Information security for sensors by overwhelming random sequences and permutations

We propose efficient schemes for information-theoretically secure key exchange in the Bounded Storage Model (BSM), where the adversary is assumed to have limited storage. Our schemes generate a secret One Time Pad (OTP) shared by the sender and the receiver, from a large number of public random bits produced by the sender or by an external source. Our schemes initially generate a small number of shared secret bits, using known techniques. We introduce a new method to expand a small number of shared bits to a much longer, shared key. Our schemes are tailored to the requirements of sensor nodes and wireless networks. They are simple, efficient to implement and take advantage of the fact that practical wireless protocols transmit data in frames, unlike previous protocols, which assume access to specific bits in a stream of data. Indeed, our main contribution is twofold. On the one hand, we construct schemes that are attractive in terms of simplicity, computational complexity, number of bits read from the shared random source and expansion factor of the initial key to the final shared key. On the other hand, we show how to transform any existing scheme for key exchange in BSM into a more efficient scheme in the number of bits it reads from the shared source, given that the source is transmitted in frames.