The paper describes an approach for the integration of transparent security mechanisms into de-centralized mobile application scenarios. This becomes necessary as the communication among various devices migrates to wireless technologies at a progressive rate, finally leading to pervasive computing scenarios. Our result is a modular and heterogeneous architecture based on a high-capacity middleware. In this regard, the web services technology is a guarantor for modularity as well as flexibility. It allows the integration of special tasks applying high security and mobility on different layers. This paper describes basic technologies used in such a system as well as selected aspects of a realized prototype.