Indistinguishability under Adaptive Chosen Ciphertext Attack, IND-CCA2

Ciphertext is the result of text (plaintext) that has been encrypted using an algorithm, called a cipher. Cryptanalysis looks into methods of obtaining the meaning of encrypted information, and use one or more attack methods to crack the cipher, depending on what information is available and what type of cipher is being analysed.

Ciphertext attack methods include ciphertext-only; known-plaintext; chosen-plaintext; chosen-ciphertext; related-key; each method determines availablity of certain information such as plaintexts, ciphertexts and keys.

With a chosen-ciphertext attack (CCA) the attacker can enter one or more known ciphertexts of their own choosing into the target system and obtain the resulting plaintexts. Chosen-ciphertext attacks, like other attacks, may be adaptive or non-adaptive. In a non-adaptive attack, the attacker chooses a ciphertext to decrypt in advance. In an adaptive chosen-ciphertext attack, the attacker uses the result of prior decryptions to influence their choice of additional ciphertexts. A non-adaptive chosen-ciphertext attack is abbreviated as CCA1. An adaptive chosen-ciphertext attack is abbreviated as CCA2.

Indistinguishability under Adaptive Chosen Ciphertext Attack, IND-CCA2.