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Key management is a core mechanism to ensure the security of applications and network services in wireless sensor networks. It includes two aspects: key distribution and key revocation. Key distribution has been extensively studied in the context of sensor networks. However, key revocation has received relatively little attention. Existing key revocation schemes can be divided into two categories: centralized key revocation scheme and distributed key revocation scheme. In this paper, we first review and summarize the current key revocation schemes for sensor networks. Then, we present an efficient scheme of removing compromised sensor nodes from wireless sensor networks. Unlike most sensor node removal schemes focusing on removing the compromised keys, the proposed scheme, KeyRev, uses key update techniques to obsolesce the keys owned by the compromised sensor nodes and thus remove the nodes from the network. Our analyses show that the KeyRev scheme is secure inspite of not removing the pre-distributed key materials at com- promised sensor nodes. Simulation results also indicate that the KeyRev scheme is scalable and performs very well compared with other key revocation schemes in wireless sensor networks.