/* 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://libtomcrypt.com *//* 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_map.c  ECC Crypto, Tom St Denis*/  #ifdef MECC/**  Map a projective jacbobian point back to affine space  @param P        [in/out] The point to map  @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_map(ecc_point *P, void *modulus, void *mp){   void *t1, *t2;   int   err;   LTC_ARGCHK(P       != NULL);   LTC_ARGCHK(modulus != NULL);   LTC_ARGCHK(mp      != NULL);   if ((err = mp_init_multi(&t1, &t2, NULL)) != CRYPT_OK) {      return CRYPT_MEM;   }   /* first map z back to normal */   if ((err = mp_montgomery_reduce(P->z, modulus, mp)) != CRYPT_OK)           { goto done; }   /* get 1/z */   if ((err = mp_invmod(P->z, modulus, t1)) != CRYPT_OK)                      { goto done; }    /* get 1/z^2 and 1/z^3 */   if ((err = mp_sqr(t1, t2)) != CRYPT_OK)                                    { goto done; }   if ((err = mp_mod(t2, modulus, t2)) != CRYPT_OK)                           { goto done; }   if ((err = mp_mul(t1, t2, t1)) != CRYPT_OK)                                { goto done; }   if ((err = mp_mod(t1, modulus, t1)) != CRYPT_OK)                           { goto done; }   /* multiply against x/y */   if ((err = mp_mul(P->x, t2, P->x)) != CRYPT_OK)                            { goto done; }   if ((err = mp_montgomery_reduce(P->x, modulus, mp)) != CRYPT_OK)           { goto done; }   if ((err = mp_mul(P->y, t1, P->y)) != CRYPT_OK)                            { goto done; }   if ((err = mp_montgomery_reduce(P->y, modulus, mp)) != CRYPT_OK)           { goto done; }   if ((err = mp_set(P->z, 1)) != 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_map.c,v $ *//* $Revision: 1.5 $ *//* $Date: 2006/12/04 02:50:11 $ */