Question: In a 3GPP Network Domain Security (NDS) context, what is the requirement for using the NULL authentication algorithm with ESP to provide security services?
Option 1: The NULL authentication algorithm can be used as a fallback when other algorithms fail.
Option 2: It is always allowed for use in scenarios requiring only data confidentiality.
Option 3: It is explicitly not allowed unless an authenticated encryption algorithm is used concurrently.
Option 4: Its use is mandatory for all integrity and anti-replay services.
Explanation: This answer reflects the importance of maintaining integrity, data origin authentication, and anti-replay services in NDS. By disallowing the NULL authentication algorithm (except when paired with an authenticated encryption algorithm), the network ensures that these critical security services are always provided, thereby protecting against various forms of attacks and ensuring the trustworthiness of the data transmitted.