Question: In which security context does the ISIM use the subscriber authentication key K for command execution, specifically to calculate both a cipher key and an integrity key during IMS context establishment?
Option 1: HTTP Digest security context, utilizing IETF guidelines
Option 2: GBA_U security context in Bootstrapping Mode with the BSF
Option 3: IMS AKA security context for authenticating ISIM to its Home Network (HN)
Option 4: Local Key Establishment security context for deriving NAF specific keys
Explanation: The correct answer is Option 3 because, during an IMS AKA security context, the ISIM utilizes the subscriber authentication key K to calculate both a cipher key and an integrity key when establishing an IMS context and receiving a challenge from the IMS.