When installing and maintaining a wireless sensor network in a medical or factory environment, distribution of keying material to sensor nodes (18) is performed by a key material box (KMB) (12), such as a smartcard or the like. The KMB (12) has a random seed stored to it during manufacture, and upon activation performs an authentication protocol with a sensor node (18) to be updated or installed. The KMB (12) receives node identification information, which is used in conjunction with the random seed to generate keying material for the node (18). The KMB (12) then encrypts the keying material for transmission to the node (18), and transmits over a wired or wireless communication link in a secure manner. The node (18) sends an acknowledgement message back the KMB (12), which then updates the node s status in look-up tables stored in the KMB (12).