隨著車聯網（V2X，Vehicle-to-Everything）與智慧型運輸系統（ITS，Intelligent Transportation Systems）的發展，車輛會週期性廣播基本安全訊息（BSM，Basic Safety Message），提供位置、速度與方向等行車狀態，以提升行車安全；車輛並以假名憑證（Pseudonym Certificate）所對應的私鑰對BSM進行數位簽章，使周遭車輛得以驗證訊息來源與完整性。然而，全域被動攻擊者（GPA，Global Passive Adversary）可能長期側錄訊息，透過語法或語義鏈結，將假名變更前後的訊息重新關聯，造成位置隱私外洩。固定地點式或固定週期式假名變更策略較難因應市區交通與執法任務的即時變化，靜默時機不當亦可能影響安全通訊。本研究聚焦市區路口的執法與緊急勤務情境，提出以執法機關車輛（以下簡稱執法車輛）作為領導車輛的動態假名變更策略。系統由可信任授權中心（TA，Trusted Authority）、路側單元（RSU，Roadside Unit）與車載單元（OBU，On-Board Unit）協同運作，依執法車輛的任務路徑選定候選混合區（Mix Zone），並由RSU透過廣播和靜默期（BSP，Broadcast and Silence Period）協調普通車輛同步換名。當執法車輛接近候選混合區所在路口，且區內符合安全條件的普通車輛數達到啟動門檻時，RSU即啟動混合區，安排普通車輛短暫靜默並切換假名，使攻擊者難以鏈結新舊假名；執法車輛則持續廣播BSM，以維持安全通訊。本研究透過Veins整合OMNeT++與SUMO建立市區模擬環境。實驗結果顯示，所提策略可增加匿名集合大小、提高平均隱私熵值、降低追蹤成功率，並提升執法車輛的通行效率，而普通車輛平均速度未明顯下降。研究成果可作為未來智慧型運輸系統兼顧位置隱私、安全通訊與緊急通行需求之參考。

With the development of Vehicle-to-Everything (V2X) and Intelligent Transportation Systems (ITS), vehicles periodically broadcast Basic Safety Messages (BSMs) carrying driving status such as position, speed, and heading in order to improve driving safety. Each vehicle signs its BSMs with the private key corresponding to its pseudonym certificate, so that surrounding vehicles can verify the origin and integrity of the messages. However, a Global Passive Adversary (GPA) may eavesdrop on these messages over long periods and, through syntactic or semantic linking, re-associate the messages sent before and after a pseudonym change, thereby leaking a vehicle's location privacy. Fixed-location or fixed-interval pseudonym-change strategies adapt poorly to the real-time variations of urban traffic and law-enforcement missions; an ill-timed silence period may further undermine safety-critical communication. Focusing on law-enforcement and emergency-service scenarios at urban intersections, this study proposes a dynamic pseudonym-change strategy that uses a law enforcement vehicle (LEV) as the lead vehicle. In the proposed system, the Trusted Authority (TA), Roadside Units (RSUs), and On-Board Units (OBUs) operate cooperatively: candidate Mix Zones are selected according to the LEV’s mission route, and the RSU coordinates synchronized pseudonym changes among the regular vehicles through a Broadcast and Silence Period (BSP) schedule. When the LEV approaches the intersection where a candidate Mix Zone is located and the number of regular vehicles in the zone satisfying the safety conditions reaches the activation threshold, the RSU activates the Mix Zone and schedules a brief silence period and a pseudonym switch for those vehicles, making it difficult for the adversary to link the old and new pseudonyms; the LEV itself keeps broadcasting BSMs so that safety-critical communication is preserved. This study builds an urban simulation environment with Veins, which integrates OMNeT++ and SUMO. The experimental results show that the proposed strategy increases the anonymity-set size, raises the average privacy entropy, reduces the tracking success rate, and improves the passage efficiency of the LEV, while the average speed of regular vehicles does not decrease significantly. These findings can serve as a reference for future intelligent transportation systems that must balance location privacy, safety-critical communication, and emergency-passage needs.

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