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Small primes are primes too.

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Previously, BN_is_prime_fasttest_ex, when doing trial-division, would
check whether the candidate is a multiple of a number of small primes
and, if so, reject it. However, three is a multiple of three yet is
still a prime number.

This change accepts small primes as prime when doing trial-division.

Reviewed-by: Kurt Roeckx <kurt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3264)
This commit is contained in:
Adam Langley 2017-04-20 09:20:50 -07:00 committed by Rich Salz
parent c0452248ea
commit 6e64c56066
2 changed files with 25 additions and 1 deletions
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2
crypto/bn/bn_prime.c
View File

@ -176,7 +176,7 @@ int BN_is_prime_fasttest_ex(const BIGNUM *a, int checks, BN_CTX *ctx_passed,
if (mod == (BN_ULONG)-1)
goto err;
if (mod == 0)
return 0;
return BN_is_word(a, primes[i]);
}
if (!BN_GENCB_call(cb, 1, -1))
goto err;

24
test/bntest.c
View File

@ -2084,6 +2084,29 @@ err:
return st;
}
static int test_3_is_prime()
{
int ret = 0;
BIGNUM *r = BN_new();
/* For a long time, small primes were not considered prime when
* do_trial_division was set. */
if (r == NULL ||
!BN_set_word(r, 3) ||
BN_is_prime_fasttest_ex(r, 3 /* nchecks */, ctx,
0 /* do_trial_division */, NULL) != 1 ||
BN_is_prime_fasttest_ex(r, 3 /* nchecks */, ctx,
1 /* do_trial_division */, NULL) != 1) {
goto err;
}
ret = 1;
err:
BN_free(r);
return ret;
}
/* Delete leading and trailing spaces from a string */
static char *strip_spaces(char *p)
@ -2250,6 +2273,7 @@ int test_main(int argc, char *argv[])
ADD_TEST(test_gf2m_modsqrt);
ADD_TEST(test_gf2m_modsolvequad);
#endif
ADD_TEST(test_3_is_prime);
ADD_TEST(file_tests);
RAND_seed(rnd_seed, sizeof rnd_seed);