perf(ecdsa): JoinScalarMulBase avoids 0 edge-cases #661
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In ECDSA verification (or ECRecover), we compute
[r/s]pubKey + [h/s]gwhere(r,s)is the signature,hthe hash of the message andgthe canonical generator of the subgroup. Previously, we took into consideration the edge cases where either or bothrandhcan be 0 and alsopubKey=(0,0), but the EYP rules out these:s ≠ 0andr ≠ 0pubKey ≠ (0,0)(because private key≠ 0)The PR introduces the
JointScalarMulBasemethod which performs[s1]p1 + [s2]gassuming thats1ands2are nonzero andp1not the infinity(0,0). This saves ~17k constraints in ECDSA verifier gadget.