Abstract
In the third generation mobile telecommunication systems such as UMTS, one of the important problems for value-added services is to check the recoverability of costs used by a mobile user. In this paper we present an efficient public-key protocol for mutual authentication and key exchange designed for value-added services in UMTS. Proposed ticket based authentication and payment protocol provides an efficient way for VASP to check the recoverability of costs without communication with the on-line TTP. Furthermore, ticket based protocol can provide anonymous service usage for a mobile user.