A specially noted variant of the chosen-ciphertext attack is the `` lunchtime '' or `` midnight '' attack , in which an attacker may make adaptive chosen-ciphertext queries but only up until a certain point , after which the attacker must demonstrate some improved ability to attack the system . A specially noted variant of the chosen-ciphertext attack is the `` lunchtime '' , `` midnight '' , or `` indifferent '' attack , in which an attacker may make adaptive chosen-ciphertext queries but only up until a certain point , after which the attacker must demonstrate some improved ability to attack the system .