車載網路的安全性為很重要的議題之一。在大部分的研究中，為確保車載網路的安全性，皆假設存在可靠的第三方基礎設施，並且車輛可經由路邊裝置與第三方的憑證管理中心互相通訊合作，以協助車載網路中通訊的安全。然而，現實環境中，車輛的通訊範圍內之第三方基礎設施可能不存在，或是已被攻擊，甚至已損壞不可用。因此，本論文首先提出了一個無需第三方基礎設施協助的安全架構，以群集架構為基礎，透過車輛與車輛間直接通訊，並引入PCREF [1] 的部分概念，利用多項式為基底的門檻認證機制與途中過濾機制，使車載網路於無第三方的環境仍可達到一定的安全性。此外，本論文也提出一個改進的安全架構，加入信任值、金鑰更新等概念，以加強此安全架構的安全性。最後，本論文針對機密性、資料的可信性、資料的可用性與偽造訊息的預期過濾位置來分析本架構的安全強度，並以儲存成本、計算成本與通訊成本來分析效能。依結果顯示，本論
文所提之改進安全架構能在不增加過多的成本下，提升車載網路的安全性。

The security issue is one of important issues in vehicular ad hoc networks (VANETs). To ensure the security of VANETs, most researches assumed that a third party or a basic infrastructure exists and vehicles can communicate with the certificate authority via road side units. However, the third party may not exist or has been attacked or even compromised by the attackers within the communication range of the vehicles. In this thesis, we propose a secure cluster-based framework without the third party in VANETs. The proposed framework adopts some concepts of PCREF [1] to enable the polynomial-based threshold authentication and en-route filtering scheme, reaching the security without the third party.
In addition, we propose another improved secure framework by employing the
concept of trust values for vehicles and updating of keys to enhance the security
of the framework. We then analyze the performance in terms of overhead of
storage, computation, communication as well as security strength regarding confidentiality,
data authenticity, data availability, and expected filtering position of the
bogus report. Through the performance and security strength analyses, we conclude
that the improved framework proposed in this thesis enhances the security
of VANETs greatly without an unbearable cost.

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