Topology-based Secret Key Generation for Underwater Acoustic Networks

We propose a method to let a source and a destination agree on a key that remains secret to a potential eavesdropper in an underwater acoustic network (UWAN). We generate the key from the propagation delay measured over a set of multihop routes: this harvests the randomness in the UWAN topology and turns the slow sound propagation in the water into an advantage for the key agreement protocol. Our scheme relies on a route discovery handshake. During this process, all intermediate relays accumulate message processing delays, so that both the source and the destination can compute the actual propagation delays along each route, and map this information to a string of bits. Finally, via a secret key agreement from the information-theoretic security framework, we obtain an equal set of bits at the source and destination, which is provably secret to a potential eavesdropper located away from both nodes. Our simulation results show that, even for small UWANs of 4 nodes, we obtain 11 secret bits per explored topology, and that the protocol is insensitive to an average node speed of up to 0.5 m/s.