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Handle edge cases with MP_8BIT and use correct upper limit for the random witnesses

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czurnieden 2018-05-14 03:46:24 +02:00 committed by Steffen Jaeckel
parent ba786e6b39
commit 38e8f93bdb
1 changed files with 26 additions and 2 deletions
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28
bn_mp_prime_is_prime.c
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@ -70,6 +70,12 @@ int mp_prime_is_prime(const mp_int *a, int t, int *result)
return MP_OKAY;
}
}
#ifdef MP_8BIT
// The search in the loop above was exhaustive in this case
if (a->used == 1 && PRIME_SIZE >= 31) {
return MP_OKAY;
}
#endif
/* first perform trial division */
if ((err = mp_prime_is_divisible(a, &res)) != MP_OKAY) {
@ -276,21 +282,39 @@ int mp_prime_is_prime(const mp_int *a, int t, int *result)
}
fips_rand <<= sizeof(mp_digit) * CHAR_BIT;
fips_rand |= (unsigned int) b.dp[0];
fips_rand &= mask;
}
#endif
// Ceil, because small numbers have a right to live, too,
len = (int) ( ((fips_rand & mask) + DIGIT_BIT) / DIGIT_BIT);
len = (int) ( (fips_rand + DIGIT_BIT) / DIGIT_BIT);
// Unlikely.
if(len < 0){
ix--;
continue;
}
// As mentioned above, one 8-bit digit is too small and
// although it can only happen in the unlikely case that
// an "unsigned int" is smaller than 16 bit a simple test
// is cheap and the correction even cheaper.
#ifdef MP_8BIT
// All "a" < 2^8 have been caught before
if(len == 1){
len++;
}
#endif
if ((err = mp_rand(&b, len)) != MP_OKAY) {
goto LBL_B;
}
// That number might got too big and the witness has to be
// smaller than or equal to "a"
len = mp_count_bits(&b);
if (len > size_a) {
len = len - size_a;
mp_div_2d(&b, len, &b, NULL);
}
// Although the chance for b <= 3 is miniscule, try again.
if(mp_cmp_d(&b,3) != MP_GT) {
if (mp_cmp_d(&b,3) != MP_GT) {
ix--;
continue;
}