Efficient cellular network security configuration

Security key management is provided between a cellular network and a mobile terminal. The mobile terminal and an authentication management node of the cellular network both store a common security key. A key management message is communicated between the cellular network and the mobile terminal 10. In response to the communication 20, an intermediate security key specific to the mobile terminal is generated 30 using the stored common authentication key . A session security key 40 is generated using the intermediate security key, for securing a communications session between the cellular network and the mobile terminal. Using an intermediate key which is longer lived than a session key increases the time required between rekeying the device. This is especially useful for Machine-Type-Communication (MTC) devices which are typically low-usage, low-power devices. For these devices, frequent updating of a security key may represent a large proportion of the data they communicates and subsequently ...