Building sensor networks poses challenges of secure routing, node authentication, data integrity, data confidentiality and access control that are faced in conventional wireless and wired networks as well. In this paper, we argue that the conventional view of security based on cryptography and authentication alone is not sufficient for the unique characteristics and novel misbehaviors encountered in sensor networks. Fundamental to this is the observation that sensor network applications are based on collective interaction between a large numbers of nodes, which do collaborative data gathering, collective data/information processing, and multi-hop data delivery. This decentralized in-network decision-making, which relies on the inherent trust among the sensor nodes, can be abused by adversaries to carry out security breaches. An adversary can potentially insert bogus data to mislead the whole network! Cryptographic mechanisms alone cannot be used to solve this problem as adversarial or faulty sensor nodes can use valid cryptographic keys to authenticate bogus data.

We highlight some scenarios where solely using cryptography fails. On the basis of these observations, we motivate the need of integrating tools from different domains such as economics, statistics and data analysis with cryptography to facilitate the development of high integrity sensor networks. Following this approach, we introduce a reputation-based framework that provides a unified solution for countering several types of malicious/non-malicious misbehavior in sensor networks.