1 /* $NetBSD: bn_mp_prime_fermat.c,v 1.1.1.2 2014/04/24 12:45:31 pettai Exp $ */
2
3 #include <tommath.h>
4 #ifdef BN_MP_PRIME_FERMAT_C
5 /* LibTomMath, multiple-precision integer library -- Tom St Denis
6 *
7 * LibTomMath is a library that provides multiple-precision
8 * integer arithmetic as well as number theoretic functionality.
9 *
10 * The library was designed directly after the MPI library by
11 * Michael Fromberger but has been written from scratch with
12 * additional optimizations in place.
13 *
14 * The library is free for all purposes without any express
15 * guarantee it works.
16 *
17 * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
18 */
19
20 /* performs one Fermat test.
21 *
22 * If "a" were prime then b**a == b (mod a) since the order of
23 * the multiplicative sub-group would be phi(a) = a-1. That means
24 * it would be the same as b**(a mod (a-1)) == b**1 == b (mod a).
25 *
26 * Sets result to 1 if the congruence holds, or zero otherwise.
27 */
mp_prime_fermat(mp_int * a,mp_int * b,int * result)28 int mp_prime_fermat (mp_int * a, mp_int * b, int *result)
29 {
30 mp_int t;
31 int err;
32
33 /* default to composite */
34 *result = MP_NO;
35
36 /* ensure b > 1 */
37 if (mp_cmp_d(b, 1) != MP_GT) {
38 return MP_VAL;
39 }
40
41 /* init t */
42 if ((err = mp_init (&t)) != MP_OKAY) {
43 return err;
44 }
45
46 /* compute t = b**a mod a */
47 if ((err = mp_exptmod (b, a, a, &t)) != MP_OKAY) {
48 goto LBL_T;
49 }
50
51 /* is it equal to b? */
52 if (mp_cmp (&t, b) == MP_EQ) {
53 *result = MP_YES;
54 }
55
56 err = MP_OKAY;
57 LBL_T:mp_clear (&t);
58 return err;
59 }
60 #endif
61
62 /* Source: /cvs/libtom/libtommath/bn_mp_prime_fermat.c,v */
63 /* Revision: 1.4 */
64 /* Date: 2006/12/28 01:25:13 */
65