Efficient Anonymous Identity-Based Broadcast Encryption without Random Oracles

Broadcast encryption provides a method of secure multi-receiver communications, where a broadcaster can encrypt a message for a set S of users who are listening to a broadcast channel. Most identity-based broadcast encryption (IBBE) schemes are not anonymous, which means the attacker can obtain the identities of all receivers from the ciphertext. In this paper, the authors propose an efficient anonymous IBBE scheme in bilinear groups of prime order, where any attacker cannot get the identities of the receivers from the ciphertext. The scheme has constant size ciphertext and achieves adaptive security based on the asymmetric decisional bilinear Diffie-Hellman Exponent (DBDHE) assumption without random oracles. The proposed scheme improves efficiency and security of anonymous IBBE schemes simultaneously.