為了減少交通事故、提供緊急交通資訊及增加開車的舒適度，車輛隨意網路(Vehicular ad hoc networks) 在近幾年吸引了許多學者的注意。車輛隨意網路與傳統無線網路最大的不同在於使用者的注意力不可被影響，否則可能會造成生命財產的損失。此篇論文中，我們展現了一種新的網路安全威脅，此安全威脅的原理為，利用偽造的交通安全訊息來誤導駕駛人，進而控制駕駛行為。惡意攻擊者可利用此安全弱點來造成交通事故，或減低車輛隨意網路的網路效能。我們提出了以交通事件為基礎的名譽系統，來防治此種攻擊。在此系統下，車輛彼此合作蒐集交通事件的證據，只有在證據足夠時，系統才會認為此交通事件是真正存在的。我們使用網路模擬來分析與評估所提出的名譽系統，結果顯示我們所提出的系統可在絕大部分的車輛隨意網路環境下運作，且可以有效解決各種偽造訊息所造成的影響。

Vehicular ad hoc networks (VANET) have drawn a lot of attention in resent years in terms of novel applications to reduce car accidents, provide emergency information, and create more comfortable driving experience on roadways. The main difference between vehicular ad hoc networks and other traditional wireless networks is the driver’s attention can not be distracted because driving safety in a matter of life and death. In this thesis, we show a new security threat that fraud messages could disturb the drivers’ attention. The attacker can use this weakness to control the drivers’ behavior that could cause traffic accidents, traffic jam or decreasing the VANET performance in terms of bandwidth utilization. To defend against this kind of attack, we proposed a event-based reputation system. In this system, vehicles collect the evidence of the traffic event cooperatively. The traffic event is trustworthy only if the reputation system collects enough reputation value and signatures about this event. The proposed solution is characterized and evaluated through extensive simulation. The result of simulation shows that our system is suitable in most VANET environments and can defend against all kinds of bogus messages.

Contents
中文摘要I
AbstractII
誌 謝III
ContentsIV
List of FiguresVI
List of TablesVII
Chapter 1.Introduction1
Chapter 2.Security of traffic safety application5
Chapter 3.Environment models and problem statement10
3.1Network model10
3.2Security model11
3.3Problem statement11
Chapter 4.Event-based reputation system on VANET13
4.1Traffic event generation15
4.2Collaboration observation mechanism17
4.3Message verification19
4.4Reputation value suppression20
4.5Adaptive reputation threshold and event signature threshold21
4.5.1Reputation threshold22
4.5.2Event signature threshold24
Chapter 5.Traffic event management on VANET27
5.1Event intensity27
5.2Event movement and erasion29
5.3Event information update30
Chapter 6.Simulation31
6.1Performance analysis32
6.2Security analysis42
Chapter 7.Discussion46
7.1Comparisons to similar work46
7.2Limitations48
Chapter 8.Related work50
Chapter 9.Conclusions54
Reference55

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