Question: To prevent a bidding down attack in Generic Bootstrapping Architecture (GBA), what is the requirement for a GBA-enabled terminal that supports SIM-based 2G GBA if a USIM/ISIM is available?
Option 1: The terminal may choose between SIM-based 2G GBA and USIM/ISIM-based 3G GBA.
Option 2: The terminal must only use SIM-based 2G GBA for all authentication processes.
Option 3: The terminal must use the USIM/ISIM-based 3G GBA, as it is more secure than SIM-based 2G GBA.
Option 4: The terminal can ignore the presence of a USIM/ISIM and continue using SIM-based 2G GBA.
Explanation: To prevent a bidding down attack (where an attacker forces the use of a less secure protocol), the terminal must utilize the more secure option when available. Since USIM/ISIM-based 3G GBA is considered more secure than SIM-based 2G GBA, especially in the context of preventing such attacks, the terminal is required to use it when a USIM/ISIM is present. This ensures that the authentication process does not get downgraded to a less secure method.