Improved self-certified group-oriented cryptosystem without a combiner

In 2001, Ghodosi and Saeednia proposed a self-certified group-oriented cryptosystem without a combiner to prevent the Susilo et al.’s attack. However, in this paper we will show that their scheme is still insecure and probably suffers from the conspired attack. To remedy the weakness, an enhanced version is proposed while providing the new functionality to confirm the source of the encrypted message.