Sensors and actuators offer services in service-centric sensor networks, e.g. they provide information about the temperature at a certain location. Those services are building blocks for the overall behavior of the sensor networks. To offer a dynamic composition of services and to make services available for every node in the network, a way to securely store and retrieve information about available services of the network is necessary. The paper presents Secure Content Addressable Network (SCAN) which is a distributed approach to a secure service directory for service-centric sensor networks.