In a chosen-ciphertext attack [102], an attacker has access to a decryption oracle that allows decrypting any chosen ciphertext (except the one that the attacker attempts to reveal). In the general setting, the attacker has to choose all cipher texts in advance before querying the oracle.

In the adaptive chosen-ciphertext attack, formalized by Rackoff and Simon (1991), one can adapt this selection depending on the interaction with the oracle. An especially 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.