Cryptanalysis and improvement of a certificateless signcryption scheme without bilinear pairing

摘要

As an improtant cryptographic scheme, signcryption scheme has been widely used in applications since it could provide both of signature and encryption. With the development of the certificateless public key cryptography (CLPKC), many certincatelss signcryption (CLSC) schemes using bilinear pairing hve been proposed. Comparated other operations, the bilinear pairing operaion is much more com-pulicated. Therefore, CLSC scheme without bilinear pairing is more suitable for applications. Recently, Jing et al. proposed a CLSC scheme without bilinear pairing and claimed their scheme is secure against two types of adversaries. In this paper, we will show their scheme provide neither unforge-ability property nor confidentiality property. To improve security, we also propose a new CLSC scheme without pairing and demonstrate it is provably secure in the random oracle model.