Question: In the context of key establishment between a Universal Integrated Circuit Card (UICC) and a Terminal for a Ks_local-based application, what triggers the Terminal to initiate a Key Establishment procedure with the UICC?
Option 1: When the Terminal successfully retrieves a valid key Ks_local from its storage for the targeted application.
Option 2: When the Terminal finds that it does not store a valid key Ks_local required for the application, or when the UICC confirms it does not have the required key Ks_local.
Option 3: After every successful communication session between the UICC and the Terminal to update security keys periodically.
Option 4: When the UICC proactively sends a request to the Terminal to establish a new key Ks_local for enhanced security.
Explanation: The correct answer is Option 2 because, according to the key establishment process, the Terminal initiates the Key Establishment procedure in two scenarios: (1) when it doesn't have a valid key Ks_local for the application, and (2) when the UICC responds indicating it also doesn't have the required key Ks_local. This ensures both parties share the same key before proceeding with the application, enhancing security and ensuring synchronization.