Cryptanalysis of Efficient Identity Based Signature/Signcryption Schemes in the Standard Model

Efficient identity based signature/signcryption in the standard model with full security has been pursued for a long time. At ISDPE'07, Ren and Gu claimed to construct efficient identity based signature/signcryption schemes with full security in the standard model. They claimed their schemes have short public parameters, high efficiency and a tight reduction. But in this paper we give attacks to their schemes to show their schemes are not secure.