Section: 6.1.1.3 Granularity of anchor key binding to serving network
Content: The primary authentication and key agreement procedures shall bind the KSEAF to the serving network. The binding to the serving network prevents one serving network from claiming to be a different serving network, and thus provides implicit serving network authentication to the UE. This implicit serving network authentication shall be provided to the UE irrespective of the access network technology, so it applies to both 3GPP and non-3GPP access networks. Furthermore, the anchor key provided to the serving network shall also be specific to the authentication having taken place between the UE and a 5G core network, i.e. the KSEAF shall be cryptographically separate from the key KASME delivered from the home network to the serving network in earlier mobile network generations. The anchor key binding shall be achieved by including a parameter called "serving network name" into the chain of key derivations that leads from the long-term subscriber key to the anchor key. The value of serving network name is defined in sub-clause 6.1.1.4 of the present document. The chain of key derivations that leads from the long-term subscriber key to the anchor key is specified in sub-clause 6.1.3 of the present document for each (class) of authentication methods. The key derivation rules are specified in Annex A. NOTE: No parameter like 'access network type' is used for anchor key binding as 5G core procedures are supposed to be access network agnostic.