A class of cryptanalytic methods where the analyst can choose an unlimited number of plaintexts and obtain the resulting ciphertexts from a cryptosystem, and from there deduce the key to the system. Compare known plaintext attack.

An adaptive chosen plaintext attack means that the cryptanalyst can choose plaintexts based on the results of his or her previous choices.

Differential cryptanalysis and some of the more specialized attacks on ciphers fall into this category, and can typically be very powerful.