逐行加密/解密文件？

我是加密的新手，我正在努力让逐行加密器工作;我需要能够在应用程序运行期间将加密的行附加到文件中，而不是仅仅进行一次大规模加密 - 所有内容和保存 . 虽然我有一个时间的野兽 . 这是我的加密器，经过多次尝试失败后无耻地被盗：

class Encryption
    {
        private static readonly byte[] SALT = new byte[] { 0x26, 0xdc, 0xff, 0x00, 0xad, 0xed, 0x7a, 0xee, 0xc5, 0xfe, 0x07, 0xaf, 0x4d, 0x08, 0x22, 0x3c };

        public static byte[] Encrypt(byte[] plain, string password)
        {
            MemoryStream memoryStream;
            CryptoStream cryptoStream;
            Rijndael rijndael = Rijndael.Create();
            Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(password, SALT);
            rijndael.Key = pdb.GetBytes(32);
            rijndael.IV = pdb.GetBytes(16);
            memoryStream = new MemoryStream();
            cryptoStream = new CryptoStream(memoryStream, rijndael.CreateEncryptor(), CryptoStreamMode.Write);
            cryptoStream.Write(plain, 0, plain.Length);
            cryptoStream.FlushFinalBlock();
            cryptoStream.Close();
            return memoryStream.ToArray();
        }

        public static byte[] Decrypt(byte[] cipher, string password)
        {
            MemoryStream memoryStream;
            CryptoStream cryptoStream;
            Rijndael rijndael = Rijndael.Create();
            Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(password, SALT);
            rijndael.Key = pdb.GetBytes(32);
            rijndael.IV = pdb.GetBytes(16);
            memoryStream = new MemoryStream();
            cryptoStream = new CryptoStream(memoryStream, rijndael.CreateDecryptor(), CryptoStreamMode.Write);
            cryptoStream.Write(cipher, 0, cipher.Length);
            cryptoStream.FlushFinalBlock();
            cryptoStream.Close();
            return memoryStream.ToArray();
        }
    }

这是一个虚拟函数，显示我是如何尝试它的：

private void EncryptFile(string filepath, string outputPath, string password)
        {
            FileInfo fileInfo = new FileInfo(filepath);
            string filename = fileInfo.Name;

            string fullpath = outputPath + "\\" + filename;

            BinaryWriter writer = new BinaryWriter(File.OpenWrite(fullpath), Encoding.ASCII);

            /// Two methods that I've attempted here:
            /// 1.  The desired method: encrypt line by line - I assumed I'd be able to generate
            ///     multiple blocks of data and decrypt them later.  This isn't working

            //string[] lines = File.ReadAllLines(filepath);

            /// 2.  Just read the whole thing and encrypt and write it in one swoop.

            string line = File.ReadAllText(filepath);

            //foreach(string line in lines)
            {
                byte[] bytes = Encoding.ASCII.GetBytes(line);
                byte[] encoded = Encryption.Encrypt(bytes, password);

                writer.Write(encoded);
                writer.Flush();
            }

            writer.Close();
        }



        private void DecryptFile(string filepath, string outputPath, string password)
        {
            FileInfo fileInfo = new FileInfo(filepath);
            string filename = fileInfo.Name;
            string fullpath = outputPath + "\\" + filename;

            StreamWriter writer = new StreamWriter(fullpath, false, Encoding.UTF8);

            byte[] bytes = File.ReadAllBytes(filepath);

            ///  Here is the method that's working at the moment for decrypting; just
            ///  grab all the data and decrypt it on one swoop.

            byte[] decrypted = Encryption.Decrypt(bytes, password);

            string s = Encoding.ASCII.GetString(decrypted);

            writer.Write(s);
            writer.Flush();


            ///  I've tried a number of things here to decrypt line by line,
            ///  none of which work.  This crashes with an issue about the padding
            ///  being invalid.  

            /*
            int index = 0;
            int count = 32;

            while (index

我不完全确定我应该做什么了 . 我一直在四处寻找东西并通过在线阅读示例，但它们似乎都是如何加密整个文件或只加密一段数据而不对它做任何事情，除了立即再次解密 . 我应该如何处理逐行写作？