Is there a relation between passive/active attacks and IND-CPA/IND-CCA?
IND-CPA and IND-CCA are formal security models. &quot;Active&quot; and &quot;passive&quot; are informal descriptive terms.
&quot;Passive&quot; usually refers to an adversary who simply observes a system under its normal operation by honest users. &quot;Active&quot; refers to an adversary who &quot;interferes&quot; in some way, causing situations that cannot arise under honest usage, usually by providing &quot;unexpected&quot; or &quot;impossible&quot; cryptographic data.
CPA is a &quot;passive&quot; attack since the adversary just observes honestly generated ciphertexts. The adversary chooses the plaintexts, but that is not considered an &quot;active&quot; attack -- plaintexts themselves are not cryptographic, and the encryption algorithm is still applied honestly to those plaintexts.
CCA is an &quot;active&quot; attack since the adversary can cause maliciously generated ciphertexts to be decrypted. This is something that can never happen under the normal operations of a system by honest users.
The paper that you reference considers itself a &quot;passive&quot; attack because it only involves decrypting ciphertexts that are the result of honestly running (an adversarially chosen sequence of) the encryption scheme's algorithms.