Secure Code Distribution in Dynamically Programmable Wireless Sensor Networks ; CU-CS-1000-05

For deployed wireless sensor networks, reprogramming sensor nodes through the wireless channel is an important capability. To avoid reprogramming false or viral code images, it is important to make sure that each sensor node can securely receive its code image through the wireless channel. Public key schemes based on elliptic curve cryptography are feasible in wireless sensor networks, yet are still very expensive in terms of memory and CPU consumption. This paper explores hybrid mechanisms that combine the speedy verification of packetized code allowed by hash-based schemes with the strong authenticity provided by a public key scheme. Based on this idea, three schemes for secure code propagation are proposed. The chain based scheme works best when packets are received in the order they are sent with very few losses. The hash tree based scheme allows nodes to authenticate packets and verify their integrity quickly, even when the packets may arrive out of order. Finally, the hybrid scheme combines the advantages of the first two schemes, and further reduces memory consumption and number of public key operations that a node has to perform. Simulation shows that the proposed secure reprogramming schemes add only a modest amount of overhead to a conventional non-secure reprogramming scheme, namely Deluge, and are therefore feasible and practical in a wireless sensor network.