伴隨著雲端技術的發展，雲端儲存技術日趨成熟，例如Dropbox、Google Drive等，在Windows、iOS、Android上均有其用戶端應用程式，消費者越來越樂於將數據儲存於雲端儲存服務中，享有高品質隨時隨地讀寫與分享的需求的解決方案。除此之外，對企業而言，將數據儲存的工作交由雲端儲存服務提供商處理比起往常建立數據中心處理更加可以降低數據管理與硬體維護的成本。因此，享用雲端儲存服務的使用者越來越多，所儲存的數據量也非常快速地成長。漸漸地，文件搜尋的功能顯得不可或缺。
然而，雲端安全成為議題，使用者瞭解到即便有完整且安全的數據管理機制，也不足以完全避免攻擊者存取商業資訊或私人資訊的可能性。越來越多單人使用的密文搜尋架構被提出，讓使用者可以在密文的環境下做多種關鍵字搜尋，但如此卻犧牲了雲端可方便與他人共享檔案的好處。
因此我們提出可用於多人分享的密文搜尋平台，讓使用者除了可以搜尋自己的檔案外，也可將檔案分享給其他授權使用者做關鍵字搜尋，且在關鍵字及檔案部份仍使用對稱式加密法，保留單人使用密文搜尋的效率及安全性，同時加上可與他人分享的功能增添系統的實用性及方便性。

With the technical development of cloud computing, more and more company
provide their own cloud storage, such as Dropbox, Google Drive, Sky Drive etc..
Some of them also provide mobile application on Windows, iOS, and Android sys-
tem. To individual users, they could access their data anytime and anywhere by
storing their data on cloud storage. They could also save space of their own PC
storage. To enterprises, compared with building a conventional data center, they
could reduce the cost of data management and maintenance of hardware devices by
using the service supplied by cloud provider. Due to plenty of advantages above,
more and more people enjoy using cloud storage. And the amount of data stored in
the cloud increases rapidly. As a result, the searching functionality is indispensable.
However, the cloud security became a significant issue, users figured out that
even if the storage providers apply secure data management mechanism, it is still
possible for hijacker to steal users' credentials and secret of the commerce. Thus,
more and more single user keyword search on encrypted data were proposed. Users
could perform different keyword search without decrypting data. However, encrypt-
ing files before uploading scarified the advantage of the convenience of sharing data
with others on the cloud.
Consequently, we aimed to design a searchable encryption for multi-user. Data
owners could share their data with authorized users without directly sharing their
data keys. We combine the advantage of effciency of symmetric encryption with
authentication of asymmetric encryption to provide a secure and effcient system of
shareable keyword search on encrypted data.

Contents
Table of Contents i
List of Figures iii
List of Tables iv
1 Introduction 1
2 Related Work 4
3 Design 7
3.1 Design Goal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Basic Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 Design of Proposed Scheme . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.1 Key Generation . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.2 Key Management . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.3 Create Secure Index/Data . . . . . . . . . . . . . . . . . . . . 13
3.3.4 Authentication Mechanism . . . . . . . . . . . . . . . . . . . . 13
3.4 Denition of Shareable Keyword Search . . . . . . . . . . . . . . . . . 13
3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4 Key Generation 18
4.1 Generating password for authentication . . . . . . . . . . . . . . . . . 18
4.2 Generating short-term KD and short-term KW for dierent shared les 19
4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5 Implementation 21
5.1 Programming Language and Server database . . . . . . . . . . . . . . 21
i
5.2 System Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.2.1 Signup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.2.2 Login Process . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.2.3 Upload the le . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.2.4 Retrieval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.3 Search Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.4 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6 Conclusion and Future Work 37

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