In a brute-force attack, on average, how many of all possible keys must be tried to achieve success?

• A. All possible keys
• B. A quarter of all possible keys
• C. Half of all possible keys
• D. A specific number of keys

Answer: (C)

In a brute-force attack, the objective is to systematically attempt every combination of possible keys until the correct one is found. Given this method, we can analyze the expectations associated with key attempts.

When dealing with a set of possible keys, if the key space consists of 'N' total keys, the average number of keys that must be tried to succeed would typically be calculated as follows. On average, the correct key will be found roughly halfway through the total number of options. This means that, statistically, it will take about half of all possible keys to find the correct one due to the nature of random chance and distribution across the entire key space.

This reasoning highlights why the average number of keys that must be attempted is half of all possible keys.