Question: In a 5G network, after AS security activation, how are RRC messages on SRB2 protected, and what additional protection is applied by NAS?
Option 1: Only integrity protected by PDCP; no additional NAS protection.
Option 2: Ciphered by PDCP but not integrity protected; NAS applies additional ciphering.
Option 3: Integrity protected and ciphered by PDCP; NAS also applies integrity protection and ciphering.
Option 4: Not protected by PDCP; NAS independently applies both integrity protection and ciphering.
Explanation: Once AS security is activated, all RRC messages on SRB2 are both integrity protected and ciphered by PDCP. Additionally, NAS independently applies its own layer of integrity protection and ciphering to the NAS messages contained within those RRC messages, ensuring dual-layer security for these critical communications in a 5G network.