Point at infinity representation in elliptic curve operations

[marcbeep]

Hi, I have a question about the elliptic curve implementation in SecP256.cs.

The code represents the point at infinity as

static BigIntegerPoint ZERO = new BigIntegerPoint(); // Creates (0,0)

However, testing this...

var pointAtInfinity = new BigIntegerPoint();
bool isValid = SecP256.IsOnCurve(pointAtInfinity); // Returns false

For secp256r1, the curve equation is y² = x³ + ax + b where b ≠ 0.
For point (0,0): 0² ≟ 0³ + a(0) + b = b
Since b ≠ 0, point (0,0) should not be considered on the curve.

1. Is this the intended behavior for representing the point at infinity?
2. Could the point.Y == 0 check in Add/Double methods cause issues with legitimate curve points that have Y=0?

I might be missing something. Thanks for maintaining this, let me know how I can help if needed.