Cryptanalysis of an Identity Based Signcryption Scheme without Random Oracles

Signcryption is a cryptographic primitive that aims at providing confidentiality and the sender’s identity authentication in a logic step, at lower computational costs and communication overheads than sign-then-encrypt way. Recently, Yu et al.[1] proposed a new identity based signcryption scheme in standard model. However, in this paper, we show that the scheme still has some security weaknesses. Further, we propose a corrected version of the scheme and formally prove its security under the existing security model for identity-based signcryption.