Internet of Things (IoT), also referred to as the Internet of Objects, is envisioned as a holistic and transformative approach for providing numerous services. The rapid development of various communication protocols and miniaturization of transceivers along with recent advances in sensing technologies offer the opportunity to transform isolated devices into communicating smart things. Smart things, that can sense, store, and even process electrical, thermal, optical, chemical, and other signals to extract user-/environment-related information, have enabled services only limited by human imagination.Despite picturesque promises of IoT-enabled systems, the integration of smart things into the standard Internet introduces several security challenges because the majority of Internet technologies, communication protocols, and sensors were not designed to support IoT. Several recent research studies have demonstrated that launching security/privacy attacks against IoT-enabled systems, in particular wearable medical sensor (WMS)-based systems, may lead to catastrophic situations and life-threatening conditions. Therefore, security threats and privacy concerns in the IoT domain need to be proactively studied and aggressively addressed. In this thesis, we tackle several domain-specific security/privacy challenges associated with IoTenabled systems.We first target health monitoring systems that are one of the most widely-used types of IoT-enabled systems. We discuss and evaluate several energy-efficient schemes and algorithms, which significantly reduce total energy consumption of different implantable and wearable medical devices (IWMDs). The proposed schemes make continuous long-term health monitoring feasible while providing spare energy needed for data encryption. Furthermore, we present two energy-efficient protocols for implantable medical devices (IMDs), which are essential for data encryption: (i) a secure wakeup protocol I have had the honor and privilege to work under the supervision of Prof. Niraj K. Jha. who helped me take the first steps as a researcher. His guidance and support have helped me with academic research and writing from the first day of the Ph.D. program and have been very beneficial in shaping my Ph.D work. Apart from his immense wisdom and insight, his enthusiasm to explore new research directions and novel ideas has been a constant source of inspiration to me. His patience, kindness, understanding, and empathy towards his students are truly admirable. He has been extremely caring during my days of struggle. Although I have immensely benefited from his technical expertise, I still have so much to learn from his superior discipline and kind disposition. I also received much advice and guidance from Profs. Anand Raghunathan, Susmita Sur-Kolay, and Mehran Mozaffari-Kermani. Discussion with them were always an exceptional source of new ideas. Without their continuous support, encouragement, and inspiration, preparing this thesis would not have been feasible. I am deeply grateful for the guidance of...