Question: What is the primary purpose of the `f1*` message authentication code (MAC) function in the context of ISIM application, as defined in telecom standards?
Option 1: To ensure mutual secrecy between `f1*` and other functions (`f1`, `f2`, `f3`, `f4`, `f5`) so that no valuable information can be inferred about one from the others.
Option 2: To generate a key for encrypting user data in IP Multimedia Services.
Option 3: To compute the Authentication Key (AK) used in wireless network access.
Option 4: To verify the integrity of signaling messages between the User Equipment (UE) and the Network.
Explanation: The correct answer is Option 1 because, as defined, `f1*` has a specific property that ensures no valuable information can be inferred about the function values of `f1` (and vice versa for other functions like `f2`, `f3`, `f4`, `f5`). This mutual secrecy is crucial for enhancing security in telecom applications, preventing potential attacks based on deducing one function's output from another.