Attacks against Two Identity-Based Signcryption Schemes

Signcryption is an important cryptography primitive that provides confidentiality and authenticity for the messages simultaneously, at lower costs than traditional sign-then-encrypt method. This paper presents the attacks against two identity-based signcryption schemes: the Zhang et al.'s assertion signcryption scheme in decentralized autonomous environments, which is not consistent in multi-PKG scenarios, and the Yu et al.'s identity-based signcryption scheme in the standard model, which cannot achieve indistinguishability against chosen plaintext attacks.