IND-CCA is definition used in cryptography to describe:

  • indistinguishability under (non-adaptive) chosen ciphertext attack (IND-CCA1), and
  • indistinguishability under adaptive chosen ciphertext attack (IND-CCA2).

There's also a third definition in this relation: indistinguishability under chosen plaintext attack (IND-CPA).

Security under either of these implies security under the previous ones: a scheme which is IND-CCA1 secure is also IND-CPA secure, and a scheme which is IND-CCA2 secure is both IND-CCA1 and IND-CPA secure. Thus, IND-CCA2 is the strongest of the three definitions of security.

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