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 behaviour of the sensor networks. To offer 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.