ITPEC FE Subject A April 2024 Question 27

Brute force attack on symmetric encryption — tests all possible keys sequentially until the correct one is found.

Brute force requires a known plaintext-ciphertext pair. The attacker encrypts the plaintext with every possible key and checks if the result matches the ciphertext — no cryptographic insight needed, just exhaustive search.

Why not others:
- (a) Observing ciphertext changes when plaintext is altered → differential cryptanalysis (exploits differences, not exhaustive search)
- (c) Using algebraic relationships between plaintext, ciphertext, and key → algebraic attack
- (d) Using statistical correlation between parts of plaintext and ciphertext → linear cryptanalysis

Key rule: Brute force = try every key one by one; no pattern or math exploited — pure exhaustion.

AI-generated — may contain errors