Question: Under what condition(s) may a UE (User Equipment) store its full native EPS NAS (Evolved Packet System Non-Access Stratum) security context on the USIM (Universal Subscriber Identity Module) or in non-volatile ME (Mobile Equipment) memory?
Option 1: During every successful EPS AKA (Authentication and Key Agreement) run.
Option 2: Only when transitioning to EMM-DEREGISTERED state or if an attempt to transition away from this state fails.
Option 3: Whenever the UE is powered on and a UICC (Universal Integrated Circuit Card) is present.
Option 4: After every handover to E-UTRAN (Evolved Universal Terrestrial Radio Access Network).
Explanation: According to the security architecture for EPS, the full native EPS NAS security context (with exceptions like KNASenc and KNASint) is stored on the USIM (if supported) or in the non-volatile memory of the ME specifically during the transition to EMM-DEREGISTERED state or if an attempt to leave this state fails. This ensures secure storage of sensitive information under specific, controlled conditions, maintaining the integrity of the security context.