A thief walks up to an electronic lock with a 10-digit keypad and he notices that all but three of the keys are covered in dust while the 2, 4, 6, and 8 keys show considerable wear. He thus can safely assume that the 4-digit code that opens the door must be made up of these numbers in some order. What is the worst case number of combinations he must now test to try open this using a brute-force attack?

The answer is 256 combinations

Explanation:

A brute force intrusion seems to be an action that breaks the credentials, or just to locate a secret page, or perhaps to identify that combination required for encode the file, and use the trials and error technique and ultimately trying to determine correctly.

Given that, for each of the four digits, there are the following possibilities occur that is 2, 4, 6, 8 .

Therefore, there are the following possible combinations that are

Which indicates that there are 256 combinations under the worst scenario