Secret Key Extraction using Galvanic Coupling in Wireless Body Area Networks

The evolution of wearable medical devices has made it essential to ensure not only efficient but also secure communication within wireless Body Area Networks (WBANs). Traditional wireless radio frequency transmission methods suffer from limitations in terms of security. Symmetric encryption is recognized to be a solution to provide security to low-resourced on-body devices, but it suffers from the problem of secret key distribution/sharing. Physical-Layer security provides a solution to this issue by using the key agreement method: extracting the key from body signals. Anyway, many body signals are not easy to be extracted or processed. In this context, on-body communication via Galvanic coupling (GC) represents a promising alternative, leveraging the conduction of electrical signals through biological tissues to limit eavesdropping and reduce complexity, including energy consumption. This work proposes an innovative method for secret key extraction based on the reciprocity of GC channels. Two on-body devices can dynamically generate shared cryptographic keys, ensuring a secure communication channel without the need to transmit keys that could be vulnerable to attacks. Through an experimental analysis conducted on human subjects, we demonstrate the feasibility and security of this method, highlighting how the characteristics of a GC-based approach prevent an external attacker from reconstructing the key.