  As an increasing amount of research is being done on various applications of
sensor networks in adversarial environments, ensuring secure routing becomes of
critical importance for the success of such deployments. The problem of
designing a secure routing protocol for ad hoc networks has been already
addressed, yet, there exists no complete solution that meets the specific
requirements of sensor networks, where nodes are extremely constrained in terms
of both power and computational resources. Thus, we propose a new protocol that
is not built solely around security but also has efficiency and simplicity
among its main goals. We propose the Secure Ad Hoc Efficient Routing protocol
(SAHER) which employs a two-tier architecture based on node clustering. Also,
we combine mechanisms like localscale geographic routing, per-node reputation
tables, credit based alternate route enforcement and cumulative authentication.
Using these techniques we examine ways to efficiently defend against the two
most common network layer attacks: selective packet dropping and message
flooding. Further, we consider join/leave operations which have not yet been
studied in sufficient depth for sensor networks from a security standpoint. We
provide a description of the protocol along with comprehensive experimental
evaluation under different node distributions, different proportions of
non-malicious vs. malicious nodes and different types of activity that
malicious nodes could exhibit.
