public static FpPoint GetRandomPoint(string input, FpCurve curve, int index, Formatter formater, out int finalCounter)
{
int counter = 0;
ECFieldElement x = null, y = null, z = null;
while (y == null)
{
x = GetX(input, curve, index, counter);
z = x.Multiply(x.Square().Add(curve.A)).Add(curve.B);
if (z.ToBigInteger() == BigInteger.Zero)
{
y = z;
}
else
{
y = z.Sqrt(); // returns null if sqrt does not exist
}
counter++;
}
finalCounter = counter - 1;
if (formater != null)
{
formater.PrintBigInteger("vr_z", "UCAHR", null, z.ToBigInteger());
}
ECFieldElement yPrime = y.Negate();
return(new FpPoint(curve, x, y.ToBigInteger().CompareTo(yPrime.ToBigInteger()) < 0 ? y : yPrime));
}
protected override ECPoint DecompressPoint(int yTilde, BigInteger X1)
{
ECFieldElement eCFieldElement = FromBigInteger(X1);
ECFieldElement eCFieldElement2 = eCFieldElement.Square().Add(A).Multiply(eCFieldElement)
.Add(B);
ECFieldElement eCFieldElement3 = eCFieldElement2.Sqrt();
if (eCFieldElement3 == null)
{
throw new ArgumentException("Invalid point compression");
}
if (eCFieldElement3.TestBitZero() != (yTilde == 1))
{
eCFieldElement3 = eCFieldElement3.Negate();
}
return(CreateRawPoint(eCFieldElement, eCFieldElement3, withCompression: true));
}
protected override ECPoint DecompressPoint(int yTilde, BigInteger X1)
{
ECFieldElement x = FromBigInteger(X1);
ECFieldElement alpha = x.Square().Add(A).Multiply(x).Add(B);
ECFieldElement beta = alpha.Sqrt();
//
// if we can't find a sqrt we haven't got a point on the
// curve - run!
//
if (beta == null)
{
throw new ArithmeticException("Invalid point compression");
}
if (beta.TestBitZero() != (yTilde == 1))
{
// Use the other root
beta = beta.Negate();
}
return(new SecP521R1Point(this, x, beta, true));
}
