近幾年來行動通訊設備越來越普及，其計算能力與通訊能力也不斷的提升，而行動通訊網路服務也不斷的推陳出新，從2G、3G的GSM系統甚至是目前正在極積規畫與建設的第四代行動通訊網路(4G)，行動通訊網路的服務將越來越完善。未來對行動用戶而言，盡情的使用行動通訊網路來從事工作或娛樂將不再只是夢想。然而，就如已經非常普及的有線網路一樣，在行動通訊網路上仍然存在著許多安全上的威脅，由於行動通訊網路的特性，行動用戶可以隨身攜帶著個人資料、重要的檔案或是文件，並隨時隨地的藉由行動通訊網路的服務而與外界取得聯繫。一但行動用戶進入了行動通訊網路，便開始接受來自各方的威脅，惡意的行動用戶可能藉由行動通訊網路設計上的漏洞而取得他人的重要資料。
為了保證行動通訊服務的品質，行動用戶的隱私與安全性將會是個非常重要的議題。在這篇論文裡，我們將提出一個保護行動用戶隱私與確保行動用戶通訊安全的匿名認證協定。在我們的論文裡，行動用戶不僅僅對其他行動用戶匿名，對於系統業者也具有匿名的特性，然而系統業者仍然可以對匿名的行動用戶進行計費。除此之外，我們維持著隱私權的公平性，任何行動用戶並無法藉由隱私之便而行使違法的行為，任何違規的行動用戶都會被法院或警察單位監督著，甚至撤銷其隱私權。

Mobile network equipments are widely popularized and advanced mobile communication services are provided increasingly such that ubiquitous computing environments will come true soon. It is a pleasure for mobile users to work or get recreations in the mobile network environments. However, just as the cases in wireline environments, there are a lot of security threats to mobile network systems and their impact on the security is more serious than that in wireline environments owing to the feature of wireless transmissions and the ubiquity property in mobile network systems. The secret personal information, important data, or classified missives which mobile users carry may be stolen by malicious entities. In order to guarantee the quality of the advanced communication services, the security and privacy would be the important issues when mobile users roam to the mobile networks. In this thesis, an anonymous authentication protocol will be proposed to protect both the security of the mobile network system and the privacy of mobile users. Not only does the proposed scheme provide mutual authentication between each user and the system, but also the identity of each user can be kept secret against anyone else including the system. Although the users are anonymously authenticated by the system, it can still make correct bills to charge these anonymous users. Finally, our protocol also achieves the goal of fair privacy which allows the judge to be able to revoke the anonymity and trace the illegal users when they misused the anonymity property such as they committed crimes.

1 Introduction 1
2 Related Works 5
2.1 He et al.’s Scheme: Basic User Privacy . . . . . . . . . . . . . 5
2.2 Tracz et al.’s Scheme: A Conceptual Schema for Charging
Anoymous Users . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Jakobsson and Yung’s scheme: Fair Privacy . . . . . . . . . . 9
3 Privacy Requirement in Mobile Network Environments 13
3.1 The Mobile Network Environment . . . . . . . . . . . . . . . . 13
3.2 Privacy Overview . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.3 Privacy Requirement . . . . . . . . . . . . . . . . . . . . . . . 18
3.4 Anonymity Issues . . . . . . . . . . . . . . . . . . . . . . . . . 19
4 Our Anonymous Ticket-Based Protocol 22
4.1 The Framework of Our Protocol . . . . . . . . . . . . . . . . . 23
4.2 Our Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.2.1 Buying a New Ticket . . . . . . . . . . . . . . . . . . . 25
4.2.2 Using the Ticket for Network Services at i-th Round . 28
2
4.2.3 Charging Mobile Users . . . . . . . . . . . . . . . . . . 33
4.2.4 Privacy Revoking . . . . . . . . . . . . . . . . . . . . . 35
4.2.5 Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . 36
5 Security Analysis 38
5.1 The Security Analysis on Authentication . . . . . . . . . . . . 38
5.1.1 The Replay Attack . . . . . . . . . . . . . . . . . . . . 38
5.1.2 The Impersonate Attack . . . . . . . . . . . . . . . . . 39
5.2 The Security Analysis on Blind Signatures . . . . . . . . . . . 40
5.2.1 Message Modification . . . . . . . . . . . . . . . . . . . 40
5.2.2 Message Replacement . . . . . . . . . . . . . . . . . . . 41
5.3 The Security Requirements for Each Entity . . . . . . . . . . . 42
5.3.1 The Viewpoints of Mobile Users . . . . . . . . . . . . . 42
5.3.2 The Viewpoints of the System . . . . . . . . . . . . . . 44
5.3.3 The Viewpoints of the Judge . . . . . . . . . . . . . . . 44
6 Comparisons 46
7 Discussions 49
7.1 The Double-Use Checking of Tickets . . . . . . . . . . . . . . 49
7.2 The Judge’s Device . . . . . . . . . . . . . . . . . . . . . . . . 50
8 Conclusions 52

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