y, p->ecc->p, size) >= 0)
  57     return 0;
  58
  59   mpz_init (lhs);
  60   mpz_init (rhs);
  61
  62   /* Check that y^2 = x^3 - 3*x + b (mod p) */
  63   mpz_mul (lhs, y, y);
  64   mpz_mul (rhs, x, x);
  65   mpz_sub_ui (rhs, rhs, 3);
  66   mpz_mul (rhs, rhs, x);
  67   mpz_add (rhs, rhs, mpz_roinit_n (t, p->ecc->b, size));
  68
  69   res = mpz_congruent_p (lhs, rhs, mpz_roinit_n (t, p->ecc->p, size));
  70
  71   mpz_clear (lhs);
  72   mpz_clear (rhs);
  73
  74   if (!res)
  75     return 0;
  76
  77   mpz_limbs_copy (p->p, x, size);
  78   mpz_limbs_copy (p->p + size, y, size);
  79
  80   return 1;
  81 }
  82
  83 void
  84 ecc_point_get (const struct ecc_point *p, mpz_t x, mpz_t y)
  85 {
  86   mp_size_t size = p->ecc->size;
  87   if (x)
  88     mpz_set_n (x, p->p, size);
  89   if (y)
  90     mpz_set_n (y, p->p + size, size);
  91 }