1. A user equipment for updating a key, comprising: a receiver, configured to receive, from an evolved NodeB (eNB), an intra-cell handover command which is configured to instruct the user equipment to use air-interface keys; wherein the air-interface keys have been updated by the eNB based on a new key K eNB ; wherein the eNB is informed by a Mobility Management Entity (MME) of the new key K eNB generated during a key update procedure; wherein the key update procedure was initiated by the MME when a pre-defined condition is met.