kaidokert / krabiecdsa-rs / 31327529029

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Coordinate-randomization blinding for the randomized signer (#37)

* Coordinate-randomization blinding for the randomized signer

The randomized signer's scalar multiply ran on the same projective
coordinates every signature, leaving the point arithmetic open to
DPA/CPA trace averaging. RandomizedSigningKey now draws a random field
element λ alongside the RFC 6979 §3.6 hedge entropy and scales the base
point (X:Y:Z) → (λX:λY:λZ). The affine result x(k·G) = X/Z is unchanged,
so the signature is bit-identical, but every ladder trace now runs on
different field values.

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