隨著網際網路迅速的發展及雲端運算的崛起,其中社群網路服務最受歡迎。在社 群網站中因需要大量存儲個人信息,因此隱私問題也越來越被受重視。除此之外,社 群網站都是透過廣告行銷的收益維持營運。然而,若使用者將其傳送之內容加密,則 社群網站供應商便無法從中找出精準的廣告,如此一來廣告的效益將會大幅降低。因 此,如何以保障使用者隱私為前提,並兼顧有效投放廣告是社群網站研究中的重要待 解議題。
有鑑於此,我們首先提出了應用於社群網站中可以多方傳送的謂詞搜尋加密機制。 我們提出的加密機制可以抵抗惡意的使用者及社群網站供應商,也同時滿足保護使用 者隱私和有效率的投放廣告的特性。相較於將傳統謂詞加密機制套用於社群網站中, 我們所提出之機制有更低的通訊成本。

Among the applications of the internet and cloud computing, OSNs is the most popular one. Since lots of personal information will be stored on the OSN platform, the privacy issue on such application has become more and more important. Apart from this, OSN platforms need advertisement revenue to enable continued operations. However, if the users encrypt their messages, then OSN providers cannot generate accurate advertisement to users. Thus how to achieve both privacy preserving and accurate advertisement is a worth-discussing issue. Un- fortunately, none of the researches on OSNs can achieve both privacy preserving and accurate advertisement simultaneously.
In view of this, we propose the first multi-receiver predicate encryption scheme for OSN platforms. Our scheme can not only protect the users’ privacy but also achieve customized advertisement. Compared with other predicate encryption scheme used in OSN platforms, our scheme achieve shorter ciphertext length. The semantic security and attribute hiding are also proved in the standard model.

論文審定書i
Acknowledgments iv
摘要v
Abstract vi
List of Figures x
List of Tables xi
Chapter 1 Introduction 1
1.1 Contributions...................................... 2
1.2 Organization ...................................... 3
Chapter 2 Preliminaries 4
2.1 OnlineSocialNetworksModel............................ 4
2.2 AsymmetricPredicateEncryption .......................... 5
2.3 BilinearGroupsofCompositeOrder......................... 6
2.4 ComplexityAssumptionsandHardProblems ................... 6
2.4.1 SubgroupDecision(SD)Assumption[9] ................. 6
2.4.2 Bilinear Subgroup Decision (BSD) Assumption [9] . . . . . . . . . . . 7
Chapter 3 Related Works 8
3.1 Katz et al.’sScheme[9] ............................... 8
3.1.1 Review of Katz et al.’sScheme1...................... 8
3.1.2 Review of Katz et al.’sScheme2...................... 10
3.1.3 Review of Katz et al.’sScheme3...................... 11
3.2 Lewko et al.’sScheme[13] ............................. 11
3.2.1 Review of Lewko et al.’sScheme...................... 11
3.3 Okamoto et al.’sScheme[20] ............................ 12
3.3.1 Review of Okamoto et al.’sScheme1 ................... 12
3.3.2 Review of Okamoto et al.’sScheme2 ................... 13
3.4 Kawai et al.’sScheme[11] .............................. 14
3.4.1 Review of Kawai et al.’sScheme1..................... 14
3.4.2 Review of Kawai et al.’sScheme2..................... 16
3.5 Lin et al.’sScheme[17]................................ 17
3.5.1 Review of Lin et al.’sScheme........................ 18
3.5.2 Comments on Lin et al.’sProtocol ..................... 20
Chapter 4 The Proposed Scheme 22
4.1 Overview ........................................ 22
4.2 Multi-Receiver Predicate Encryption ........................ 22
4.2.1 Definition of Multi-Receiver Predicate Encryption . . . . . . . . . . . . 23
4.2.2 The Proposed Scheme ............................ 23
4.3 Construction of the OSN Platform.......................... 27
4.3.1 An Example of Multi-Receiver Predicate Encryption . . . . . . . . . . 29
Chapter 5 Security Proofs 34
5.1 MaliciousKGC(OSNs)................................ 34
5.1.1 Security Analysis............................... 34
5.2 Security Against Malicious Users .......................... 35
5.2.1 Security Model of Semantic Security.................... 35
5.2.2 Security Proofs of Semantic Security.................... 36
5.2.3 Security Model of Attribute Hiding..................... 39
5.2.4 Security Proofs of Attribute Hiding..................... 40
5.2.4.1 Indistinguishability Between Game0 and Game1 . . . . . . . 41
5.2.4.2 Indistinguishability Between Game1 and Game2 . . . . . . . 43
5.2.4.3 Completing the Proof of Hybrid Games . . . . . . . . . . . . 46
Chapter 6 Comparisons 48
6.1 PropertiesComparisons ................................ 48
6.2 SecurityComparisons ................................. 50
Chapter 7 Conclusions and Future Works 52
Bibliography 53

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