*.encrypted文件结构
(D)
4B: enc data + iv size
16B: iv
{data size}B: enc data(AES256 encryption)


SecretKey = "dB3aqcLtAmBd"
KeyBase = "RWd3NusabzRc"

hmac = new HMACSHA256(Encoding.UTF8.GetBytes(SecretKey))
AESKey = hmac.ComputeHash(Encoding.UTF8.GetBytes(KeyBase))
iv = 看顶上