本研究針對無線感測網路時間同步協定中，發展最為成熟的氾濫式時間同步協定(Flooding Time Synchronization Protocol, 簡稱FTSP)來進行改良。FTSP的設計著重於支援動態網路配置與全域時間的精確度，但是原始的設計並沒有考量安全性的防護，使得它在時間同步進行過程中容易遭受惡意節點的攻擊。因此，加強時間同步協定的安全是非常急迫的研究議題。
Tanya等人的先行研究把針對FTSP的攻擊分為根節點攻擊與一般節點攻擊兩類，再將一般節點攻擊細分為針對globalTime、seqNum與發送頻率等三種攻擊方式。因此，在分析完FTSP的架構後，我們對於根節點的攻擊提出了根節點選擇機制來公平並安全的選擇出根節點；而在節點資訊收集的方式上，則提出參考節點選擇機制來避免多重參考節點對時鐘偏斜精確度的影響，並在FTSP中加入時間同步過濾器來濾除不正常的時間同步訊息。在時間同步過濾器中包含有:針對globalTime欄位攻擊的鄰近節點全域時間黑名單過濾器、針對seqNum欄位攻擊的鄰近節點全域時間黑名單過濾器、用來判別參考節點身分的時鐘偏斜過濾器，與將誤差矯正造成的影響降低的震盪過濾器。以上所提出的防禦機制應足以對時間同步的運行提供合理的安全性。
由於根節點選擇機制中，封包傳遞的防護是運用現有的金鑰加密，因此在模擬攻擊的實驗上，只針對除了根節點選擇外所設計的防禦機制進行測試。在模擬實驗中，鄰近節點全域時間黑名單過濾器與鄰近節點seqNum黑名單過濾器成功達到過濾惡意節點針對globalTime與seqNum的攻擊。藉由參考節點的時鐘偏斜震盪範圍在1ppm內的特性，可以透過時鐘偏斜過濾器來辨識參考節點的身分。並且利用震盪過濾器，讓原本收集到錯誤資訊時需等待10個週期時間才能重新獲得正確的時鐘偏斜，降低至5個週期時間就可以完成修正，並且可以避免發送錯誤的時間同步訊息。因此，從實驗得到的結果顯示，本研究中所提出的防禦機制，可以有效彌補過去研究所提到安全性的漏洞。

This research tries to complement the security vulnerability of Flooding Time Synchronization Protocol (FTSP), which is currently known as the most sophisticated time synchronization protocol in wireless sensor networks. FTSP has advanced features like implicitly dynamic topology and high accuracy time, but its original design does not consider security issues. This makes malicious nodes be able to easily break the time synchronization protocol and change the time of synchronization messages. In order to defend attacks from malicious nodes, the mechanism of FTSP has to be reinforced by adding security components. According to the literature, assaults on FTSP are divided into two categories: the attack on the root node and the attack on normal nodes. The later type can be further subdivided into three different cases: (1) modifying the globalTime field; (2) modifying the seqNum field; (3) reducing the frequency of sending packets. After analyzed the structure of FTSP, we propose a root node election mechanism which benefit from base station to defend the first type attacks. In order to defend attacks on normal nodes, reference node selecting mechanism and several data filters are proposed. The proposed data filters include black lists of neighbor globalTime filter, black lists of neighbor seqNum filter, clock skew filter and time fluctuation filter. By applying these enhanced components, the security of FTSP can be assured.
Since the root election mechanism utilizes data encryption which is shown to be effective by previous studies, only experiments of normal node attacks are performed. The results of experiments show that we have successfully defended the seqNum attack and the globalTime attack by using black lists of neighbor seqNum filter and black lists of neighbor globalTime filter. By applying the characteristics of fixed clock skew fluctuation, around 1ppm, reference node can be successfully identified. Furthermore, the data collection time automatically drop from 10 sending cycles to 5 sending cycles under a globalTime attack by utilizing time fluctuation filter. From our experimental result, the proposed filters can improve the security of FTSP and fix the vulnerabilities caused by original design.

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