42 lines
960 B
C
42 lines
960 B
C
|
#include "tommath_private.h"
|
||
|
|
#ifdef 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, bool *result)
|
||
|
|
{
|
||
|
|
mp_int t;
|
||
|
|
mp_err err;
|
||
|
|
|
||
|
|
/* 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_ERR;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* is it equal to b? */
|
||
|
|
*result = mp_cmp(&t, b) == MP_EQ;
|
||
|
|
|
||
|
|
LBL_ERR:
|
||
|
|
mp_clear(&t);
|
||
|
|
return err;
|
||
|
|
}
|
||
|
|
#endif
|