The security of access procedures to mobile networks is very critical, because wireless communication can be easily compromised. So far, network access procedures to wireless networks have primarily been based on secret key techniques. In this chapter, we want to survey current secret key approaches, motivate public key approaches and present major public key protocols for network access.

8.1 Introduction

Access to wired networks raises less security concerns than access to wireless networks. The reason is that wired networks offer some inherent level of security. There is a physical link between users and networks that can only be compromised by gaining physical access to network equipment. In wireless networks, however, the security requirements are much higher because communication over the wireless air interface can be easily intercepted. Strong encryption to prevent eavesdropping and tampering, and mutual authentication of user and network to ensure that sensitive information is transmitted only to the legitimate network are, therefore, necessary [1].

Network access security constitutes a group of security features providing mobile users with secure access to a serving network. The wireless part of the connection, the so-called radio access link, requires particular protection. For example, in Universal Mobile Telecommunications System (UMTS) the network access security comprises the following features.

• Mutual authentication of user and serving network.

• Confidentiality - user traffic and signalling data needs to be encrypted over the radio link.

• Anonymity - confidentiality of the mobile user's identity over the radio link. In UMTS, this is achieved...