In a method for distributing keys for encrypted data transmission in a sensor network, nodes store a subset of keys from a set of keys. A sink node triggers the key election procedure and sensor nodes choose from a locally broadcasted keyID list, with one key to be stored on each node. All other initially stored keys are subsequently deleted. The process is repeated until the edge of the network is reached. Such key predistribution is suitable for the encryption of reverse multicast traffic to the sink node which is the predominant traffic pattern in wireless sensor networks.