隨著雲端服務的快速發展以及個人隱私保護的需求提升，雲端加密儲存服務和安全的密文搜尋儼然成為重要且實用的議題。本論文探討的主題是加密影像的安全搜尋，相同於受到廣泛討論的加密文件搜尋，影像同樣具有豐富的隱私資訊，例如：外表、身分證、駕照…等，要如何防止資料擁有者、雲端伺服器、使用者惡意搜集服務過程中的零碎資訊並攻擊系統服務的任何單元正是本論文的主要目標。近年來，隱私保護運算一直受到高度的關注，其中又以非對稱式內積保護加密 (Asymmetric scalar-product-preserving encryption：ASPE) 和同態加密 (Homomorphic encryption：HE) 最為常見，但金鑰洩漏疑慮以及運算和通訊成本過高造成兩者在隱私安全運算上無法應用於現實情況。本研究中，我們在非對稱式內積保護加密的安全運算系統下，藉由引入同態加密的技術可以避免金鑰和使用者查詢資料的洩漏，並且使用輕量化的存取控制來驗證使用者的身份和查詢是否經過偽造。結合上述兩者方法，可以防止檔案擁有者非法搜集使用者的查詢資料和雲端伺服器猜測搜尋樹的結構以及來自內部使用者的金鑰洩漏，讓該系統更適合於現實環境。

Owing to the rapid development of cloud services and personal privacy demand, secure search over encrypted cloud storage services become an important issue. Images might leak sensitive information just like text files. For example, the leakage of identification or driver’s license will lead to serious situation. The trend towards secure computation has been widely discussed, especially asymmetric scalar-product-preserving encryption (ASPE) and homomorphic encryption (HE). Although ASPE has ability to encrypt and determine the similarity between ciphertexts efficiently, it is not a practical methodology assuming that users are fully trusted in real world. Contrary to ASPE, HE can perform addition and multiplication in the encrypted domain and solve the problem of key leakage. However, it brings great communication and computation costs. In this thesis, we propose a privacy-preserving content-based image retrieval with key confidentiality scheme (SIRKC) against attacks for the data owner, cloud server and users. Through combining HE and ASPE, our scheme ensures the confidentiality of key and privacy of query details. In addition, we provide a verification method to check whether the query is fake or not. The experiment results show that the computational overheads and reduction in search precision are acceptable. Our proposed scheme is effective to provide an image retrieval search in encrypted cloud data storage.

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