A ( full ) adaptive chosen-ciphertext attack is an attack in which ciphertexts may be chosen adaptively before and after a challenge ciphertext is given to the attacker , with ONE condition that the challenge ciphertext may not itself be queried . A ( full ) adaptive chosen-ciphertext attack is an attack in which ciphertexts may be chosen adaptively before and after a challenge ciphertext is given to the attacker , with only the stipulation that the challenge ciphertext may not itself be queried .