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