Question: What happens to a corresponding `Ks_int_NAF` key in the USIM's EFGBANL record when its associated MUK (identified by MUK ID) is deleted in the context of MBMS security?
Option 1: The `Ks_int_NAF` key is updated with new security parameters.
Option 2: The `Ks_int_NAF` key remains unchanged, as it's not directly linked to MUK deletion.
Option 3: The `Ks_int_NAF` key is deleted, and its record in EFGBANL is set to 'FF'.
Option 4: The USIM returns an error status for attempting to modify a `Ks_int_NAF` key.
Explanation: In the context of MBMS security on a USIM, when a MUK (identified by its MUK ID) is deleted, any corresponding security elements that rely on it are also removed for consistency and security. Specifically, if a `Ks_int_NAF` key with the same NAF_ID as the MUK being deleted exists, it is deleted to prevent unauthorized access or misuse of outdated security parameters. The record in EFGBANL is then set to 'FF' to indicate its deletion, maintaining the integrity and synchronization of security settings within the USIM.