Chosen-plaintext attack

A chosen-plaintext attack (CPA) is an attack model for cryptanalysis which presumes that the attacker can obtain the ciphertexts for arbitrary plaintexts. The goal of the attack is to gain information that reduces the security of the encryption scheme.

Immunity to a chosen-plaintext attack is called ciphertext indistinguishability under chosen-plaintext attack (IND-CPA). With an IND-CPA property, the cryptographic scheme is resistant to an attacker that has access to the encryption oracle (e.g., the encryption device) itself. This property is equivalent to the semantic security under CPA (inability of the adversary to gain even partial information about the plaintext from observing the ciphertext). A similar (but stronger) property of indistinguishability under a chosen-ciphertext attack (IND-CCA) reflects the resistance to adversary having access to a decryptor.'

A deterministic block cipher scheme (like electronic codebook) does not possess the IND-CPA, as it will encrypt the plaintext with repeating blocks into ciphertext that will be easily recognizable because its blocks are repeated as well.