METHOD FOR HANDLING CIPHERING KEYS IN A MOBILE STATION

摘要

Techniques for handling ciphering keys in a mobile station comprising a mobile equipment (ME) and a Universal Subscriber Identity Module (USIM) are disclosed. An example method includes obtaining a UMTS cipher key (CK), integrity key (IK), and ciphering key sequence number (CKSN) from the USIM, deriving a 128-bit ciphering key (Kc-128) from the CK and the IK, and storing the Kc-128 and the CKSN on the mobile equipment, separate from the USIM. The stored CKSN is associated with the stored Kc-128, so that the Kc-128's correspondence to the most current UMTS security context can be tracked. This example method applies to the generation and storage of a 128-bit ciphering key for either the packet-switched or circuit- switched domains. A corresponding user equipment apparatus is also disclosed.