A well-known and established power system protection system is line current differential protection. In order to set up such a protection system, communication between the protection relays, i.e. the protection interface, is required. This protection interface must work reliably under normal operation conditions and must contain security measures to be protected against malicious, intentional attacks. State-of-the-art technologies are cost-intensive, which creates an obstacle when using them. The aim of this dissertation is the realization of a protection interface for the line current differential protection system over existing communication networks, which are less expensive to implement and/or already exist. For this purpose, a communication concept needs to be developed so that these networks can also be used reliably for the line current differential protection. The proposed concept consists of two parts: channel-based clock synchronization and a particularly designed security concept. This allows the system to operate properly and protect the system from attackers and prevents a malfunction of the protection system as much as practically possible. The developed security concept is based on a threat analysis, consisting of the established encryption protocol IPsec and a method which detects asymmetric delay attacks. An investigation of the influence of the security measures on the protective function is performed. With this concept, the protection function is not affected as long as the necessary CPU performance and transmission bandwidth are available. As the final verification of the overall concept, an end-to-end verification of the line current differential protection system is performed by using different operating conditions. This verification shows flawless functionality of the overall concept.