The signcryption is a relatively new cryptographic technique that is supposed to fulfill the functionalities of encryption and digital signature in a single logical step. Several signcryption schemes are proposed throughout the years, each of them having its own problems and limitations. In this paper, the security of a recent signcryption scheme, i.e. Hwang et al.'s scheme is analyzed, and it is proved that it involves several security flaws and shortcomings. Several devastating attacks are also introduced to the mentioned scheme whereby it fails all the desired and essential security attributes of a signcryption scheme.
Note: As originally published there is an error in the document's author byline. The name of the second author was listed as "Ali Asghar Beheshti Shirazi." The author wishes citations be credited to "Beheshti, A." The change is noted in Xplore's metadata but the PDF remains unchanged.