## File: bn_mp_prime_fermat.c

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libtommath 1.1.0-3
 `123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960` ``````#include "tommath_private.h" #ifdef BN_MP_PRIME_FERMAT_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * 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. */ int mp_prime_fermat(const mp_int *a, const mp_int *b, int *result) { mp_int t; int 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 /* ref: HEAD -> master, tag: v1.1.0 */ /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */ /* commit time: 2019-01-28 20:32:32 +0100 */ ``````