如何从Firebase以Xamarin形式下载AES加密图像

Question

我正在尝试从Firebase存储下载使用AES加密的图像。我使用以下方法成功上传了图片：

private async void BtnUpload_Clicked(object sender, EventArgs e)
        {
            var fileStream = FileEncrypt(file.Path);
            var user = await GetUser(localEmail);
            await firebaseHelper.UploadFile(fileStream.Result, Path.GetFileName(file.Path), user.UserID);
            var downloadurl = await firebaseHelper.GetFile(Path.GetFileName(file.Path), user.UserID);
            await firebaseHelper.UploadURL(Path.GetFileName(file.Path), downloadurl.ToString(), user.UserID);
            await DisplayAlert("Success", "Uploaded", "OK");
        }

private async Task<FileStream> FileEncrypt(string inputFile)
        {
            var user = await GetUser(localEmail);
            FileStream fsCrypt = new FileStream(inputFile + ".aes", FileMode.Create);
            //Set Rijndael symmetric encryption algorithm
            RijndaelManaged AES = new RijndaelManaged();
            AES.KeySize = 256;
            AES.BlockSize = 128;
            AES.Padding = PaddingMode.PKCS7;
            var key = new Rfc2898DeriveBytes(user.Key, user.Salt, 50000);
            AES.Key = key.GetBytes(AES.KeySize / 8);
            AES.IV = key.GetBytes(AES.BlockSize / 8);
            AES.Mode = CipherMode.CFB;
            // write salt to the begining of the output file
            fsCrypt.Write(user.Salt, 0, user.Salt.Length);
            CryptoStream cs = new CryptoStream(fsCrypt, AES.CreateEncryptor(), CryptoStreamMode.Write);
            FileStream fsIn = new FileStream(inputFile, FileMode.Open);

            //create a buffer (1mb) so only this amount will allocate in the memory and not the whole file
            //1048576 is 1MB in binary
            byte[] buffer = new byte[1048576];
            int read;
            try
            {
                while ((read = fsIn.Read(buffer, 0, buffer.Length)) > 0)
                {
                    //Application.DoEvents(); // -> for responsive GUI, using Task will be better!
                    cs.Write(buffer, 0, read);
                }
                //fsIn.Close();//causes error
            }
            catch (Exception ex)
            {
                DisplayAlert("Error", "Error: " + ex.Message, "Ok");
            }
            finally
            {
                cs.Close();
                fsCrypt.Close();
            }
            return fsIn;
        }

但是，当我尝试下载加密文件并保存到用户Android画廊时，它无法识别文件路径，并抛出一条错误消息，指出未找到文件路径的一部分。我已检查以确保文件路径正确。 （如果我上传未加密的图像，然后使用下载URL作为我拥有的图像预览框的源，则它会成功显示图像，因此我推断出我使用的下载URL是正确的。）>

任何人都可以帮忙吗？

下面的解密和下载方法：

 private async void FileDecrypt(string inputFile, string outputFile)
        {
            var user = await GetUser(localEmail);
            FileStream fsCrypt = new FileStream(inputFile, FileMode.Open);
            fsCrypt.Read(user.Salt, 0, user.Salt.Length);

            RijndaelManaged AES = new RijndaelManaged();
            AES.KeySize = 256;
            AES.BlockSize = 128;
            var key = new Rfc2898DeriveBytes(user.Key, user.Salt, 50000);
            AES.Key = key.GetBytes(AES.KeySize / 8);
            AES.IV = key.GetBytes(AES.BlockSize / 8);
            AES.Padding = PaddingMode.PKCS7;
            AES.Mode = CipherMode.CFB;
            CryptoStream cs = new CryptoStream(fsCrypt, AES.CreateDecryptor(), CryptoStreamMode.Read);
            FileStream fsOut = new FileStream(outputFile, FileMode.Create);
            int read;
            byte[] buffer = new byte[1048576];
            try
            {
                while ((read = cs.Read(buffer, 0, buffer.Length)) > 0)
                {
                    //Application.DoEvents();
                    fsOut.Write(buffer, 0, read);
                }
            }
            catch (CryptographicException ex_CryptographicException)
            {
                DisplayAlert("Error", "CryptographicException error: " + ex_CryptographicException.Message, "Ok");
            }
            catch (Exception ex)
            {
                DisplayAlert("Error", "Error: " + ex.Message, "Ok");
            }
            try
            {
                cs.Close();
            }
            catch (Exception ex)
            {
                DisplayAlert("Error", "Error by closing CryptoStream: " + ex.Message, "Ok");
            }
            finally
            {
                fsOut.Close();
                fsCrypt.Close();
            }
        }

private async void BtnDownload_Clicked(object sender, EventArgs e)
        {
            //output path
            string galleryPath = Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryPictures).AbsolutePath;
            string outputPath = Path.Combine(galleryPath, localDownloadUrl.FileName);

            FileDecrypt(localDownloadUrl.Url, outputPath);
            await DisplayAlert("Success", "Image saved to gallery", "OK");
            await App.Current.MainPage.Navigation.PopModalAsync();
        }

我正在尝试从Firebase存储下载使用AES加密的图像。我使用以下方法成功上传了图片：私有异步无效BtnUpload_Clicked（对象发送者，...

Answer 1

所以，我终于在@Jason的很多帮助下终于解决了这个问题（请参阅评论）。