64 lines
2.1 KiB
C
64 lines
2.1 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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#include "tomcrypt_private.h"
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/**
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@file ltc_ecc_map.c
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ECC Crypto, Tom St Denis
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*/
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#ifdef LTC_MECC
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/**
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Map a projective jacbobian point back to affine space
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@param P [in/out] The point to map
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@param modulus The modulus of the field the ECC curve is in
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@param mp The "b" value from montgomery_setup()
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@return CRYPT_OK on success
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*/
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int ltc_ecc_map(ecc_point *P, const void *modulus, void *mp)
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{
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void *t1, *t2;
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int err;
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LTC_ARGCHK(P != NULL);
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LTC_ARGCHK(modulus != NULL);
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LTC_ARGCHK(mp != NULL);
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if (ltc_mp_iszero(P->z)) {
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return ltc_ecc_set_point_xyz(0, 0, 1, P);
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}
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if ((err = ltc_mp_init_multi(&t1, &t2, LTC_NULL)) != CRYPT_OK) {
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return err;
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}
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/* first map z back to normal */
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if ((err = ltc_mp_montgomery_reduce(P->z, modulus, mp)) != CRYPT_OK) { goto done; }
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/* get 1/z */
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if ((err = ltc_mp_invmod(P->z, modulus, t1)) != CRYPT_OK) { goto done; }
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/* get 1/z^2 and 1/z^3 */
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if ((err = ltc_mp_sqr(t1, t2)) != CRYPT_OK) { goto done; }
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if ((err = ltc_mp_mod(t2, modulus, t2)) != CRYPT_OK) { goto done; }
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if ((err = ltc_mp_mul(t1, t2, t1)) != CRYPT_OK) { goto done; }
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if ((err = ltc_mp_mod(t1, modulus, t1)) != CRYPT_OK) { goto done; }
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/* multiply against x/y */
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if ((err = ltc_mp_mul(P->x, t2, P->x)) != CRYPT_OK) { goto done; }
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if ((err = ltc_mp_montgomery_reduce(P->x, modulus, mp)) != CRYPT_OK) { goto done; }
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if ((err = ltc_mp_mul(P->y, t1, P->y)) != CRYPT_OK) { goto done; }
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if ((err = ltc_mp_montgomery_reduce(P->y, modulus, mp)) != CRYPT_OK) { goto done; }
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if ((err = ltc_mp_set(P->z, 1)) != CRYPT_OK) { goto done; }
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err = CRYPT_OK;
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done:
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ltc_mp_deinit_multi(t1, t2, LTC_NULL);
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return err;
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}
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#endif
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