Cryptanalysis of Liawʹs broadcasting Cryptosystem

In 1999, Liaw proposed a new broadcasting cryptosystem, which requires smaller bandwidth as compared to the previously proposed broadcasting cryptosystems. However, this article will show that the proposed system is insecure enough by presenting a conspiracy attack on it. We will also point out some ambiguous problems in Liawʹs paper. Moreover, we propose an improved broadcasting cryptosystem, which is a slight modification of the proposed system to overcome the conspiracy attack.