An efficient ID-based ring signcryption scheme

Signcryption is a cryptographic primitive that performs digital signature and public key encryption simultaneously, at lower computational costs and communication overheads than the signature-then-encryption approach. In 2005, Huang et al. proposed an identity-based ring signcryption scheme by combining the concepts of identity-based ring signature and signcryption together. However, their scheme is computationally inefficient, since the number of pairing computations grows linearly with the group size. In this paper, we propose an efficient identity-based ring signcryption scheme. Our scheme only needs four pairing computations for any group size. We then prove that the proposed scheme is secure against adaptive ciphertext attacks in the random oracle model assuming the Decisional Bilinear Diffie-Hellman problem is computationally hard.