Abstract. Current challenges on the markets cause companies to interact with one another and strive after becoming members of virtual organizations assuming that in doing so they can achieve sustainable competitiveness and remain successful despite increased competition. This new openness has strong implications and poses intense demands on organizations’ security systems. In this paper we present architectural considerations and our concept of a security infrastructure to cope with these challenges. The presented approach aims at minimizing the leadtime before usage of external services can start by employing a security intermediary for mediation purposes.