lib/nettle/ecc_projective_dbl_point_3.c

   1 /*
   2  * Copyright (C) 2011-2012 Free Software Foundation, Inc.
   3  *
   4  * This file is part of GNUTLS.
   5  *
   6  * The GNUTLS library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public License
   8  * as published by the Free Software Foundation; either version 3 of
   9  * the License, or (at your option) any later version.
  10  *
  11  * This library is distributed in the hope that it will be useful, but
  12  * WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>
  18  *
  19  */
  20
  21 /* Based on public domain code of LibTomCrypt by Tom St Denis.
  22  * Adapted to gmp and nettle by Nikos Mavrogiannopoulos.
  23  */
  24
  25 #include "ecc.h"
  26
  27 /*
  28   @file ecc_projective_dbl_point.c
  29   ECC Crypto, Tom St Denis
  30 */
  31
  32 #ifdef ECC_SECP_CURVES_ONLY
  33
  34 /*
  35    Double an ECC point
  36    @param P   The point to double
  37    @param R   [out] The destination of the double
  38    @param modulus  The modulus of the field the ECC curve is in
  39    @param mp       The "b" value from montgomery_setup()
  40    @return 0 on success
  41 */
  42 int
  43 ecc_projective_dbl_point (ecc_point * P, ecc_point * R, mpz_t a /* a is -3 */,
  44                               mpz_t modulus)
  45 {
  46    mpz_t t1, t2;
  47    int   err;
  48
  49    if (P == NULL || R == NULL || modulus == NULL)
  50      return -1;
  51
  52    if ((err = mp_init_multi(&t1, &t2, NULL)) != 0) {
  53       return err;
  54    }
  55
  56    if (P != R) {
  57       mpz_set(R->x, P->x);
  58       mpz_set(R->y, P->y);
  59       mpz_set(R->z, P->z);
  60    }
  61
  62    /* t1 = Z * Z */
  63    mpz_mul(t1, R->z, R->z);
  64    mpz_mod(t1, t1, modulus);
  65    /* Z = Y * Z */
  66    mpz_mul(R->z, R->y, R->z);
  67    mpz_mod(R->z, R->z, modulus);
  68    /* Z = 2Z */
  69    mpz_add(R->z, R->z, R->z);
  70    if (mpz_cmp(R->z, modulus) >= 0) {
  71       mpz_sub(R->z, R->z, modulus);
  72    }
  73
  74    /* T2 = X - T1 */
  75    mpz_sub(t2, R->x, t1);
  76    if (mpz_cmp_ui(t2, 0) < 0) {
  77       mpz_add(t2, t2, modulus);
  78    }
  79    /* T1 = X + T1 */
  80    mpz_add(t1, t1, R->x);
  81    if (mpz_cmp(t1, modulus) >= 0) {
  82       mpz_sub(t1, t1, modulus);
  83    }
  84    /* T2 = T1 * T2 */
  85    mpz_mul(t2, t1, t2);
  86    mpz_mod(t2, t2, modulus);
  87    /* T1 = 2T2 */
  88    mpz_add(t1, t2, t2);
  89    if (mpz_cmp(t1, modulus) >= 0) {
  90       mpz_sub(t1, t1, modulus);
  91    }
  92    /* T1 = T1 + T2 */
  93    mpz_add(t1, t1, t2);
  94    if (mpz_cmp(t1, modulus) >= 0) {
  95       mpz_sub(t1, t1, modulus);
  96    }
  97
  98    /* Y = 2Y */
  99    mpz_add(R->y, R->y, R->y);
 100    if (mpz_cmp(R->y, modulus) >= 0) {
 101       mpz_sub(R->y, R->y, modulus);
 102    }
 103    /* Y = Y * Y */
 104    mpz_mul(R->y, R->y, R->y);
 105    mpz_mod(R->y, R->y, modulus);
 106    /* T2 = Y * Y */
 107    mpz_mul(t2, R->y, R->y);
 108    mpz_mod(t2, t2, modulus);
 109    /* T2 = T2/2 */
 110    if (mpz_odd_p(t2)) {
 111       mpz_add(t2, t2, modulus);
 112    }
 113    mpz_divexact_ui(t2, t2, 2);
 114    /* Y = Y * X */
 115    mpz_mul(R->y, R->y, R->x);
 116    mpz_mod(R->y, R->y, modulus);
 117
 118    /* X  = T1 * T1 */
 119    mpz_mul(R->x, t1, t1);
 120    mpz_mod(R->x, R->x, modulus);
 121    /* X = X - Y */
 122    mpz_sub(R->x, R->x, R->y);
 123    if (mpz_cmp_ui(R->x, 0) < 0) {
 124       mpz_add(R->x, R->x, modulus);
 125    }
 126    /* X = X - Y */
 127    mpz_sub(R->x, R->x, R->y);
 128    if (mpz_cmp_ui(R->x, 0) < 0) {
 129       mpz_add(R->x, R->x, modulus);
 130    }
 131
 132    /* Y = Y - X */
 133    mpz_sub(R->y, R->y, R->x);
 134    if (mpz_cmp_ui(R->y, 0) < 0) {
 135       mpz_add(R->y, R->y, modulus);
 136    }
 137    /* Y = Y * T1 */
 138    mpz_mul(R->y, R->y, t1);
 139    mpz_mod(R->y, R->y, modulus);
 140    /* Y = Y - T2 */
 141    mpz_sub(R->y, R->y, t2);
 142    if (mpz_cmp_ui(R->y, 0) < 0) {
 143       mpz_add( R->y, R->y, modulus);
 144    }
 145
 146    err = 0;
 147
 148    mp_clear_multi(&t1, &t2, NULL);
 149    return err;
 150 }
 151 #endif
 152 /* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_projective_dbl_point.c,v $ */
 153 /* $Revision: 1.11 $ */
 154 /* $Date: 2007/05/12 14:32:35 $ */
 155