Cryptanalysis and Improvement of Selvi et al.'s Identity-Based Threshold Signcryption Scheme

Signcryption can realize the function of encryption and signature in a reasonable logic step, which can lower computational costs and communication overheads. In 2008, S. S. D. Selvi et al. proposed an identitybased threshold signcryption scheme. In this paper, we show that the threshold signcryption scheme of S. S. D. Selvi et al. is vulnerable if the attacker can replaces the group public key. Then we point out that the receiver uses the senders’ public key without any verification in the unsigncrypt stage cause this attack. Further, we propose a probably-secure improved scheme to correct the vulnerable and give the unforgeability and confidentiality of our improved scheme under the existing security assumption.