Ring signature is a group-oriented signature with privacy concerns: any verifier can be convinced that the message has been signed by one of the members in the group, but the actual signer remains unknown. Several ring signature schemes based on bilinear pairings have been proposed. However, computational complexity for pairing computations of these ring signature schemes grows linearly with the size of the ring. In this paper, we propose an efficient ring signature with constant pairing computations and give its exact security proofs in the random oracle model under the Computational co-Diffie–Hellman assumption. We then investigate the performance of our scheme by choosing the Optimal- Ate pairing on the BN curve defined over a prime field at a 128-bit security level.