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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://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 $ */
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