隨時隨地可進行的網路服務仰賴於同時包含多種無線通訊技術的無線行動網路；然而，無線行動網路將資料傳輸在空氣中，比在有線網路的環境下更容易遭受安全性的威脅；除此之外，無線行動網路允許行動用戶能夠依照需求切換到其他的基地台或是服務提供者，因此有了認證者（authenticator）轉換的需求；再者，為了讓行動用戶能夠不受到切換基地台或服務提供者時所產生的影響，因而有快速切換基地台或服務提供者的需求。綜觀上述，支援認證者快轉移的網路存取控制機制在無線行動網路中有其存在之必要性。本篇論文針對網路存取控制機制，提出五個適用在無線行動網路的網路存取控制機制；以應用層存取安全、網路存取安全以及鏈結層存取安全三個面向分別說明如下：（一）應用層存取安全：第三代行動通訊系統（3G）中，IP多媒體子系統（IP multimedia subsystem；IMS）提供行動用戶多媒體服務的控制，在存取IMS應用服務前，行動用戶必須通過3G網路連結與IMS的兩道身份認證程序。這兩道身份認證程序都是以3GPP所制定的認證與金鑰協議機制（authentication and key agreement；AKA）為基礎。兩道認證程序中大部分的動作是重覆的，因而造成了效率上的問題。因此，本論文中提出了Evolutionary IMS AKA （E-IMS）與One-pass IMS AKA，不但可保有原有的安全特性，亦可比原本的方法最多增進百分之五十效率。（二）網路存取安全：本論文提出了3G與無線區域網路（Wireless LAN；WLAN）的整合機制，讓行動用戶能夠在已經擁有3G用戶帳號的情況下連結上WLAN，具有單一帳號的好處。所提出的整合機制運用了目前3GPP、IETF與IEEE 802.11i中廣泛被使用的協定，因此能簡單的建立此整合機制。而且在WLAN中，擴展認證協定（Extensible Authentication Protocol；EAP）的認證方法具有彈性，不限制單一認證方法。除此之外，與3GPP所制定的整合機制相比，本論文所提出的機制擁有較少的認證訊號花費。（三）鏈結層存取安全：為了讓行動用戶在WLAN中能夠快速地進行接取點（Access point；AP）切換，因此本論文提出了叢集鏈（cluster-chain）的結構來協助行動用戶安全資訊被事先傳送到將切換至的目的接取點，讓行動用戶與先前接取點的安全關係可快速地轉移到目的接取點。本論文同時將此機制運用到自治（autonomous）架構與中控（centralized）架構的WLAN中。

Wireless mobile networks, which contain various wireless communication technologies, can provide Internet services anytime and anywhere. However, wireless mobile networks rely on open and public transmission media. It results in that further security vulnerabilities are raised in addition to the security threats found in regular wired networks. Besides, mobile user may handoff/transit to other base stations or service providers, and meanwhile network access control mechanisms need to be raised. It results in an authenticator transition delay. Therefore, how to accelerate network access control mechanisms for facilitate authenticator transition is critical issue in wireless mobile networks. This dissertation studies network access control mechanisms, and then proposes five network access control mechanism supporting fast authenticator transition on wireless mobile networks. According to application access security, network access security, and link layer access security, the proposed mechanisms are as follows:
(I) Application access security: In UMTS IP multimedia subsystem (IMS), even when an IMS subscriber has passed the packet-switch domain authentication, the IMS subscriber's identity must be confirmed by the IMS authentication again before accessing IMS services. Both the packet-switch domain and IMS authentications are necessary for the IMS subscriber. This is the referred to as a two-pass authentication. However, the packet-switch domain authentication is carried out by the authentication and key agreement (AKA) of the 3rd Generation Partnership Projects (3GPP), called 3GPP AKA; the IMS authentication is carried out by IMS AKA. Since IMS AKA is based on 3GPP AKA, almost all of the operations are the same. It is inefficient because almost all involved steps in the two-pass authentication are duplicated. Hence, the one-pass authentication was proposed to increase the efficiency of the IMS authentication. Unfortunately, the one-pass authentication has some security problems and loses the mutual authentication and key agreement capabilities. Therefore, in this dissertation, an evolutionary IMS AKA (E-IMS AKA) and a one-pass IMS AKA in the IMS authentication are proposed to replace the IMS AKA. The proposed schemes not only adheres to the security requirements of IMS AKA, but also can be carried out in one round-trip.
(II) Network access security: Since the relationship between the 3G mobile data network and WLAN is complementary in terms of service coverage and data transmission rate, integration of 3G mobile network and WLAN can offer subscribers higher speed wireless service in hot spots and ubiquitous connectivity in 3G mobile data network. In this dissertation, we propose an authentication mechanism over the loose coupled integration mechanism using a cross-layer bootstrap. The benefits of the proposed mechanism are (a) integrating UMTS network and WLAN using the existent protocols defined in 3GPP, IETF and IEEE 802.11i, (b) the use of the EAP authentication method is flexible, (c) reduction of the authentication signaling when a subscriber roams from one access point (AP) to another AP, and (d) user identity privacy protection.
(III) Link layer access security: The latency of the basic service set (BSS) transition process in WLAN is much higher than 50ms. Since the bearable maximum delay is 50ms in multimedia applications, e.g., voice over IP (VOIP), such large handoff gap may bring up excessive jitter. Therefore, many researches make much effort about how to fast BSS transition. This dissertation proposes a cluster-chain structure, which facilitate dynamically reselect a cluster and transit to the new one to assure that STA can stay in center of the cluster. This dissertation applies the cluster-chain structure to the autonomous WLAN architecture and the centralized WLAN architecture for fast BSS transition.

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