Mercurial > dropbear
view libtommath/bn_mp_prime_miller_rabin.c @ 397:2908122e9eed channel-fix
disapproval of revision '1250b8af44b62d8f4fe0f8d9fc7e7a1cc34e7e1c'
author | Matt Johnston <matt@ucc.asn.au> |
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date | Sat, 03 Feb 2007 08:10:09 +0000 (2007-02-03) |
parents | eed26cff980b |
children | 5ff8218bcee9 |
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#include <tommath.h> #ifdef BN_MP_PRIME_MILLER_RABIN_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org */ /* Miller-Rabin test of "a" to the base of "b" as described in * HAC pp. 139 Algorithm 4.24 * * Sets result to 0 if definitely composite or 1 if probably prime. * Randomly the chance of error is no more than 1/4 and often * very much lower. */ int mp_prime_miller_rabin (mp_int * a, mp_int * b, int *result) { mp_int n1, y, r; int s, j, err; /* default */ *result = MP_NO; /* ensure b > 1 */ if (mp_cmp_d(b, 1) != MP_GT) { return MP_VAL; } /* get n1 = a - 1 */ if ((err = mp_init_copy (&n1, a)) != MP_OKAY) { return err; } if ((err = mp_sub_d (&n1, 1, &n1)) != MP_OKAY) { goto LBL_N1; } /* set 2**s * r = n1 */ if ((err = mp_init_copy (&r, &n1)) != MP_OKAY) { goto LBL_N1; } /* count the number of least significant bits * which are zero */ s = mp_cnt_lsb(&r); /* now divide n - 1 by 2**s */ if ((err = mp_div_2d (&r, s, &r, NULL)) != MP_OKAY) { goto LBL_R; } /* compute y = b**r mod a */ if ((err = mp_init (&y)) != MP_OKAY) { goto LBL_R; } if ((err = mp_exptmod (b, &r, a, &y)) != MP_OKAY) { goto LBL_Y; } /* if y != 1 and y != n1 do */ if (mp_cmp_d (&y, 1) != MP_EQ && mp_cmp (&y, &n1) != MP_EQ) { j = 1; /* while j <= s-1 and y != n1 */ while ((j <= (s - 1)) && mp_cmp (&y, &n1) != MP_EQ) { if ((err = mp_sqrmod (&y, a, &y)) != MP_OKAY) { goto LBL_Y; } /* if y == 1 then composite */ if (mp_cmp_d (&y, 1) == MP_EQ) { goto LBL_Y; } ++j; } /* if y != n1 then composite */ if (mp_cmp (&y, &n1) != MP_EQ) { goto LBL_Y; } } /* probably prime now */ *result = MP_YES; LBL_Y:mp_clear (&y); LBL_R:mp_clear (&r); LBL_N1:mp_clear (&n1); return err; } #endif