Question: In the primary authentication and key agreement procedure between a UE (User Equipment) and a network, what is the expected outcome when the USIM (Universal Subscriber Identity Module) successfully verifies the freshness of the AV' by accepting the AUTN (Authentication Token)?
Option 1: The USIM discards the RAND (Random Number) and requests a new authentication challenge.
Option 2: The USIM computes a response RES (Response) and returns RES, CK (Cipher Key), IK (Integrity Key) to the ME (Mobile Equipment).
Option 3: The USIM directly establishes encrypted communication with the network without further key exchange.
Option 4: The USIM initiates a secondary authentication procedure for additional security.
Explanation: Upon successful verification of the AUTN, indicating the freshness and validity of the authentication challenge, the USIM proceeds to generate a response (RES) to the challenge. Alongside RES, it also computes and returns the Cipher Key (CK) and Integrity Key (IK) to the Mobile Equipment (ME). These keys are crucial for securing subsequent communications between the UE and the network, ensuring confidentiality (via CK) and integrity (via IK) of the data exchanged. This step is pivotal in establishing a secure connection post-authentication.