Which attack involves the attacker choosing plaintexts to be encrypted and observing the resulting ciphertexts?

• A. Chosen-plaintext attack
• B. Attacker modifies ciphertext
• C. Attacker uses hashed outputs
• D. Attacker performs public-key cryptanalysis

Answer: (A)

This question is about a chosen-plaintext attack. In this scenario, the attacker can select specific plaintexts and request their encryption to see the resulting ciphertexts. By controlling the inputs to the encryption process and observing the outputs, the attacker probes how the algorithm maps plaintexts to ciphertexts under the secret key, looking for patterns or weaknesses to exploit. This is a standard way to test whether an encryption scheme remains secure even when the attacker can force certain messages to be encrypted.

The other options describe different scenarios. Modifying ciphertext refers to tampering with or altering ciphertext after encryption, which is about ciphertext integrity and malleability rather than choosing plaintexts. Using hashed outputs relates to hash functions, not the encryption process itself. Public-key cryptanalysis is a broad activity aimed at breaking public-key systems in general and does not specify the attacker’s ability to choose plaintexts for encryption.