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Allow small RSA exponents in the default provider

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Fixes #16255

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16285)
This commit is contained in:
Shane Lontis 2021-08-11 12:23:08 +10:00 committed by Tomas Mraz
parent a5f4099d27
commit 254957f768
2 changed files with 18 additions and 24 deletions
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27
crypto/rsa/rsa_sp800_56b_check.c
View File

@ -218,30 +218,21 @@ int ossl_rsa_check_private_exponent(const RSA *rsa, int nbits, BN_CTX *ctx)
return ret;
}
#ifndef FIPS_MODULE
static int bn_is_three(const BIGNUM *bn)
{
BIGNUM *num = BN_dup(bn);
int ret = (num != NULL && BN_sub_word(num, 3) && BN_is_zero(num));
BN_free(num);
return ret;
}
#endif /* FIPS_MODULE */
/* Check exponent is odd, and has a bitlen ranging from [17..256] */
/*
* Check exponent is odd.
* For FIPS also check the bit length is in the range [17..256]
*/
int ossl_rsa_check_public_exponent(const BIGNUM *e)
{
#ifdef FIPS_MODULE
int bitlen;
/* For legacy purposes RSA_3 is allowed in non fips mode */
#ifndef FIPS_MODULE
if (bn_is_three(e))
return 1;
#endif /* FIPS_MODULE */
bitlen = BN_num_bits(e);
return (BN_is_odd(e) && bitlen > 16 && bitlen < 257);
#else
/* Allow small exponents larger than 1 for legacy purposes */
return BN_is_odd(e) && BN_cmp(e, BN_value_one()) > 0;
#endif /* FIPS_MODULE */
}
/*

15
test/rsa_sp800_56b_test.c
View File

@ -104,26 +104,29 @@ static BIGNUM *bn_load_new(const unsigned char *data, int sz)
return ret;
}
/* Check that small rsa exponents are allowed in non FIPS mode */
static int test_check_public_exponent(void)
{
int ret = 0;
BIGNUM *e = NULL;
ret = TEST_ptr(e = BN_new())
/* e is too small */
&& TEST_true(BN_set_word(e, 65535))
/* e is too small will fail */
&& TEST_true(BN_set_word(e, 1))
&& TEST_false(ossl_rsa_check_public_exponent(e))
/* e is even will fail */
&& TEST_true(BN_set_word(e, 65536))
&& TEST_false(ossl_rsa_check_public_exponent(e))
/* e is ok */
&& TEST_true(BN_set_word(e, 3))
&& TEST_true(ossl_rsa_check_public_exponent(e))
&& TEST_true(BN_set_word(e, 17))
&& TEST_true(ossl_rsa_check_public_exponent(e))
&& TEST_true(BN_set_word(e, 65537))
&& TEST_true(ossl_rsa_check_public_exponent(e))
/* e = 2^256 is too big */
/* e = 2^256 + 1 is ok */
&& TEST_true(BN_lshift(e, BN_value_one(), 256))
&& TEST_false(ossl_rsa_check_public_exponent(e))
/* e = 2^256-1 is odd and in range */
&& TEST_true(BN_sub(e, e, BN_value_one()))
&& TEST_true(BN_add(e, e, BN_value_one()))
&& TEST_true(ossl_rsa_check_public_exponent(e));
BN_free(e);
return ret;