PART III Security for Sensor Networks schemes to ensure sensor data integrity, avail- ability, and confidentiality in WSNs under hos- tile situations. In particular, this chapter discusses two efficient distributed access control methods, namely uni-access query and multi-access query. The uni-access query method uses symmetric cryptographic operations that allow an autho- rized user to access sensory data in a node directly and also to delegate to others without going through the base station. The multi-access query method, on the other hand, applies public key cryptography to support a user access the data on many sensor nodes via a single query, thus reduc- ing the communication overhead significantly. Chapter 10 titled "Defending against Physi- cal Attacks in Wireless Sensor Networks" stud- ies challenges associated with defending WSNs against physical attacks, defined as those that physically destroy sensors or otherwise render them non-functional, and it describes effective 225 compromises them. The attacker could also move them to multiple locations to evade detection. In the widespread attack, on the other hand, an attacker can generate many replicas of a few compromised nodes and widely disseminate them over the network. To stop these attacks as soon as possible, this chapter first proposes a reputation- based node compromise detection scheme and a scheme for distributed detection of mobile mali- cious node attacks in static sensor networks. This chapter also proposes a replica detection scheme in static and mobile sensor networks. REFERENCES [1] L. Eschenauer, V.D. Gligor, A key-management scheme for distributed sensor networks, Proceedings of the Ninth ACM Conference on Computer and Communications Security (CCS '02), November 2002. [2] D. Liu, P. Ning, Establishing pairwise keys in