Cryptanalysis and improvement of signcryption schemes

In 1997, two new schemes for authenticated encryption, called signcryption, were proposed by Zheng. In the paper, the authors point out a serious problem with these schemes. In fact, the way to gain nonrepudiation violates the confidentiality. The authors compare the schemes to previously known authenticated encryption schemes which were not mentioned by Zheng. Finally, the authors outline a solution that helps to overcome the problem.