近年來，車輛網路慢慢的受到了重視。這是由於車輛網路有一些良好的應用，像是在車輛安全方面以及在一些服務應用上（電子地圖下載、上網服務等等）。前者應用所發出的訊息我們稱之為路況訊息，後者應用所發出的訊息則稱之為常務訊息。而這些訊息中，以路況訊息最為重要。在車輛行駛中，若發生了車輛意外或是路況擁塞等情況，這時透過了車輛網路的傳遞，把這些事件訊息即時廣播給其他車輛，使其提早獲得警訊，就可以避免其他的車輛捲入這場意外或讓路況不再更為擁塞。這樣的訊息是攸關生命安全的，因此，當傳播這些訊息的時候，要注意到的是這些訊息的正確性。也就是說，這些訊息是否會被不法份子給偽造、修改的情形，而造成交通的大亂，這是我們所不允許的。所以車輛網路的網路安全就受到了重視，這也是本論文的重點。
在對於車輛網路的訊息認證已經有許多的研究提出了一些方法，但這些方法有的使車輛計算負擔太重，有的有其不完整的缺點。而本論文則是整合了這些研究的方法，提出了改善了這些缺點的方法。第一個方法是在有路側單元的情況下，路用路側單元的協助來進行訊息認證。第二個則是針對無路側單元的情況下，利用群組的組成，以群為單位，每台車輛進行排程的輪流認證機制。這兩個方法都能在有效減少計算負擔的前提下，形成一個完善的訊息認證系統。

In the recent years, it comes into more notice for Vehicular Ad-hoc Network (VANET) due to good applications of VANET. For example, those applications include the driving secure and some serviced applications (e.g., loading electric maps, web Service, and so on). The delivered message about driving secure is called the traffic messages, and the delivered message about serviced applications is called the routine message. The traffic message is more important than the routine message. When vehicle is driven on the road and the events are happened (example of accident, or jam), it can broadcast these happened events to notify others on the same road by VANET and let others to earlier get the awareness to avoid the more serious accident or traffic jam. In fact, these traffic messages are related to the life of driver and passengers. Thus, we must pay attention to the correctness of these traffic messages when these messages are sent in VANET, i.e., it will result the serious traffic disorder if these messages are altered or forged by illegal offenders and we don’t permit this situation to occur. Hence, the network security in VANET is the emphasis in this paper.
There are some studies that have proposed some scheme for message authentication in VANET. However, there still exist some imperfections in these schemes (for example, the communication overhead is too heavy). Thus, this thesis proposes two schemes to improve these drawbacks based on some schemes which had been proposed. The first proposed scheme verifies message with the RSU’s aid in the RSU scenario. The second proposed scheme uses the clustering to work a rotation for verifying message for no RSU scenario. The two schemes can efficiently reduce the communication overhead to form an integrity message authentication system.

中文摘要………………………………………………………………………………i
Abstract………………………………………………………………………………..ii
List of Figures………………………………………………………………………...iii

Chapter 1 Introduction…………………………………………………………….1
1-1 Vehicular Ad-Hoc Network…………………………………………………..1
1-2 Motivation……………………………………………………………………3
1-3 Thesis Organization…………………………………………………………..5

Chapter 2 Related Works……………………………………………………….....6
2-1 RAISE Scheme……………………………………………………………….6
2-2 COMET……………………………………………………………………...10
2-3 TESLA One-way hash chain…………………………………………………13
2-4 DDVC………………………………………………………………………..15

Chapter 3 Proposed Schemes………………………………………………….....17
3-1 Proposed Scheme-1…………………………………………………………..17
3-1-1 Common Secret Key Establishment……………………………….....17
3-1-1-1 Case 1: Enter for the first time………………………………...17
3-1-1-2 Case 2: Enter for the second or more times…………………...20
3-1-2 Aggregated Hash……………………………………………………...21
3-1-3 Message Verification for Receivers…………………………………...22
3-1-4 Communication between Different RSUs……………………………24
3-1-4-1 Problem Statement…………………………………………….24
3-1-4-2 Solution………………………………………………………..25
3-1-5 Handoff Problem……………………………………………………...26
3-1-5-1 Problem Statement…………………………………………….26
3-1-5-2 Solution………………………………………………………...27

3-2 Proposed Scheme-2……………………………………………………….......29
3-2-1 First-Stage Clustering Scheme………………………………………...29
3-2-1-1 The DV Cost for Clustering……………………………………29
3-2-1-2 The DDVC algorithm………………………………………….30
3-2-2 Second-Stage Clustering Scheme……………………………………..32
3-2-3 Schedule Management & Cluster Maintenance……………………….35
3-2-3-1 Join……………………………………………………………..36
3-2-3-2 Leave…………………………………………………………...37
3-2-3-3 Overlap of clusters…………………………………………….38
3-2-3-4 Clusterhead is destroyed………………………………………38
3-2-4 Verification……………………………………………………………39

Chapter 4 Conclusion……………………………………………………………...41
Reference…………………………………………………………………………….42

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