Mercurial > dropbear

annotate libtommath/bn_mp_prime_fermat.c @ 1901:4e36e3a95084

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Fix tarball retention-days
author Matt Johnston <matt@ucc.asn.au>
date Thu, 24 Mar 2022 12:26:09 +0800
parents 1051e4eea25a
children
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
Steffen Jaeckel <s_jaeckel@gmx.de>
parents: 1470
diff changeset
1 #include "tommath_private.h"
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2 #ifdef BN_MP_PRIME_FERMAT_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
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4 /* SPDX-License-Identifier: Unlicense */
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6 /* performs one Fermat test.
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7 *
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8 * If "a" were prime then b**a == b (mod a) since the order of
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9 * the multiplicative sub-group would be phi(a) = a-1. That means
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10 * it would be the same as b**(a mod (a-1)) == b**1 == b (mod a).
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11 *
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12 * Sets result to 1 if the congruence holds, or zero otherwise.
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13 */
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14 mp_err mp_prime_fermat(const mp_int *a, const mp_int *b, mp_bool *result)
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15 {
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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16 mp_int t;
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17 mp_err err;
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18
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19 /* default to composite */
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20 *result = MP_NO;
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21
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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22 /* ensure b > 1 */
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23 if (mp_cmp_d(b, 1uL) != MP_GT) {
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24 return MP_VAL;
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25 }
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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27 /* init t */
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28 if ((err = mp_init(&t)) != MP_OKAY) {
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29 return err;
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parents: 1470
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30 }
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31
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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32 /* compute t = b**a mod a */
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33 if ((err = mp_exptmod(b, a, a, &t)) != MP_OKAY) {
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34 goto LBL_T;
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35 }
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1655
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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37 /* is it equal to b? */
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38 if (mp_cmp(&t, b) == MP_EQ) {
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39 *result = MP_YES;
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40 }
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41
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42 err = MP_OKAY;
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43 LBL_T:
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44 mp_clear(&t);
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45 return err;
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46 }
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47 #endif