The importance of IT security is growing in recent years in all domains of daily life, economy and public administration. Also for Global Navigation Satellite Systems (GNSS) IT security is of high importance. Although IT security has to be ensured within the complete GNSS architecture (including space segment, ground segment and user segment), the ground segment, as the central element of the overall-system, plays a predominant role from an IT security perspective. Within the ground system (similar to other complex IT infrastructures), internal procedures and data, as well as different interfaces between various sites have to be protected w.r.t. confidentiality, integrity and availability.