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Prime-related bugfixes (#81)

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* Merge pull request #180 from czurnieden/isprimeerror

Fixed bug in mp_prime_isprime
(cherry picked from commit f3ff7064f3301a2fc11b84d389fd67769862d437)

* do 2 MR rounds for numbers >=2048bits

* back-port modified mp_prime_next_prime()
This commit is contained in:
Steffen Jaeckel 2019-09-17 16:11:09 +02:00 committed by Matt Johnston
parent 615ed4e46a
commit c71258625d
3 changed files with 18 additions and 34 deletions
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7
libtommath/bn_mp_prime_is_prime.c
View File

@ -332,16 +332,15 @@ int mp_prime_is_prime(const mp_int *a, int t, int *result)
} }
/* /*
* That number might got too big and the witness has to be * That number might got too big and the witness has to be
* smaller than or equal to "a" * smaller than "a"
*/ */
len = mp_count_bits(&b); len = mp_count_bits(&b);
if (len > size_a) { if (len >= size_a) {
len = len - size_a; len = (len - size_a) + 1;
if ((err = mp_div_2d(&b, len, &b, NULL)) != MP_OKAY) { if ((err = mp_div_2d(&b, len, &b, NULL)) != MP_OKAY) {
goto LBL_B; goto LBL_B;
} }
} }
/* Although the chance for b <= 3 is miniscule, try again. */ /* Although the chance for b <= 3 is miniscule, try again. */
if (mp_cmp_d(&b, 3uL) != MP_GT) { if (mp_cmp_d(&b, 3uL) != MP_GT) {
ix--; ix--;

40
libtommath/bn_mp_prime_next_prime.c
View File

@ -19,7 +19,7 @@
*/ */
int mp_prime_next_prime(mp_int *a, int t, int bbs_style) int mp_prime_next_prime(mp_int *a, int t, int bbs_style)
{ {
int err, res = MP_NO, x, y; int err, res = MP_NO, x, y, cmp;
mp_digit res_tab[PRIME_SIZE], step, kstep; mp_digit res_tab[PRIME_SIZE], step, kstep;
mp_int b; mp_int b;
@ -28,36 +28,22 @@ int mp_prime_next_prime(mp_int *a, int t, int bbs_style)
/* simple algo if a is less than the largest prime in the table */ /* simple algo if a is less than the largest prime in the table */
if (mp_cmp_d(a, ltm_prime_tab[PRIME_SIZE-1]) == MP_LT) { if (mp_cmp_d(a, ltm_prime_tab[PRIME_SIZE-1]) == MP_LT) {
/* find which prime it is bigger than */ /* find which prime it is bigger than "a" */
for (x = PRIME_SIZE - 2; x >= 0; x--) { for (x = 0; x < PRIME_SIZE; x++) {
if (mp_cmp_d(a, ltm_prime_tab[x]) != MP_LT) { cmp = mp_cmp_d(a, ltm_prime_tab[x]);
if (bbs_style == 1) { if (cmp == MP_EQ) {
/* ok we found a prime smaller or continue;
* equal [so the next is larger] }
* if (cmp != MP_GT) {
* however, the prime must be if ((bbs_style == 1) && ((ltm_prime_tab[x] & 3u) != 3u)) {
* congruent to 3 mod 4 /* try again until we get a prime congruent to 3 mod 4 */
*/ continue;
if ((ltm_prime_tab[x + 1] & 3u) != 3u) {
/* scan upwards for a prime congruent to 3 mod 4 */
for (y = x + 1; y < PRIME_SIZE; y++) {
if ((ltm_prime_tab[y] & 3u) == 3u) {
mp_set(a, ltm_prime_tab[y]);
return MP_OKAY;
}
}
}
} else { } else {
mp_set(a, ltm_prime_tab[x + 1]); mp_set(a, ltm_prime_tab[x]);
return MP_OKAY; return MP_OKAY;
} }
} }
} }
/* at this point a maybe 1 */
if (mp_cmp_d(a, 1uL) == MP_EQ) {
mp_set(a, 2uL);
return MP_OKAY;
}
/* fall through to the sieve */ /* fall through to the sieve */
} }
@ -75,7 +61,7 @@ int mp_prime_next_prime(mp_int *a, int t, int bbs_style)
if ((a->dp[0] & 3u) != 3u) { if ((a->dp[0] & 3u) != 3u) {
if ((err = mp_sub_d(a, (a->dp[0] & 3u) + 1u, a)) != MP_OKAY) { if ((err = mp_sub_d(a, (a->dp[0] & 3u) + 1u, a)) != MP_OKAY) {
return err; return err;
}; }
} }
} else { } else {
if (mp_iseven(a) == MP_YES) { if (mp_iseven(a) == MP_YES) {

5
libtommath/bn_mp_prime_rabin_miller_trials.c
View File

@ -29,8 +29,7 @@ static const struct {
{ 768, 5 }, { 768, 5 },
{ 896, 4 }, { 896, 4 },
{ 1024, 4 }, { 1024, 4 },
{ 2048, 2 }, { 2048, 2 } /* For bigger keysizes use always at least 2 Rounds */
{ 4096, 1 },
}; };
/* returns # of RM trials required for a given bit size and max. error of 2^(-96)*/ /* returns # of RM trials required for a given bit size and max. error of 2^(-96)*/
@ -45,7 +44,7 @@ int mp_prime_rabin_miller_trials(int size)
return (x == 0) ? sizes[0].t : sizes[x - 1].t; return (x == 0) ? sizes[0].t : sizes[x - 1].t;
} }
} }
return sizes[x-1].t + 1; return sizes[x-1].t;
} }