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ltc_ecc_projective_dbl_point.c
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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
 *
 * LibTomCrypt is a library that provides various cryptographic
 * algorithms in a highly modular and flexible manner.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 *
 * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
 */

/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
 *
 * All curves taken from NIST recommendation paper of July 1999
 * Available at http://csrc.nist.gov/cryptval/dss.htm
 */
#include "tomcrypt.h"

/**
  @file ltc_ecc_projective_dbl_point.c
  ECC Crypto, Tom St Denis
*/  

#if defined(LTC_MECC) && (!defined(LTC_MECC_ACCEL) || defined(LTM_LTC_DESC))

/**
   Double an ECC point
   @param P   The point to double
   @param R   [out] The destination of the double
   @param modulus  The modulus of the field the ECC curve is in
   @param mp       The "b" value from montgomery_setup()
   @return CRYPT_OK on success
*/
int ltc_ecc_projective_dbl_point(ecc_point *P, ecc_point *R, void *modulus, void *mp)
{
   void *t1, *t2;
   int   err;

   LTC_ARGCHK(P       != NULL);
   LTC_ARGCHK(R       != NULL);
   LTC_ARGCHK(modulus != NULL);
   LTC_ARGCHK(mp      != NULL);

   if ((err = mp_init_multi(&t1, &t2, NULL)) != CRYPT_OK) {
      return err;
   }

   if (P != R) {
      if ((err = mp_copy(P->x, R->x)) != CRYPT_OK)                                { goto done; }
      if ((err = mp_copy(P->y, R->y)) != CRYPT_OK)                                { goto done; }
      if ((err = mp_copy(P->z, R->z)) != CRYPT_OK)                                { goto done; }
   }

   /* t1 = Z * Z */
   if ((err = mp_sqr(R->z, t1)) != CRYPT_OK)                                      { goto done; }
   if ((err = mp_montgomery_reduce(t1, modulus, mp)) != CRYPT_OK)                 { goto done; }
   /* Z = Y * Z */
   if ((err = mp_mul(R->z, R->y, R->z)) != CRYPT_OK)                              { goto done; }
   if ((err = mp_montgomery_reduce(R->z, modulus, mp)) != CRYPT_OK)               { goto done; }
   /* Z = 2Z */
   if ((err = mp_add(R->z, R->z, R->z)) != CRYPT_OK)                              { goto done; }
   if (mp_cmp(R->z, modulus) != LTC_MP_LT) {
      if ((err = mp_sub(R->z, modulus, R->z)) != CRYPT_OK)                        { goto done; }
   }
   
   /* T2 = X - T1 */
   if ((err = mp_sub(R->x, t1, t2)) != CRYPT_OK)                                  { goto done; }
   if (mp_cmp_d(t2, 0) == LTC_MP_LT) {
      if ((err = mp_add(t2, modulus, t2)) != CRYPT_OK)                            { goto done; }
   }
   /* T1 = X + T1 */
   if ((err = mp_add(t1, R->x, t1)) != CRYPT_OK)                                  { goto done; }
   if (mp_cmp(t1, modulus) != LTC_MP_LT) {
      if ((err = mp_sub(t1, modulus, t1)) != CRYPT_OK)                            { goto done; }
   }
   /* T2 = T1 * T2 */
   if ((err = mp_mul(t1, t2, t2)) != CRYPT_OK)                                    { goto done; }
   if ((err = mp_montgomery_reduce(t2, modulus, mp)) != CRYPT_OK)                 { goto done; }
   /* T1 = 2T2 */
   if ((err = mp_add(t2, t2, t1)) != CRYPT_OK)                                    { goto done; }
   if (mp_cmp(t1, modulus) != LTC_MP_LT) {
      if ((err = mp_sub(t1, modulus, t1)) != CRYPT_OK)                            { goto done; }
   }
   /* T1 = T1 + T2 */
   if ((err = mp_add(t1, t2, t1)) != CRYPT_OK)                                    { goto done; }
   if (mp_cmp(t1, modulus) != LTC_MP_LT) {
      if ((err = mp_sub(t1, modulus, t1)) != CRYPT_OK)                            { goto done; }
   }

   /* Y = 2Y */
   if ((err = mp_add(R->y, R->y, R->y)) != CRYPT_OK)                              { goto done; }
   if (mp_cmp(R->y, modulus) != LTC_MP_LT) {
      if ((err = mp_sub(R->y, modulus, R->y)) != CRYPT_OK)                        { goto done; }
   }
   /* Y = Y * Y */
   if ((err = mp_sqr(R->y, R->y)) != CRYPT_OK)                                    { goto done; }
   if ((err = mp_montgomery_reduce(R->y, modulus, mp)) != CRYPT_OK)               { goto done; }
   /* T2 = Y * Y */
   if ((err = mp_sqr(R->y, t2)) != CRYPT_OK)                                      { goto done; }
   if ((err = mp_montgomery_reduce(t2, modulus, mp)) != CRYPT_OK)                 { goto done; }
   /* T2 = T2/2 */
   if (mp_isodd(t2)) {
      if ((err = mp_add(t2, modulus, t2)) != CRYPT_OK)                            { goto done; }
   }
   if ((err = mp_div_2(t2, t2)) != CRYPT_OK)                                      { goto done; }
   /* Y = Y * X */
   if ((err = mp_mul(R->y, R->x, R->y)) != CRYPT_OK)                              { goto done; }
   if ((err = mp_montgomery_reduce(R->y, modulus, mp)) != CRYPT_OK)               { goto done; }

   /* X  = T1 * T1 */
   if ((err = mp_sqr(t1, R->x)) != CRYPT_OK)                                      { goto done; }
   if ((err = mp_montgomery_reduce(R->x, modulus, mp)) != CRYPT_OK)               { goto done; }
   /* X = X - Y */
   if ((err = mp_sub(R->x, R->y, R->x)) != CRYPT_OK)                              { goto done; }
   if (mp_cmp_d(R->x, 0) == LTC_MP_LT) {
      if ((err = mp_add(R->x, modulus, R->x)) != CRYPT_OK)                        { goto done; }
   }
   /* X = X - Y */
   if ((err = mp_sub(R->x, R->y, R->x)) != CRYPT_OK)                              { goto done; }
   if (mp_cmp_d(R->x, 0) == LTC_MP_LT) {
      if ((err = mp_add(R->x, modulus, R->x)) != CRYPT_OK)                        { goto done; }
   }

   /* Y = Y - X */     
   if ((err = mp_sub(R->y, R->x, R->y)) != CRYPT_OK)                              { goto done; }
   if (mp_cmp_d(R->y, 0) == LTC_MP_LT) {
      if ((err = mp_add(R->y, modulus, R->y)) != CRYPT_OK)                        { goto done; }
   }
   /* Y = Y * T1 */
   if ((err = mp_mul(R->y, t1, R->y)) != CRYPT_OK)                                { goto done; }
   if ((err = mp_montgomery_reduce(R->y, modulus, mp)) != CRYPT_OK)               { goto done; }
   /* Y = Y - T2 */
   if ((err = mp_sub(R->y, t2, R->y)) != CRYPT_OK)                                { goto done; }
   if (mp_cmp_d(R->y, 0) == LTC_MP_LT) {
      if ((err = mp_add(R->y, modulus, R->y)) != CRYPT_OK)                        { goto done; }
   }
 
   err = CRYPT_OK;
done:
   mp_clear_multi(t1, t2, NULL);
   return err;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ltc_ecc_projective_dbl_point.c,v $ */
/* $Revision: 1.11 $ */
/* $Date: 2007/05/12 14:32:35 $ */


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