在本研究中，我們探討運用關鍵字查詢加密檔案之議題及其發展，並針對兩種型態的關鍵字搜尋法進行深入的了解，分別是單關鍵字搜尋法及多關鍵字搜尋法，同時進一步地討論其在雲端環境中相關的安全需求。為了建構更有效率及安全的關鍵字搜尋機制，我們分別提出基於ElGamal公開金鑰系統的單關鍵字搜尋法及基於ElGamal公開金鑰系統之雙線性映射（Bilinear pairing）的多關鍵字搜尋法。此外，我們使用不須Random oracle model的正規安全性模型來分析兩種方法之安全性。 Since cloud computing has become the most popular issue in recent years, more and more cloud services have bloomed and been used worldwide such as cloud storage space, computing resource and kinds of software. When people use a cloud storage server as the daily data storage space which will replace hard discs in the desktop computer gradually, the problem of cloud security has become the most important issue in the recent studies. In order to gain the basic protection for personal documents, users usually encrypt the documents before storing them in the cloud storage server. However, as the documents are changed into the ciphertexts, no one can distinguish the content including the users who actually have the rights to download and decrypt those documents.
In this thesis, we study the issue that searching over the encrypted documents by using keyword. This research focus on two types of keyword search scheme: simple keyword search and conjunctive keyword search, and further discuss the relative requirements for security in cloud storage environment. In order to construct the more efficient and secure keyword search scheme mechanism, we proposed a simple keyword search scheme based on ElGamal public key system and a conjunctive keyword search scheme based on bilinear paring for ElGamal public key system. Furthermore, we analyze the security of each scheme in standard model without random oracle.