Mercurial > dropbear

annotate libtommath/bn_mp_prime_fermat.c @ 1156:a8f4dade70e5

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avoid getpass when not used some systems (like android's bionic) do not provide getpass. you can disable ENABLE_CLI_PASSWORD_AUTH & ENABLE_CLI_INTERACT_AUTH to avoid its use (and rely on pubkey auth), but the link still fails because the support file calls getpass. do not define this func if both of those auth methods are not used.
author Mike Frysinger <vapier@gentoo.org>
date Wed, 21 Oct 2015 22:39:55 +0800
parents 5ff8218bcee9
children 60fc6476e044
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1 #include <tommath.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 *
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5 * LibTomMath is a library that provides multiple-precision
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6 * integer arithmetic as well as number theoretic functionality.
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7 *
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8 * The library was designed directly after the MPI library by
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9 * Michael Fromberger but has been written from scratch with
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10 * additional optimizations in place.
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11 *
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12 * The library is free for all purposes without any express
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13 * guarantee it works.
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14 *
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.com
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16 */
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17
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18 /* performs one Fermat test.
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19 *
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20 * If "a" were prime then b**a == b (mod a) since the order of
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21 * the multiplicative sub-group would be phi(a) = a-1. That means
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22 * it would be the same as b**(a mod (a-1)) == b**1 == b (mod a).
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23 *
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24 * Sets result to 1 if the congruence holds, or zero otherwise.
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25 */
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26 int mp_prime_fermat (mp_int * a, mp_int * b, int *result)
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27 {
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28 mp_int t;
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29 int err;
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30
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31 /* default to composite */
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32 *result = MP_NO;
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33
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34 /* ensure b > 1 */
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35 if (mp_cmp_d(b, 1) != MP_GT) {
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36 return MP_VAL;
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37 }
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39 /* init t */
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40 if ((err = mp_init (&t)) != MP_OKAY) {
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41 return err;
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42 }
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44 /* compute t = b**a mod a */
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45 if ((err = mp_exptmod (b, a, a, &t)) != MP_OKAY) {
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46 goto LBL_T;
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47 }
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49 /* is it equal to b? */
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50 if (mp_cmp (&t, b) == MP_EQ) {
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51 *result = MP_YES;
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52 }
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53
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54 err = MP_OKAY;
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55 LBL_T:mp_clear (&t);
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56 return err;
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57 }
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58 #endif
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59
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60 /* $Source: /cvs/libtom/libtommath/bn_mp_prime_fermat.c,v $ */
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61 /* $Revision: 1.3 $ */
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62 /* $Date: 2006/03/31 14:18:44 $ */