Attacker has access to both the plaintext and its corresponding ciphertext. This describes which attack?

• A. Known-plaintext attack
• B. Attacker encrypts chosen plaintext
• C. Attacker intercepts while message is in transit
• D. Attacker finds the key by guessing

Answer: (A)

Having access to both the original message and its encrypted form is a known-plaintext attack. In this scenario, the attacker uses the known pairs of plaintext and ciphertext to infer information about the secret key or weaknesses in the cipher, with the goal of decrypting other messages that use the same key. This distinguishes it from scenarios where the attacker can choose plaintexts to obtain ciphertexts, or only observes ciphertexts without knowing the corresponding plaintext, or simply tries to guess the key without leveraging known mappings. The defining feature is leveraging known plaintext–ciphertext pairs to break or bypass the encryption.