private BigInteger Sqrt(BigInteger x, AnyRng rng)
{
if (!IsQuadraticResidue(x))
{
throw new InvalidOperationException();
}
BigInteger z;
do
{
z = rng.NextBigInt(BigInteger.One, P);
} while (IsQuadraticResidue(z));
var q = _eulerPower;
ulong s = 1;
while (q.IsEven)
{
s++;
q /= 2;
}
var m = s;
var c = BigInteger.ModPow(z, q, P);
var t = BigInteger.ModPow(x, q, P);
var r = BigInteger.ModPow(x, q / 2 + 1, P);
while (true)
{
if (t.IsZero)
{
return(BigInteger.Zero);
}
if (t.IsOne)
{
return(r);
}
ulong i = 1;
while (i < m)
{
if (BigInteger.ModPow(t, BigInteger.ModPow(2, i, P), P).IsOne)
{
break;
}
i++;
}
if (i == m)
{
throw new InvalidOperationException();
}
var b = BigInteger.ModPow(c, BigInteger.ModPow(2, m - i - 1, P), P);
m = i;
c = b * b % P;
t = t * b * b % P;
r = r * b % P;
}
}
public JacobianEcPoint Multiply(BigInteger k, JacobianEcPoint p, AnyRng rng)
{
if (k.Sign < 0)
{
k = -k;
p = Negate(p);
}
if (k.IsZero)
{
return(JacobianEcPoint.Infinity);
}
if (k.IsOne)
{
return(p);
}
var ks = rng.NextBigInt(BigInteger.One, k);
// return MultiplyAndAdd(ks, p, k - ks, p, rng);
var(k1, k2) = ToNafBytes(k - ks, ks);
var i = 0;
while (i < k1.Length - 1)
{
var c = k1[i].NafValue() + k2[i].NafValue();
if (c != 0)
{
i++;
continue;
}
if (k2[i + 1].NafValue() > 0)
{
k2[i + 1] = (byte)((k2[i + 1].H() << 4) | ((k2[i + 1].L() - 1) & 0xF));
k2[i] = (byte)(((k2[i].H() + 2) << 4) | (k2[i].L() & 0xF));
}
else
{
k2[i + 1] = (byte)((k2[i + 1].H() << 4) | ((k2[i + 1].L() + 1) & 0xF));
k2[i] = (byte)(((k2[i].H() - 2) << 4) | (k2[i].L() & 0xF));
}
}
var lut = new [] {
JacobianEcPoint.Infinity,
p,
Double(p),
Add(Double(p), p),
Double(Double(p))
};
var r = lut[k1.Back().NafValue() + k2.Back().NafValue()];
for (i = k1.Length - 2; i >= 0; i--)
{
var c = k1[i].NafValue() + k2[i].NafValue();
r = Add(Double(Double(r)), c < 0 ? Negate(lut[-c]) : lut[c]);
}
return(r);
}
