On the security of a convertible authenticated encryption

In this paper, we give security analysis to the convertible authenticated encryption scheme of Hung-Yu Chien [H.-Y. Chien, Convertible authenticated encryption scheme without using conventional one-way function, Informatica 14 (4) (2003) 1-9, Institute of Mathematics and Inforamtica, ISSN 0868-4952], and show that H.Y. Chien scheme have forgeability and repudiation; at the same time, we give the corresponding attack. Finally, we propose an improved publicly verifiable authenticated encryption schemes based on the Hung-Yu Chien Scheme. As for efficiency, the computation cost and communication overhead of our improved schemes are as small as the original schemes and in comparison with the original scheme, our improved scheme is more secure.