This document contains specifications for a set of ITS station security services required to ensure the authenticity of the source and integrity of information exchanged between trusted entities, i.e.: between devices operated as bounded secured managed entities, i.e. "ITS Station Communication Units" (ITS-SCU) and "ITS station units" (ITS-SU) as specified in ISO 21217; and between ITS-SUs (composed of one or several ITS-SCUs) and external trusted entities such as sensor and control networks. These services include the authentication and secure session establishment which are required to exchange information in a trusted and secure manner. These services are essential for many intelligent transport system (ITS) applications and services, including time-critical safety applications, automated driving, remote management of ITS stations (ISO 24102-2), and roadside/infrastructure-related services.