(a) Explain what a brute force attack is in the context of encryption. [2] (b) A symmetric encryption key is 8 bits long. Calculate the number of possible k...

(a) A brute force attack is a method of attempting to break encryption by systematically trying every possible key in sequence. [1] The attacker uses software to generate and test each key against the ciphertext until the correct one is found, producing meaningful plaintext. It is essentially a trial-and-error approach that guarantees success given enough time. [1]

(b) An 8-bit key means each bit can be either 0 or 1, giving:

\( 2^8 = 256 \) possible keys [1]

This is a very small key space, meaning a computer could try all 256 keys almost instantly.

(c) Modern encryption uses key lengths of 128 bits or more because this creates an astronomically large key space. A 128-bit key provides \( 2^{128} \approx 3.4 \times 10^{38} \) possible combinations. [1] Even the fastest supercomputers would need billions of years to try every combination, making brute force attacks computationally infeasible. [1]

(d) Two methods other than brute force that attackers might use: [2]

1. Social engineering: manipulating or deceiving a person into revealing the encryption key, password, or other sensitive information. [1]
2. Dictionary attack: trying a list of commonly used passwords and words rather than every possible combination, exploiting the tendency for people to choose predictable passwords. [1]

(e) One protective measure is account lockout: the system locks the account after a set number of failed login attempts (for example, 5 incorrect passwords). [1] This prevents an attacker from rapidly trying thousands of passwords because the account becomes inaccessible after a few failures.