IND-CCA security ⇒ IND-CPA KEM

Fully-black-box reduction · standard model · folklore · security loss: tight: the reduction preserves the advantage exactly

Statement

Every IND-CCA-secure KEM is IND-CPA-secure: for every efficient IND-CPA adversary there is an efficient IND-CCA adversary with the same advantage — folklore.

Sketch

The IND-CPA game is the IND-CCA game without the decapsulation oracle, so an IND-CPA adversary is an IND-CCA adversary that makes no decapsulation queries.