public bool TryFindY(BigInteger x, byte firstByte, out BigInteger y)
{
if (firstByte != 2 && firstByte != 3)
{
y = 0;
return(false);
}
if (x.Sign < 1)
{
y = 0;
return(false);
}
// y2 = x3 + ax + b (mod p)
BigInteger right = (BigInteger.Pow(x, 3) + BigInteger.Multiply(curve.A, x) + curve.B) % curve.P;
try
{
y = SquareRoot.FindSquareRoot(right, curve.P);
}
catch (ArithmeticException)
{
y = 0;
return(false);
}
if (firstByte == 2 && !y.IsEven)
{
y = PointNegChecked(new EllipticCurvePoint(x, y)).Y;
return(true);
}
else if (firstByte == 3 && y.IsEven)
{
y = PointNegChecked(new EllipticCurvePoint(x, y)).Y;
return(true);
}
else
{
return(true);
}
}