Abstract: Signcryption combines the functionalities of signature and encryption and costs less than the traditional approach.Online/Offline techniques can improve the efficiency of the signature and encryption,and one motivating application for this technology is mobile network devices.The previous attribute-based signcryption scheme is not practical and efficient,on the basis of Li’s attribute-based signature,an efficient attribute-based online/offline signcryption scheme was proposed in this paper.This scheme is provable secure in the random oracle model and it satisfies indistinguishability against adaptive chosen ciphertext attack based on l-th decisional bilinear Diffie-Hellman inversion (l-DBDHI) assumption and satisfies existential unforgeability against adaptive chosen message attack based on the standard computational Diffie-Hellman(CDH) assumption.Although the size of ciphertext increases,the new scheme achieves confindentiality and authentication,which is more suitable for the practical applications.

Key words: Signcryption,Online/Offline techniques,Attribute-based cryptography,Provable security