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comparison libtommath/bn_mp_prime_fermat.c @ 1739:13d834efc376 fuzz

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merge from main
author Matt Johnston <matt@ucc.asn.au>
date Thu, 15 Oct 2020 19:55:15 +0800
parents 1051e4eea25a
children
comparison
equal deleted inserted replaced
1562:768ebf737aa0 1739:13d834efc376
1 #include <tommath_private.h> 1 #include "tommath_private.h"
2 #ifdef BN_MP_PRIME_FERMAT_C 2 #ifdef BN_MP_PRIME_FERMAT_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
4 * 4 /* SPDX-License-Identifier: Unlicense */
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://libtom.org
16 */
17 5
18 /* performs one Fermat test. 6 /* performs one Fermat test.
19 * 7 *
20 * If "a" were prime then b**a == b (mod a) since the order of 8 * 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 9 * 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). 10 * it would be the same as b**(a mod (a-1)) == b**1 == b (mod a).
23 * 11 *
24 * Sets result to 1 if the congruence holds, or zero otherwise. 12 * Sets result to 1 if the congruence holds, or zero otherwise.
25 */ 13 */
26 int mp_prime_fermat (mp_int * a, mp_int * b, int *result) 14 mp_err mp_prime_fermat(const mp_int *a, const mp_int *b, mp_bool *result)
27 { 15 {
28 mp_int t; 16 mp_int t;
29 int err; 17 mp_err err;
30 18
31 /* default to composite */ 19 /* default to composite */
32 *result = MP_NO; 20 *result = MP_NO;
33 21
34 /* ensure b > 1 */ 22 /* ensure b > 1 */
35 if (mp_cmp_d(b, 1) != MP_GT) { 23 if (mp_cmp_d(b, 1uL) != MP_GT) {
36 return MP_VAL; 24 return MP_VAL;
37 } 25 }
38 26
39 /* init t */ 27 /* init t */
40 if ((err = mp_init (&t)) != MP_OKAY) { 28 if ((err = mp_init(&t)) != MP_OKAY) {
41 return err; 29 return err;
42 } 30 }
43 31
44 /* compute t = b**a mod a */ 32 /* compute t = b**a mod a */
45 if ((err = mp_exptmod (b, a, a, &t)) != MP_OKAY) { 33 if ((err = mp_exptmod(b, a, a, &t)) != MP_OKAY) {
46 goto LBL_T; 34 goto LBL_T;
47 } 35 }
48 36
49 /* is it equal to b? */ 37 /* is it equal to b? */
50 if (mp_cmp (&t, b) == MP_EQ) { 38 if (mp_cmp(&t, b) == MP_EQ) {
51 *result = MP_YES; 39 *result = MP_YES;
52 } 40 }
53 41
54 err = MP_OKAY; 42 err = MP_OKAY;
55 LBL_T:mp_clear (&t); 43 LBL_T:
56 return err; 44 mp_clear(&t);
45 return err;
57 } 46 }
58 #endif 47 #endif
59
60 /* ref: $Format:%D$ */
61 /* git commit: $Format:%H$ */
62 /* commit time: $Format:%ai$ */