近年來，人們對於雲端儲存空間服務的需求逐漸增加。然而，在眾多的雲端儲存空間服務中，不同的供應商都有其不同的限制，造成了使用者的不便。而最令人詬病的缺點，就是使用者已經刪除檔案，也無法確信雲端儲存空間中的檔案也一樣被完全抹除，檔案的隱私性遭受懷疑。先前已有其他工作提出了一個系統架構，讓使用者透過單一窗口管理多個雲端儲存空間，彷彿每個雲端儲存空間都串連在一起，使用者可以隨著自己的需求增加或刪除空間，也能對雲端上的檔案進行加密，增加檔案的隱私性。

但是在該架構下，維持此服務的伺服器會有過多的負擔，而其他由第三方加密的類似服務，也無法有效地實現差異同步。為了解決上述的問題，我們提出了一個新方法。

在Rsync演算法的幫助下，我們提出了Fragment Rsync演算法。我們會把檔案以一定範圍的大小切成數個Fragment並做加密，將檔案以Fragment的形式存放在雲端儲存空間中，在往後對檔案進行修改時，會以Fragment為單位來對雲端儲存空間上的檔案進行差異同步。在這個方法下，與其他的第三方服務相比，即使檔案經過第三方加密，也能達到盡量只同步新舊檔案差異的部分，省下傳輸的流量與時間，而客戶端也不再需要將檔案的任何部分傳至伺服器，從而大幅減少伺服器的負擔，也提升了檔案的隱私性。

In recent years, there is a growing demand for cloud storage services. However, in many cloud storage services, different providers have their different restrictions, resulting in the user's inconvenience. The most criticized defect is that users can’t be sure whether the file they deleted is really gone forever in the cloud storage. The privacy of files is in question. Other work has proposed a system which allows users to manage multiple cloud storage spaces in a single window, as if all of them are concatenated. Users can add or delete space as needed, and also can encrypt their data, increasing the privacy.

However, the system will cause too much burden on the server maintaining the service to do so. And the encryption service provided by third parties can’t effectively achieve differential synchronization. In order to solve the problem, we come up with a new method.

Under the assistance of Rsync algorithm, we present the “Fragment Rsync” algorithm. We divide the file into certain size of “fragments", encrypt them, and save the file in the cloud storage as the form of “fragments”. When files are modified in the future, the differences we make will be synchronized to the data in the cloud storage in the unit of “fragment”. By applying this method, even if the data is encrypted by a third party, this can save the time and network traffic by only synchronize the differences between the original and revised file to the best. Users will not need to transfer any part of the file to the server anymore, which loosen the burden of the server and at the same time, elevate the privacy of the file.

[1] “Dropbox official website”, Dropbox, [Online]. Available:
https://www.dropbox.com/.
[2] “Google Drive official website”, Google Drive, [Online]. Available:
https://drive.google.com/.
[3] “Box official website”, Box, [Online]. Available:
https://www.box.com/.
[4] “OneDrive official website”, OneDrive, [Online]. Available:
https://onedrive.live.com/.
[5] Daemen, J. & Rijmen, V. (2013). The design of Rijndael: AES-the advanced
encryption standard. Springer Science & Business Media.
[6] Chu, Y.C. (2015). A System for Integrating Multiple Cloud Storage Services:
Implementation of Secured and Synchronized Desktop. Unpublished doctoral
dissertation, National Tsing Hua University, Taiwan
[7] Tridgell, A., & Mackerras, P. (1996). The rsync algorithm(Tech. Rep. No.
TR-CS-96-05).
[8] “SQLite official website”, SQLite, [Online]. Available:
https://www.sqlite.org/.
[9] “Microsoft SQL Server 2012”, Microsoft, [Online]. Available:
http://www.microsoft.com/zh-tw/download/details.aspx?id=29062.
[10] Chen, W.K. (2015). A System for Integrating Multiple Cloud Storage Services:
Solution for Building Service-Oriented Servers. Unpublished doctoral
dissertation, National Tsing Hua University, Taiwan
[11] Walls, C. (2005). Embedded Software: The Works(344). Elsevier.
[12] “JNotify official website”, JNotify, [Online]. Available:
http://jnotify.sourceforge.net/.
[13] “Java official website”, Java, [Online]. Available:
https://java.com/zh_TW/.
[14] “Boxcryptor official website”, Boxcryptor, [Online]. Available:
https://www.boxcryptor.com/.