We investigate how to build secure yet easy-to-use and cost-effective systems. Our research focuses on areas like improving security usability with contextual data, ensuring privacy in cloud services, and designing secure software-defined networking. We evaluate and optimize mobile and distributed systems to save energy and improve user experience of mobile cloud services and applications like crowdsensing, multimedia streaming, and edge/cloud computing. We also research topics in areas like mobile cloud gaming, internet of things, big data analytics, and verification of distributed systems.