Cipher-Cracking Methods

Systematically trying every possible key until a decrypted output makes sense.

(Exhaustive Search / Brute Force) – “Try all combinations.” If question mentions trying many keys until one works, it’s brute force; mitigated by long key lengths.

Attacker knows some plaintext and corresponding ciphertext and uses those pairs to deduce the key or reveal more plaintext.

(Known-Plaintext Attack) – If the attacker already knows parts of the message and uses that to crack other parts, it’s this attack.

Attacker intercepts communication and impersonates each endpoint to the other, relaying and potentially altering messages.

(Man-in-the-Middle / MITM) – “Sits between both parties.” Look for interception + impersonation clues.

Attacker sends chosen ciphertexts to a system and analyzes the decrypted responses to deduce keys or plaintexts.

(Chosen-Ciphertext Attack / CCA) – If attacker can request decryptions of attacker-chosen inputs, think CCA (very powerful).

Any attack in which the adversary injects, inserts, or modifies messages in-transit.

(Active Attack) – “Not just listening; modifying.” If messages are altered or spoofed, it’s active.

Attacker re-sends a valid previously captured message to cause the system to repeat an action.

(Replay Attack) – “Play it again.” Use nonces, timestamps, or sequence numbers to prevent.

Attacker splices pieces of different encrypted messages to form a new message that can trick the receiver.

(Cut-and-Paste Attack) – “Mix-and-match ciphertext parts.” Look for message fragment reuse or lack of binding/integrity.