Mercurial > dropbear
annotate bn_mp_prime_miller_rabin.c @ 203:e109027b9edf libtommath LTM_DB_0.46 LTM_DB_0.47
Don't remove ~ files on make clean (and find -type was wrong anyway)
| author | Matt Johnston <matt@ucc.asn.au> |
|---|---|
| date | Wed, 11 May 2005 16:27:28 +0000 |
| parents | d8254fc979e9 |
| children |
| rev | line source |
|---|---|
| 142 | 1 #include <tommath.h> |
| 2 #ifdef BN_MP_PRIME_MILLER_RABIN_C | |
| 2 | 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis |
| 4 * | |
| 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://math.libtomcrypt.org | |
| 16 */ | |
| 17 | |
| 18 /* Miller-Rabin test of "a" to the base of "b" as described in | |
| 19 * HAC pp. 139 Algorithm 4.24 | |
| 20 * | |
| 21 * Sets result to 0 if definitely composite or 1 if probably prime. | |
| 22 * Randomly the chance of error is no more than 1/4 and often | |
| 23 * very much lower. | |
| 24 */ | |
| 25 int mp_prime_miller_rabin (mp_int * a, mp_int * b, int *result) | |
| 26 { | |
| 27 mp_int n1, y, r; | |
| 28 int s, j, err; | |
| 29 | |
| 30 /* default */ | |
| 31 *result = MP_NO; | |
| 32 | |
| 33 /* ensure b > 1 */ | |
| 34 if (mp_cmp_d(b, 1) != MP_GT) { | |
| 35 return MP_VAL; | |
| 36 } | |
| 37 | |
| 38 /* get n1 = a - 1 */ | |
| 39 if ((err = mp_init_copy (&n1, a)) != MP_OKAY) { | |
| 40 return err; | |
| 41 } | |
| 42 if ((err = mp_sub_d (&n1, 1, &n1)) != MP_OKAY) { | |
|
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43 goto LBL_N1; |
| 2 | 44 } |
| 45 | |
| 46 /* set 2**s * r = n1 */ | |
| 47 if ((err = mp_init_copy (&r, &n1)) != MP_OKAY) { | |
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48 goto LBL_N1; |
| 2 | 49 } |
| 50 | |
| 51 /* count the number of least significant bits | |
| 52 * which are zero | |
| 53 */ | |
| 54 s = mp_cnt_lsb(&r); | |
| 55 | |
| 56 /* now divide n - 1 by 2**s */ | |
| 57 if ((err = mp_div_2d (&r, s, &r, NULL)) != MP_OKAY) { | |
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58 goto LBL_R; |
| 2 | 59 } |
| 60 | |
| 61 /* compute y = b**r mod a */ | |
| 62 if ((err = mp_init (&y)) != MP_OKAY) { | |
|
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63 goto LBL_R; |
| 2 | 64 } |
| 65 if ((err = mp_exptmod (b, &r, a, &y)) != MP_OKAY) { | |
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66 goto LBL_Y; |
| 2 | 67 } |
| 68 | |
| 69 /* if y != 1 and y != n1 do */ | |
| 70 if (mp_cmp_d (&y, 1) != MP_EQ && mp_cmp (&y, &n1) != MP_EQ) { | |
| 71 j = 1; | |
| 72 /* while j <= s-1 and y != n1 */ | |
| 73 while ((j <= (s - 1)) && mp_cmp (&y, &n1) != MP_EQ) { | |
| 74 if ((err = mp_sqrmod (&y, a, &y)) != MP_OKAY) { | |
|
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75 goto LBL_Y; |
| 2 | 76 } |
| 77 | |
| 78 /* if y == 1 then composite */ | |
| 79 if (mp_cmp_d (&y, 1) == MP_EQ) { | |
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80 goto LBL_Y; |
| 2 | 81 } |
| 82 | |
| 83 ++j; | |
| 84 } | |
| 85 | |
| 86 /* if y != n1 then composite */ | |
| 87 if (mp_cmp (&y, &n1) != MP_EQ) { | |
|
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88 goto LBL_Y; |
| 2 | 89 } |
| 90 } | |
| 91 | |
| 92 /* probably prime now */ | |
| 93 *result = MP_YES; | |
|
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94 LBL_Y:mp_clear (&y); |
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95 LBL_R:mp_clear (&r); |
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96 LBL_N1:mp_clear (&n1); |
| 2 | 97 return err; |
| 98 } | |
| 142 | 99 #endif |