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This question already has an answer here:

CPA attack means the attacker can send in his own plaintext to the oracle and receives some sort of ciphertext back.

CCA attack means the attacker can send in his own ciphertext to the oracle and return some sort of plaintext back.

When we talk about CPA and CCA secure, what exactly are we referring? All this time I just think of it as " if it's CPA secure, then the attacker cannot perform a CPA, which means when the attacker sends in his own plaintext he will not receive some sort of ciphertext back"

That makes logical sense to me, but I really don't feel like I am understanding CPA/CCA secure correctly.

I thought the whole point is so that the attacker can send in whatever ciphertext / plaintext he desires, the attacker will get something back, and the system will not leak information. Does that mean that I can also think of it as " the attacker can send in whatever cipher/plaintext he wants, but he will not receive informative outputs" ?

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marked as duplicate by otus, K.G., Community Oct 5 '15 at 21:23

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    $\begingroup$ Does this help? $\endgroup$ – SEJPM Oct 5 '15 at 19:58
  • $\begingroup$ That was a beautiful written response, definitely helped $\endgroup$ – user3277633 Oct 5 '15 at 20:23

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