A Provably Secure Parallel Certificatelesss Ring Signcryption Scheme

Ring signcryption is a cryptographic primitive which combines the functions of a ring signature scheme and an encryption scheme. It can provide confidentiality, anonymity and authenticity simultaneously. In this paper, we show a security flaw in a previous certificateless ring signcryption scheme (Wang et al.´s scheme) and propose an efficient parallel ring signcryption scheme in certificateless public key setting.Compared with Wang et al.´s scheme, our new scheme needs 3less pairings and enjoys a shorter ciphertext. Furthermore theparallel execution of the expensive signature and encryption operations in our scheme implies a gain in running efficiency.We also prove that the new scheme is not only indistinguishable against chosen-ciphertext attacks but also existentially unforgeable against chosen-message attacks.