private static void EncodePoint(PointExt p, byte[] r, int rOff)
{
uint[] x = X448Field.Create();
uint[] y = X448Field.Create();
X448Field.Inv(p.z, y);
X448Field.Mul(p.x, y, x);
X448Field.Mul(p.y, y, y);
X448Field.Normalize(x);
X448Field.Normalize(y);
X448Field.Encode(y, r, rOff);
r[rOff + PointBytes - 1] = (byte)((x[0] & 1) << 7);
}
private static int CheckPoint(uint[] x, uint[] y)
{
uint[] t = X448Field.Create();
uint[] u = X448Field.Create();
uint[] v = X448Field.Create();
X448Field.Sqr(x, u);
X448Field.Sqr(y, v);
X448Field.Mul(u, v, t);
X448Field.Add(u, v, u);
X448Field.Mul(t, -C_d, t);
X448Field.SubOne(t);
X448Field.Add(t, u, t);
X448Field.Normalize(t);
return(X448Field.IsZero(t));
}
private static bool DecodePointVar(byte[] p, int pOff, bool negate, PointExt r)
{
byte[] py = Arrays.CopyOfRange(p, pOff, pOff + PointBytes);
if (!CheckPointVar(py))
{
return(false);
}
int x_0 = (py[PointBytes - 1] & 0x80) >> 7;
py[PointBytes - 1] &= 0x7F;
X448Field.Decode(py, 0, r.y);
uint[] u = X448Field.Create();
uint[] v = X448Field.Create();
X448Field.Sqr(r.y, u);
X448Field.Mul(u, (uint)-C_d, v);
X448Field.Negate(u, u);
X448Field.AddOne(u);
X448Field.AddOne(v);
if (!X448Field.SqrtRatioVar(u, v, r.x))
{
return(false);
}
X448Field.Normalize(r.x);
if (x_0 == 1 && X448Field.IsZeroVar(r.x))
{
return(false);
}
if (negate ^ (x_0 != (r.x[0] & 1)))
{
X448Field.Negate(r.x, r.x);
}
PointExtendXY(r);
return(true);
}