/// <summary>
/// Decrypt a Message and download the blobs of the Message (e.g. image or file)
/// </summary>
/// <param name="threemaId">Threema ID of the sender</param>
/// <param name="messageId">Message ID</param>
/// <param name="box">Encrypted box data of the file/image message</param>
/// <param name="nonce">Nonce that was used for message encryption</param>
/// <param name="outputFolder">Output folder for storing decrypted images/files</param>
/// <returns>Result of message reception</returns>
public ReceiveMessageResult ReceiveMessage(string threemaId, string messageId, byte[] box, byte[] nonce, string outputFolder)
{
//fetch public key
byte[] publicKey = this.apiConnector.LookupKey(threemaId);
if (publicKey == null)
{
throw new InvalidKeyException("invalid threema id");
}
ThreemaMessage message = CryptTool.DecryptMessage(box, this.privateKey, publicKey, nonce);
if (message == null)
{
return(null);
}
ReceiveMessageResult result = new ReceiveMessageResult(messageId, message);
if (message.GetType() == typeof(ImageMessage))
{
//download image
ImageMessage imageMessage = (ImageMessage)message;
byte[] fileData = this.apiConnector.DownloadFile(imageMessage.BlobId);
if (fileData == null)
{
throw new MessageParseException();
}
byte[] decryptedFileContent = CryptTool.Decrypt(fileData, privateKey, publicKey, imageMessage.Nonce);
FileInfo imageFile = new FileInfo(outputFolder + "/" + messageId + ".jpg");
using (FileStream stream = File.OpenWrite(imageFile.FullName))
{
stream.Write(decryptedFileContent, 0, decryptedFileContent.Length);
stream.Close();
}
result.Files.Add(imageFile);
}
else if (message.GetType() == typeof(FileMessage))
{
//download file
FileMessage fileMessage = (FileMessage)message;
byte[] fileData = this.apiConnector.DownloadFile(fileMessage.BlobId);
byte[] decryptedFileData = CryptTool.DecryptFileData(fileData, fileMessage.EncryptionKey);
FileInfo file = new FileInfo(outputFolder + "/" + messageId + "-" + fileMessage.FileName);
using (FileStream stream = File.OpenWrite(file.FullName))
{
stream.Write(decryptedFileData, 0, decryptedFileData.Length);
stream.Close();
}
result.Files.Add(file);
if (fileMessage.ThumbnailBlobId != null)
{
byte[] thumbnailData = this.apiConnector.DownloadFile(fileMessage.ThumbnailBlobId);
byte[] decryptedThumbnailData = CryptTool.DecryptFileThumbnailData(thumbnailData, fileMessage.EncryptionKey);
FileInfo thumbnailFile = new FileInfo(outputFolder + "/" + messageId + "-thumbnail.jpg");
using (FileStream stream = File.OpenWrite(thumbnailFile.FullName))
{
stream.Write(decryptedThumbnailData, 0, decryptedThumbnailData.Length);
stream.Close();
}
result.Files.Add(thumbnailFile);
}
}
return(result);
}