Mercurial > dropbear

annotate libtommath/bn_mp_prime_fermat.c @ 447:278805938dcf

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Patch from Nicolai Ehemann to try binding before going to the background, so that if it exits early (because something's already listening etc) then it will return an exitcode of 1.
author Matt Johnston <matt@ucc.asn.au>
date Thu, 19 Jul 2007 15:54:18 +0000
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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38
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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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48
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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 $ */