Is there a relation between passive/active attacks and IND-CPA/IND-CCA? I've seen some papers drawing a connection between IND-CPA and passive attacks and IND-CCA and active attacks. Can someone explain how IND-CPA relates to passive attacks and IND-CCA relates to active attacks if this is indeed the case?
The most recent example of such a paper that I can recall is this: https://eprint.iacr.org/2020/1533
Another example is this excerpt from the preface of Introduction to Modern Cryptography, 3rd edition (http://www.cs.umd.edu/~jkatz/imc.html):
&quot;We have divided our treatment of symmetric-key encryption into two parts:   Chapter 3 deals with security against “passive” attacks (i.e., CPA-security), while Chapter 5 addresses “active” attacks (i.e., CCA-security and authenticated encryption).&quot;
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.