Trust plays an essential role in many types of systems and applications ranging from peer-to-peer computing, fi ltering of information on the web, and recommendation systems to many branches of social networks and e-commerce. Trust is bound to achieve even higher levels of importance because of its increasing use in data centers, mobile systems, and embedded sensing. In mobile systems, due to energy and power restrictions, in many situations it is advantageous to delegate computation to desktop systems, clusters, or data centers. Finally and maybe most importantly, telehealthcare raises the importance of trust to an even higher level. For example, when a doctor wants to conduct gait diagnostics on a patient who has been wearing medical smart shoes equipped

with multiple pressure sensors and a mote capable of wireless transmission, it is crucial that both he and the patient are convinced that the received pressure or other readings are actually from the deployed sensors, that the sensors have not been repositioned, and that the timestamp associated with the data is correct. Without this trust the data is of little value.