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Key management has two important aspects: key distribution, which describes how to disseminate secret information to the principals so that secure communications can be initiated, and key revocation, which describes how to remove secrets that may have been compromised. Key management in sensor networks face constraints of large scale, lack of a priori information about deployment topology, and limitations of sensor node hardware. While key distribution has been studied extensively in recent works, the problem of key and node revocation in sensor networks has received relatively little attention. Yet, revocation protocols that function correctly in the presence of active adversaries pretending to be legitimate protocol participants via compromised sensor nodes are essential. In their absence, an adversary could take control of the sensor network's operation by using compromised nodes which retain their network connectivity for extended periods of time. In this paper, we present an overview of key-distribution methods in sensor networks and their salient features to provide context for understanding key and node revocation. Then, we define basic properties that distributed sensor-node revocation protocols must satisfy and present a protocol for distributed node revocation that satisfies these properties under general assumptions and a standard attacker model.