  Modern Implantable Medical Devices (IMDs) feature wireless connectivity,
which makes them vulnerable to security attacks. Particular to IMDs is the
battery Denial-of-Service attack whereby attackers aim to fully deplete the
battery by occupying the IMD with continuous authentication requests.
Zero-Power Defense (ZPD) based on energy harvesting is known to be an excellent
protection against these attacks. This paper establishes essential design
specifications for employing ZPD techniques in IMDs, offers a critical review
of ZPD techniques found in literature and, subsequently, gives crucial
recommendations for developing comprehensive ZPD solutions.
