Constant-time divisors #617
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x**3 / (0 y + x**1) would prior be considered indivisible with iterations = 0. It is divisible however. The amount of iterations should be the amount of coefficients within the numerator *excluding the coefficient for y**0 x**0*.
…quivalence If the first passed argument is smaller than the latter, it's padded to the necessary length. Also adds code to trim the remainder as the remainder is the value modulo, so it's very important it remains concise and workable.
It selected the case if both were identity before selecting the case if either were identity, the latter overwriting the former.
1) Our quotient structure does need to be of size equal to the numerator entirely to prevent out-of-bounds reads on it 2) We need to get from yx_coefficients if of length >=, so if the length is 1 we can read y_pow=1 from it. If y_pow=0, and its length is 0 so it has no inner Vecs, we need to fall back with the guard y_pow != 0.
…bly gigantic Our Poly algorithm is incredibly leaky. While it presumably should be improved, we can take advantage of our known structure while constructing divisors (and the small modulus) to simply trim out the zero coefficients leaked. This maintains Polys in a manageable size.
…divisors Anyone creating a divisor for the scalar mul gadget should use constant time code, so this code should at least be in the EC gadgets crate It's of non-trivial complexity to deal with otherwise.
kayabaNerve
added
improvement
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Thanks to @Boog900 for reviewing my initial ct_* functions and helping improve then to what they are now. |
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This is 9.6x slower yet ensures timing analysis of the divisor calculation doesn't leak any information about the secret key.