Security and Accounting Enhancements for Roaming in IMS

As the multimedia services are gaining popularity, the operators are seeking new architectures, such as IP Multimedia Subsystem (IMS), that would allow provision of these services with sufficient level of quality and security. In the future, however, it is not anymore so clear who is an operator, because the ubiquitous communication visions enables every player to interact in multitude of ways with other entities and provide services of their own. In this paper we investigate a setting, where a roaming subscriber wishes to receive service from an operator, who has no previous relationship with the home operator. We propose methods based on cryptographic identities which enable the each party to get assurance about the authenticity of each participant and the accountability of the executed actions. While suggesting completely new mechanisms for existing systems, the proposal also addresses the needs to leverage the available infrastructures in a convenient way.