Distributed systems are paramount in our increasingly interconnected world, as they provide the backbone for numerous industries and applications. Across domains such as cyber physical systems, cloud computing and more, distributed systems empower the seamless functioning of complex technologies, making them an essential component in today's digital landscape. Our research develops novel techniques to ensure security at the core of systems. Hence, we prioritise security and integrate it seamlessly into the system design process, ensuring robust protection from potential threats. We go beyond conventional measures by employing and advancing practical formal verification techniques specifically tailored to verify the security of new and existing systems.