|
282
|
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, [email protected], http://math.libtomcrypt.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 */ |
|
|
26 int 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; |
|
|
55 LBL_T:mp_clear (&t); |
|
|
56 return err; |
|
|
57 } |
|
|
58 #endif |
