In this paper we re-examine the attacking scenario about wireless sensor networks. It is generally assumed that the adversary picks up all radio communications of sensor nodes without any loss and stores the eavesdropped messages for later use. We suggest that in some situations the adversary may not be able to pick up all radio communications of sensor nodes. Therefore, we propose the storage-bounded adversary model for wireless sensor networks, in which the adversary's storage is bounded. We propose two key establishment schemes for establishing shared keys for neighboring sensor nodes in the storage-bounded adversary model. The first scheme needs special beacon nodes for broadcasting random bits. In the second scheme, some sensor nodes play the role of beacon nodes. Our results are theoretical in some sense. Nevertheless, we can adjust them for realistic consideration.