先進交通管理系統乃是智慧運輸系統的核心系統，目前NTCIP (National Transportation Communications for ITS Protocol)已被許多國家採用作為其先進交通管理系統標準傳輸協定之參考，其係依循國際標準組織開放式之架構，因此可相容於現行一般網路通訊協定，但開放式網路環境也為NTCIP帶來安全性問題。而實際應用上，先進交通管理系統資料傳輸之安全性往往為人們所忽略。故本研究透過密碼學技術，針對資料傳輸之確認性、機密性與完整性，對傳輸訊息進行加密保護，以提高其傳輸安全性；此外亦提供一套無須增加金鑰長度，亦可確保封包安全之動態加密技術。在實驗設計中，利用統計分析確認封包加密所造成之影響幅度；並分析加密前後之封包於區域網之傳輸耗時的可靠度，使採用加密機制之交控中心人員能依可靠度需求，訂立相關傳輸耗時之門檻值，以建構適用於交控系統之資訊安全機制，使其達成資訊安全之同時亦避免浪費通訊資源。

Advanced Transportation Management Systems (ATMS) is the major sub-system of ITS. The NTCIP (National Transportation Communications for ITS Protocol) which incorporates ISO-OSI structure and can be compatible with Internet protocols has been followed by many countries. Although security issue arose from its open environment, more often than not, this was ignored by traffic engineers practically. Therefore, this paper aims at designing a suitable and securer system combining symmetric cryptography with asymmetric cryptography as a hybrid cryptosystem to ensure the transmission security of ATMS data, especially in terms of their authentication, confidentiality and integrity. In addition, a dynamic encryption technique is utilized to improve security level without increasing the length of encryption key. In order to recognize the effects resulting from encryption and decryption of transmission data, three experiments are designed and executed within this system. Statistical analysis is also applied to test and verify the influence induced by this extra secure mechanism comparing to the no encryption situation. Finally, reliability analysis based on experimental data is brought out in this study. Thereupon ATMS operators can select proper threshold for transmission time according to the requirement of reliability. The hybrid cryptosystem applied in this research provides ATMS with both securer and more efficient way for data transmission, and avoids waste of communication resources.