public EllipticCurvePoint Twice(EllipticCurvePoint a)
{
if (EllipticCurvePoint.IsInfinity(a))
{
return(a);
}
BigInteger sigma = a.X.InverseGF(curve.P).MultGF(a.Y, curve.P).AddGF(a.X);
BigInteger x = sigma.SquareGF(curve.P).AddGF(sigma).AddGF(curve.A);
BigInteger y = a.X.SquareGF(curve.P).AddGF(sigma.AddGF(BigInteger.One).MultGF(x, curve.P));
var result = new EllipticCurvePoint(x, y);
//CheckOnCurve(result);
return(result);
}
public static BigInteger InverseGF(this BigInteger value, BigInteger modulus)
{
BigInteger b = 1, c = 0, u = value, v = modulus;
while (u.GetBitCount() > 1)
{
int j = u.GetBitCount() - v.GetBitCount();
if (j < 0)
{
(u, v) = (v, u);
(c, b) = (b, c);
j = -j;
}
u = u.AddGF(v << j);
b = b.AddGF(c << j);
}
return(b);
}
