代码：

static class HandleFiles
    {
        public static void EncryptFile(string inputFile, string outputFile)   //加密
        {
            try
            {
                string password = @"12345678";
                UnicodeEncoding UE = new UnicodeEncoding();
                byte[] key = UE.GetBytes(password);

                string cryptFile = outputFile;
                FileStream fsCrypt = new FileStream(cryptFile, FileMode.Create);

                RijndaelManaged RMCrypto = new RijndaelManaged();

                CryptoStream cs = new CryptoStream(fsCrypt,
                    RMCrypto.CreateEncryptor(key, key),
                    CryptoStreamMode.Write);

                FileStream fsIn = new FileStream(inputFile, FileMode.Open);

                int data;
                while ((data = fsIn.ReadByte()) != -1)
                    cs.WriteByte((byte)data);


                fsIn.Close();
                cs.Close();
                fsCrypt.Close();


                MessageBox.Show("Encrypt Source file succeed!", "Msg :");
            }
            catch(Exception ex)
            {
                MessageBox.Show("Source file error!", "Error :");
            }
        }

        public static void DecryptFile(string inputFile, string outputFile)   //解密
        {
            try
            {
                string password = @"12345678";
                UnicodeEncoding UE = new UnicodeEncoding();
                byte[] key = UE.GetBytes(password);

                FileStream fsCrypt = new FileStream(inputFile, FileMode.Open);

                RijndaelManaged RMCrypto = new RijndaelManaged();

                CryptoStream cs = new CryptoStream(fsCrypt,
                    RMCrypto.CreateDecryptor(key, key),
                    CryptoStreamMode.Read);

                FileStream fsOut = new FileStream(outputFile, FileMode.Create);

                int data;
                while ((data = cs.ReadByte()) != -1)
                    fsOut.WriteByte((byte)data);

                fsOut.Close();
                cs.Close();
                fsCrypt.Close();

                MessageBox.Show("Decrypt Source file succeed!", "Msg :");

            }
            catch(Exception ex)
            {
                MessageBox.Show("Source file error", "Error :");
            }
        }
    }