# IND-CCA2 secure schemes without Plaintext Awareness?

I have been reading up on IND-CCA2 security and was wondering: Are there efficient IND-CCA2 secure schemes that do not require plaintext awareness? I'm guessing yes - could someone point me to these schemes?

I was looking at Cramer-Shoup, and it seems like the general idea is that we make the message complex so that it's hard to come up with a valid ciphertext without using the encrypt algorithm, and then include a validity check in the decryption algorithm. However, this seems... not so nice, as this more or less makes the decryption oracle superfluous, since for a valid message the adversary would know the underlying plaintext anyway. I read (on wikipedia) that plaintext awareness is a very strong requirement and Semantic Security + Plaintext Awareness $\Rightarrow$ IND-CCA2. So ,I would like to read up on a system that does not make use of this approach.

• – user991 Aug 20 '14 at 11:48