A method, device, and service means for authenticating a client for services to be provided by a service provider agent service

It is proposed a method of authenticating a client for services to be provided by a service agent service. The method includes the steps of authenticating a client as a member of a particular group of customers to the service agent by means of a first of the specific customer group associated group signature for the detection of the client's entitlement to receive a service, requesting the service by the authenticated client at the service agent and the client authenticating as a member of the particular group of customers by means of a second one of the specific customer group associated group signature for the detection of the client's consent for a billing process for billing of the requested service in the accounting center. The method allows the safe use of the service while preserving the anonymity of the customers. Furthermore, an apparatus for implementing the method as well as a service agent are proposed.