blob: 7b9b12ecf704d44357ea3c3d0218e0da5112e005 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
|
#include <tommath.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.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
*/
/* 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 (mp_int * a, mp_int * b, int *result)
{
mp_int t;
int err;
/* default to composite */
*result = MP_NO;
/* ensure b > 1 */
if (mp_cmp_d(b, 1) != 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
|
