The disclosure relates to a security method and system in a telecommunications network comprising a radio access network system and a core network system. The radio access network system is configured to provide a wireless radio interface for at least one user device, wherein a shared secret key is stored in both the user device and the core network system. At least one vector is received from the core network system comprising one or more values derived from the shared secret key. At least one of an authentication procedure and a key agreement procedure is performed in the radio access network system for the user device over the wireless radio interface using the one or more values of the received vector for establishing a connection between the user device and the radio access network system.