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.