Secrecy Capacity of Diffusion-based Molecular Communication Systems

Molecular Communication (MC) is a new communication paradigm where, dierently from the radio or optical communication, the information ow is based on the exchange of molecules. The impli- cit biocompatibility and nanoscale feasibility of MC make it a promising communication technology for health applications, from disease detection to drug in-body delivery. Much attention has been paid to MC in the last decade in investigating the fundamentals of information theory app- lied to biochemical reactions, while considerations on security have been very limited. This paper provides a closed-form expression for the se- crecy capacity of an MC system based on the free diusion of molecules, which is of primary importance to understand the security robustness of the MC paradigm. On the basis of this expression, derived through physical-layer-security tools from information theory, numerical results are presented to study the dependence of the secrecy capacity on the average thermodynamic power, the eavesdropper's distance, the trans- mit bandwidth, and the receiver radius. A secrecy map is also presented, which shows the secure and unsecure areas around the legitimate trans- mitter.