Cryptanalysis and improvement of Petersen-Michels signcryption scheme

Petersen and Michels showed that Zheng's signcryption schemes lose confiden tiality to gain nonrepudiation. They also proposed another signcryption sch eme modified from a signature scheme giving message recovery. The authors s how that the Petersen-Michels scheme still violates the unforgeability prop erty, and propose an improvement that overcomes the security leak inherent in the scheme. The improvement is as efficient as previous signcryption sch emes with respect to both the computational cost and the communication over head.