FIELD: radio engineering, communication.
SUBSTANCE: invention relates to communication engineering. The key derivation method comprises steps of: receiving, by a mobility management entity (MME), a "Handover Required" message from a base station (BS); deriving, by the MME, a user equipment (UE) key in the target Universal Terrestrial Radio Access Network (UTRAN) according to a Key Derivation Function (KDF), a root key, and the NAS downlink COUNT value; and sending, by the MME, the current NAS downlink COUNT value to the UE, and adding, by the MME, a certain value to the current NAS downlink COUNT value.
EFFECT: improved network security.
11 cl, 14 dwg
