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Keywords
Security, Mobile communications, Multimedia, Access control, Internet
Abstract
This paper surveys the security architecture of the IP multimedia core network subsystem (IMS) of the third generation mobile system which is known in Europe as UMTS. The main features of the security architecture include user specific features protecting the access of the IMS user, such as authentication and key agreement when a user registers and integrity protection of IMS access signalling, but also features for the user, independent protection of SIP signalling in the IMS core network. Authenticated registration is given an in-depth treatment.
Introduction
3GPP (Third Generation Partnership Project), a partnership of international standardisation bodies, specifies a global third generation mobile system, known in Europe as UMTS (Universal Mobile Telecommunications System). UMTS has evolved from the second generation mobile systems GSM (Global System for Mobile Communications). Compared to GSM, UMTS offers, among many other things, enhanced security features. What is new in UMTS is the introduction of countermeasures against threats involving active attacks to masquerade or eavesdrop, and the increased focus not only on the vulnerable radio interface but also on other parts of the system, such as the signalling infrastructure in the core network. A survey of the basic 3GPP security architecture, specified in (3GPP TS 33.102, 2002) can be found in Horn and Howard (2000).
The third release of UMTS (the so-called 3GPP Release 5) contains an IP multimedia core network subsystem (IMS). Using the services of the UMTS packet domain for IP connectivity, the IMS provides the possibility to set up multimedia sessions by means of the SIP (Session Initiation Protocol) specified by the Internet Engineering Task Force (IETF) in Rosenberg and Schulzrinne (2002). The architecture of the IMS is designed such that it may use mechanisms for IP connectivity other than those provided by the UMTS packet domain in future releases. It is the aim of 3GPP to make the protocols specified for the IMS IETF-compatible.
This paper is structured as follows: following a section on the security requirements for the IMS, an outline of the security architecture is given. Then it is described in detail how an IMS user is authenticated when registering with the IMS. The following section shows how the session keys derived...