Today’s power systems are going through a process of decentralization and digitalization that is changing traditional smart grids into Smart Energy Systems. There are several types of communication protocols used for interaction between distributed generation, smart meters, building automation systems, energy storage and demand response events. This process increases efficiency and flexibility and enables a better connection to renewable energy sources; however, it simultaneously makes the system more vulnerable than the classical architecture was. Many communication protocols developed earlier under the criteria of reliability and efficiency now need rigorous cybersecurity requirements. This thesis will analyze the security and efficiency trade-offs of the main communication protocols used at different levels of a Smart Energy System.