Key Levels and Securing Key Predistribution against Node Captures

We consider key predistribution schemes deployed for securing communication in ad hoc networks of tiny devices. As node captures are inevitable in these networks and the devices are likely non tamper-proof, an adversary can collect the keys and decrypt some transmissions. We propose and analyze key levels technique that can be used on top of most key predistribution schemes in order to reduce chances of an adversary. The modification does not increase the number of keys loaded into a device, while it increases the computational cost in an insignificant way. Also, it composes well into a framework of adaptive key management allowing to refresh the keys without causing incompatibility problems with the devices holding the old keys. Finally, we show how to reduce the number of keys in a device for random key predistribution by an appropriate construction of the pool of keys.