Question: In the context of 2G Generic Bootstrapping Architecture (GBA), which of the following scenarios could potentially allow an attacker to determine Kc, exploiting a vulnerability in the encryption protocol used between the Mobile Equipment (ME) and the Base Station?
Option 1: When the ME uses A5/3 encryption with fully randomized fillbits.
Option 2: When the attacker forces the use of A5/1 on the ME, especially if the fillbits are not random.
Option 3: When the ME and Base Station negotiate to use GEA2 for encryption.
Option 4: When the network authenticates the ME using GSM MILENAGE algorithms.
Explanation: This is correct because, as explained in the context of 2G GBA security threats, an attacker could determine Kc if they force the use of A5/1 on the ME (using a false base station) and the fillbits are not random. This vulnerability highlights the importance of using secure encryption protocols with randomized elements to prevent such exploits. Options 1 and 3 are incorrect because A5/3 is considered more secure, and there's no mention of GEA2 being vulnerable in this context. Option 4 is also incorrect as GSM MILENAGE algorithms relate to authentication and key generation (A3/A8), not directly to the encryption protocols like A5/1 or GEA.