Chapter 9 Secrecy Capacity of Diffusion-Based Molecular Communication Systems Lorenzo Mucchi, Alessio Martinelli, Stefano Caputo, Sara Jayousi, and Massimiliano Pierobon 9.1 Introduction Molecular communication (MC) is a recent inter-disciplinary research topic between telecommunications, computer science, and biology [1]. The basic concept under this research area is that in biological systems, which include the human body, the transmitters and receivers communicate each other by using chemical signals or molecules. Molecular communication is seen by telecommunication engineers as a new paradigm where the information flows through chemical reactions and molecules transportation, as opposed to radio or optical signals. For biologists, MC is an abstraction of how biological cells and their components communicate. During the last decade, researchers devoted a lot of efforts in investigating and developing MC-based nano-(bio)-devices and nano-(bio)-networks, and MC is now considered a future (potentially disruptive) communication technology. Communications at molecular/nano-scale level have very different rules and objectives compared to the traditional radio communications. Healthcare is one of the most promising application fields of MC [2]. In particular, MC for health studies how biological and artificial components (nano- sensors, nano-reactors) communicate with each other using molecules. The impacts of this research study could enable a wide number of future applications such as lab-on-a-chip, drug/DNA delivery systems, and human body monitoring using L. Mucchi () · A. Martinelli · S. Caputo · S. Jayousi Department of Information Engineering, University of Florence, Firenze, Italy e-mail: lorenzo.mucchi@unifi.it M. Pierobon Department of Computer Science & Engineering, University of Nebraska-Lincoln, Lincoln, NE, USA e-mail: pierobon@cse.unl.edu © Springer Nature Switzerland AG 2020 C. Sugimoto et al. (eds.), 13th EAI International Conference on Body Area Networks, EAI/Springer Innovations in Communication and Computing, https://doi.org/10.1007/978-3-030-29897-5_9 103