2.2. Authenticated Decryption

2.2. Authenticated Decryption

The authenticated decryption operation has four inputs: K, N, A, and C, as defined above. It has only a single output, either a plaintext value P or a special symbol FAIL that indicates that the inputs are not authentic. A ciphertext C, a nonce N, and associated data A are authentic for key K when C is generated by the encrypt operation with inputs K, N, P, and A, for some values of N, P, and A. The authenticated decrypt operation will, with high probability, return FAIL whenever the inputs N, P, and A were crafted by a nonce-respecting adversary that does not know the secret key (assuming that the AEAD algorithm is secure).