Mercurial > dropbear
view libtommath/bn_mp_prime_fermat.c @ 1692:1051e4eea25a
Update LibTomMath to 1.2.0 (#84)
* update C files
* update other files
* update headers
* update makefiles
* remove mp_set/get_double()
* use ltm 1.2.0 API
* update ltm_desc
* use bundled tommath if system-tommath is too old
* XMALLOC etc. were changed to MP_MALLOC etc.
author | Steffen Jaeckel <s@jaeckel.eu> |
---|---|
date | Tue, 26 May 2020 17:36:47 +0200 |
parents | f52919ffd3b1 |
children |
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#include "tommath_private.h" #ifdef BN_MP_PRIME_FERMAT_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ /* performs one Fermat test. * * If "a" were prime then b**a == b (mod a) since the order of * the multiplicative sub-group would be phi(a) = a-1. That means * it would be the same as b**(a mod (a-1)) == b**1 == b (mod a). * * Sets result to 1 if the congruence holds, or zero otherwise. */ mp_err mp_prime_fermat(const mp_int *a, const mp_int *b, mp_bool *result) { mp_int t; mp_err err; /* default to composite */ *result = MP_NO; /* ensure b > 1 */ if (mp_cmp_d(b, 1uL) != MP_GT) { return MP_VAL; } /* init t */ if ((err = mp_init(&t)) != MP_OKAY) { return err; } /* compute t = b**a mod a */ if ((err = mp_exptmod(b, a, a, &t)) != MP_OKAY) { goto LBL_T; } /* is it equal to b? */ if (mp_cmp(&t, b) == MP_EQ) { *result = MP_YES; } err = MP_OKAY; LBL_T: mp_clear(&t); return err; } #endif