A Generic Method for Reducing Ciphertext Length of Reproducible KEMs in the RO Model

Abstract

In this paper, a simple generic method is proposed which can make a key encapsulation mechanism (KEM) more efficient. While the original KEM needs to be OW-CCCA secure and to satisfy reproducibility, the transformed KEM is CCA secure in the random oracle model and the size of ciphertexts is shorter. In particular, various existing CCA secure KEMs in the standard model can be transformed into more efficient ones in the random oracle model. We can implement both the original KEM and the transformed one in a single chip simultaneously with a small number of additional gates because our transformation requires computing a single hash value only.