Paper 2006/207

The Kurosawa-Desmedt Key Encapsulation is not Chosen-Ciphertext Secure

Javier Herranz and Dennis Hofheinz and Eike Kiltz

Abstract

At CRYPTO 2004, Kurosawa and Desmedt presented a hybrid public-key encryption scheme that is chosen-ciphertext secure in the standard model. Until now it was unknown if the key-encapsulation part of the Kurosawa-Desmedt scheme by itself is still chosen-ciphertext secure or not. In this short note we answer this question to the negative, namely we present a simple chosen-ciphertext attack on the Kurosawa-Desmedt key encapsulation mechanism.