Anonymous identity-based encryption scheme without random oracles

The anonymous identity-based encryption (IBE) schemes are currently only selective-ID secure without random oracles or provably secure under a complex assumption. An anonymous IBE scheme based on decisional bilinear Diffie-Hellman (BDH) assumption in a group of composite order was proposed, which is ANON-IND-ID-CPA secure without random oracles and only needs two bilinear pairing computations. This scheme is more secure and efficient than the existing ones.