METHOD FOR HANDLING CIPHER KEY IN MOBILE STATION

摘要

PROBLEM TO BE SOLVED: To handle cipher keys in a mobile station including mobile equipment (ME) and a Universal Subscriber Identity Module (USIM).SOLUTION: A method includes the steps of: obtaining a UMTS cipher key (CK), an integrity key (IK), and a cipher key sequence number (CKSN) from a USIM; deriving a 128-bit cipher key (Kc-128) from the CK and the IK; and storing the Kc-128 and the CKSN in the mobile equipment separately 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. The method is applied to the generation and storage of the 128-bit cipher key for either the packet-switched or circuit-switched domains.