Abstract
Ring signcryption is a cryptographic primitivewhich combines the functions of a ring signature scheme andan encryption scheme. It can provide confidentiality, anonymityand authenticity simultaneously. In this paper, we show asecurity flaw in a previous certificateless ring signcryptionscheme (Wang et al.’s scheme) and propose an efficient parallelring 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 encryptionoperations in our scheme implies a gain in running efficiency.We also prove that the new scheme is not only indistinguishableagainst chosen-ciphertext attacks but also existentially unforgeableagainst chosen-message attacks.