Abstract
We propose a generic method that transforms a weakly secure KEM, i.e. a KEM which is secure against constrained chosen ciphertext attack (CCCA), to a strongly secure KEM, i.e. a KEM which is secure against full chosen ciphertext attack (CCA). The proposed method does not depend on the random oracle nor any other nonstandard assumptions. Using this method, we obtain new efficient hybrid encryption schemes based on Kurosawa&Desmedt and Hofheinz&Kiltz weakly secure KEMs. These are the first hybrid encryption schemes which are as efficient as Kurosawa&Desmedt and Hofheinz&Kiltz encryption schemes, but whose security can be explained in the original KEM/DEM framework.