Replace GF(256) division with a constant time impl #9932
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sgmiller
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briankassouf
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briankassouf
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WIP, according to the issue, mul isn't constant time either. Need to look more closely at that side. |
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Okay, mul/div/invert all good to go. |
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The implementation of division in the finite field GF(2^8) used by the shamir code had a test in order to correct modulo division on a uint8 that made it not constant time, as well as intermediate assignments that the Go compiler was optimizing away.
This removes the conditional modulo in div() and replaces the assignments and branches with ConstantTimeSelects.
Addresses ToB-004.