在VANET的環境中車輛所提供的交通訊息安全性是很重要的，車輛訊息需要即時性並且驗證訊息計算複雜度不能太高，本文提出方法主要是以雙線性方法進行身分驗證，讓車輛、RSU、CA以及TA之間可以互相驗證身分真實性，並且車輛透過與RSU驗證身分後，將車輛的變色龍函數值傳送給其他RSU以及車輛，其它車輛可以透過發訊者的函數值與從RSU得來的變色龍函數來進行驗證。
本文提出方法的優點主要為：1.車輛、RSU、CA以及TA可以透過IBC相互驗證訊息，2.車輛可以自行驗證public/private key的合法性以及發行的來源3.車輛不需要出示任何證書就可以驗證身分，避免證書長期暴露遭到攻擊，4.透過變色龍函數可以驗證車輛訊息，不需等待RSU驗證訊息，可以提高訊息的即時性，5.車輛在不同RSU範圍Hand-off時，不需要重新驗證身分以及協商common key，6.本文提出方法除了在RSU範圍的車輛，並且也可以運用在沒有在RSU範圍的車輛上，理由可參考第4點。本文提出方法可以滿足訊息來源性、完整性、不可否認性、隱私以及不可追蹤性。

In the VANET environment, the security of traffic information between vehicles is very important. The messages need to be real-time, and the complexity of authentication should be low. Our proposed method focus on the identity verification based on bilinear pairing, therefore, vehicles, roadside units (RSUs), central authorities (CAs) and trust authority (TA) can verify the identity of each other. After the identity authentication, RSUs will broadcast messages containing chameleon hashing values of verified vehicles, to the other RSUs and vehicles. In the future, vehicles can communicate with the verified vehicles, and verify the messages by these chameleon hashing values.
The advantages of the propose method is mainly: 1. Based on the identity-based cryptography (i.e. IBC), the vehicles, RSUs, CAs and TA can verify the message each other. 2. The vehicles can verify the source and legitimacy of the public/private key. 3. The vehicles do not need to show any certificate to verify the identity, avoiding the certificate is exposed for a long time and causing attacks. 4. We can verify the messages through chameleon function and does not need to wait for RSU to verify, it would have good latency performance. 5. We don’t need to re-verify the identity and consult the common keys when the vehicles hand off within the different cover ranges of the RSUs. 6. Not only within the RSUs, our proposal but also can execute in somewhere without RSU. Finally, our proposal method can fulfill the authentication, data integrity, non-repudiation, condition-privacy and untraceable.

Chapter 1 Introduction 1
1-1 Vehicular Ad-Hoc Network 1
1-2 Motivation 4
1-3 Thesis Organization 5
Chapter 2 Related Works 6
Chapter 3 System Model 9
3-1 System Environment 10
3-2 Identity-based Cryptography (IBC) 11
3-3 The Chameleon Hashing 13
3-4 System Initialization 15
3-5 Registration 17
3-6 Setting the Transmission Packets Format 19
Chapter 4 Proposed Scheme 21
4-1 Identity Verification 22
4-2 Message Broadcast and Message Authentication in RSU 24
4-3 Vehicles’ PID and Key Updating 26
4-4 Vehicles’ Key Updating without coverage RSU scenario 27
4-5 Vehicles’ Message Authentication without coverage RSU scenario 28
Chapter 5 Security and Performance Analysis 29
5-1 Security Analysis 30
5-2 Performance Analysis 31
Chapter 6 Conclusion and Future Work 35
References 37

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