/// <summary>Use a special char to padd up to AES block.
/// TODO upgrade the java side
/// Reference:
/// \u2020, ? , a char not easy to be keyed in
/// https://www.unicode.org/charts/PDF/Unicode-3.2/U32-2000.pdf
/// \u0000, Nil
/// https://www.unicode.org/charts/PDF/U0000.pdf
/// </summary>
/// <param name="s"></param>
/// <returns> 16 / 32 byte string
/// </returns>
/// <exception cref="Exception"></exception>
private static byte[] pad16_32(string s)
{
int l = Encoding.Unicode.GetByteCount(s);
if (l <= 16)
{
l = 16;
}
else if (l <= 32)
{
l = 32;
}
else
{
throw new Exception("Not supported block length(16B/32B): " + s);
}
byte[] buf = new byte[l];
LangExt.Fill <byte>(buf, 0);
Encoding.Unicode.GetBytes(s, 0, s.Length, buf, 0);
return(buf);
}