Question: Upon successful integrity protection check of the SecurityModeCommand message, what actions does the UE take regarding SRB (Signaling Radio Bearer) security configuration?
Option 1: Apply SRB integrity protection immediately with the KRRCint key, and apply SRB ciphering after completing the procedure with the KRRCenc key.
Option 2: Apply both SRB integrity protection and SRB ciphering immediately with their respective keys (KRRCint and KRRCenc).
Option 3: Delay applying both SRB integrity protection and SRB ciphering until the next RRC connection re-establishment.
Option 4: Only apply SRB integrity protection without configuring SRB ciphering.
Explanation: Upon passing the integrity check, the UE configures lower layers to apply SRB integrity protection immediately using the KRRCint key for all subsequent messages (including the SecurityModeComplete message which is an exception for ciphering). Meanwhile, SRB ciphering using the KRRCenc key is applied after completing the procedure, excluding the SecurityModeComplete message.