Question: What is a prerequisite for a Network Application Function (NAF) to securely communicate with a User Equipment (UE) after bootstrapping, assuming no prior security association exists?
Option 1: The NAF must share a pre-existing secret key with the UE.
Option 2: The NAF must acquire shared key material established between the UE and the Bootstrapping Server Function (BSF) during the application-specific protocol run.
Option 3: The UE and NAF must both support the same version of the Transport Layer Security (TLS) protocol.
Option 4: The NAF needs to initiate a new authentication process with the UE using SMS-based One-Time Passwords.
Explanation: According to the Generic Authentication Architecture (GAA) and Generic Bootstrapping Architecture (GBA) principles, for a NAF to communicate securely with a UE without a prior security association, it must obtain the shared key material that was generated during the mutual authentication between the UE and the BSF. This ensures secure communication based on session keys derived from this shared material, facilitating application-specific protocols without requiring pre-existing secrets between the UE and NAF.