| // SPDX-License-Identifier: BSD-2-Clause |
| /* 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. |
| */ |
| |
| #include "tomcrypt_private.h" |
| |
| /** |
| @file ltc_ecc_map.c |
| ECC Crypto, Tom St Denis |
| */ |
| |
| #ifdef LTC_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 (mp_iszero(P->z)) { |
| return ltc_ecc_set_point_xyz(0, 0, 1, P); |
| } |
| |
| if ((err = mp_init_multi(&t1, &t2, NULL)) != CRYPT_OK) { |
| return err; |
| } |
| |
| /* 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 |
| |
| /* ref: $Format:%D$ */ |
| /* git commit: $Format:%H$ */ |
| /* commit time: $Format:%ai$ */ |
| |