The present disclosure relates to methods and apparatus for flexible, security context management during AMF changes. One aspect of the disclosure is a mechanism for achieving backward security during AMF changes in idle mode. Instead of passing the current NAS key to the target AMF, the source AMF derives a new NAS key, provides the new NAS key to the target AMF, along with a key change indication indicating that the NAS key has changed. The target AMF sends the key change indication to the user equipment.