加密文件大小的计算与实际大小不匹配

我需要计算使用rijndael加密的文件的大小。

根据本网站和谷歌的其他答案,以下是计算加密数据长度的正确方法:

EL = UL + (BS - (UL Mod BS) Mod BS)

Where: 
EL = Encrypted Length
UL = Unencrypted Length
BS = Block Size

在我的例子中, 未加密的文件长度为5101972字节 ,我正在使用一个128位的加密密钥,给我一个 块大小为16字节 . 因此,方程为:

EL = 5101972 + (16 - (5101972 Mod 16) Mod 16)
EL = 5101972 + (16 - 4 Mod 16)
EL = 5101972 + (12 Mod 16)
EL = 5101972 + 12
EL = 5101984

给予一个 加密文件长度为5101984字节 .

但是,加密后我的文件大小为5242896 140912字节大小的巨大差异!

现在。。显然我做错了什么,但我搞不清是什么。 下面是我的加密和解密测试代码,以及用于计算加密大小的方法:

private static void Enc(string decryptedFileName, string encryptedFileName)
{
    PasswordDeriveBytes passwordDB = new PasswordDeriveBytes("ThisIsMyPassword", Encoding.ASCII.GetBytes("thisIsMysalt!"), "MD5", 2);
    byte[] passwordBytes = passwordDB.GetBytes(128 / 8);

    using (FileStream fsOutput = File.OpenWrite(encryptedFileName))
    {
        using(FileStream fsInput = File.OpenRead(decryptedFileName))
        {
            byte[] IVBytes = Encoding.ASCII.GetBytes("1234567890123456");

            fsOutput.Write(BitConverter.GetBytes(fsInput.Length), 0, 8);
            fsOutput.Write(IVBytes, 0, 16);

            RijndaelManaged symmetricKey = new RijndaelManaged() { Mode = CipherMode.CBC,Padding=PaddingMode.Zeros};
            ICryptoTransform encryptor = symmetricKey.CreateEncryptor(passwordBytes, IVBytes);

            using (CryptoStream cryptoStream = new CryptoStream(fsOutput, encryptor, CryptoStreamMode.Write))
            {
                for (long i = 0; i < fsInput.Length; i += chunkSize)
                {
                    byte[] chunkData = new byte[chunkSize];
                    int bytesRead = 0;
                    while ((bytesRead = fsInput.Read(chunkData, 0, chunkSize)) > 0)
                    {
                        cryptoStream.Write(chunkData, 0, chunkSize);
                    }
                }
            }
        }
    }            
}

private static void Dec(string encryptedFileName, string decryptedFileName)
{
    PasswordDeriveBytes passwordDB = new PasswordDeriveBytes("ThisIsMyPassword", Encoding.ASCII.GetBytes("thisIsMysalt!"), "MD5", 2);
    byte[] passwordBytes = passwordDB.GetBytes(128 / 8);

    using (FileStream fsInput = File.OpenRead(encryptedFileName))
    {
        using (FileStream fsOutput = File.OpenWrite(decryptedFileName))
        {
            byte[] buffer = new byte[8];
            fsInput.Read(buffer, 0, 8);

            long fileLength = BitConverter.ToInt64(buffer, 0);

            byte[] IVBytes = new byte[16];
            fsInput.Read(IVBytes, 0, 16);


            RijndaelManaged symmetricKey = new RijndaelManaged() { Mode = CipherMode.CBC,Padding=PaddingMode.Zeros};
            ICryptoTransform decryptor = symmetricKey.CreateDecryptor(passwordBytes, IVBytes);

            using (CryptoStream cryptoStream = new CryptoStream(fsOutput, decryptor, CryptoStreamMode.Write))
            {
                for (long i = 0; i < fsInput.Length; i += chunkSize)
                {
                    byte[] chunkData = new byte[chunkSize];
                    int bytesRead = 0;
                    while ((bytesRead = fsInput.Read(chunkData, 0, chunkSize)) > 0)
                    {
                        cryptoStream.Write(chunkData, 0, bytesRead);
                    }
                }
                fsOutput.SetLength(fileLength);
            }                    
        }
    }
}

private static void CalcEncSize(string decryptedFileName)
{
    FileInfo fi = new FileInfo(decryptedFileName);
    if (fi.Exists)
    {                
        long blockSize = 128/8;
        long fileLength = fi.Length;
        long encryptedSize = fileLength + ((blockSize - (fileLength % blockSize)) % blockSize);
        encryptedSize += 24; //16 bytes for the IV, and 8 more for the filelength, both stored at the start of the file.

        Console.WriteLine("Estimated Encryption Size: " + encryptedSize.ToString());           
    }
}

注:在开始的计算中,我不包括在加密文件开始时自己用来存储原始文件长度的额外24个字节,以及IV…我知道这一点,但不想把方程复杂化。