fix: elliptic curve subtraction on proper ec points #70
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golang
crypto/ellipticlibrary'sIsOnCurveno longer returns true for ec points with negative values. This is due to the fact that the ec points are defined on[0, P)wherePis the prime order of the field. This leads to a panic when we callcurve.Add()with a point that contains negative values.This wasn't an issue for us since the underlying
curve.Add()operation simply operated on the coordinates of the curve points (addition on x, y coordinates), and we were not using the negative ec point directly, but rather the result of the addition with the negative points, which can be encoded/decoded properly.The fix is to simply modulo the negative value with the curve's underlying field order.