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In broadcast encryption schemes, a distribution center broadcasts an encrypted message to a subset chosen from a universe of receivers and only the intended users are able to decrypt the message. Most broadcast encryption schemes do not provide anonymity and the identities of target receivers are sent in plaintext. However, in several applications, the authorized users' identities have the same sensitivity as the broadcasted messages. Yu, Ren and Lou (YRL) considered this issue and introduced an e icient anonymous a ribute-based broadcast encryption scheme. In this paper, we first propose an a ack on the YRL scheme and show that the unauthorized receivers can also decrypt the broadcasted message.Next, we propose the Improved-YRL scheme and prove that it achieves anonymity and semantic security under adaptive corruptions in the chosen ciphertext se ing. The proof is provided using the dual system encryption technique and is based on three complexity assumptions in composite order bilinear maps. The Improved-YRL scheme is a step forward in solving the long-standing problem of secure and low overhead anonymous broadcast encryption. Index TermsBroadcast Encryption, Ciphertext-Policy A ribute-Based Encryption (CP-ABE), Access Structure, Anonymity, Provable Security, A ack. ! IBroadcast Encryption. e concept of Broadcast Encryption (BE) [1] is used when a sender wants to send a message to an arbitrary subset chosen from a universe of receivers via an insecure broadcast channel. In this scenario, the distribution center chooses an arbitrary subgroup of receivers, S, encrypts the message due to the set S and broadcasts the ciphertext through the channel. In a secure broadcast encryption scheme, only the legitimate receivers which belong to the set S can decrypt the received message; while the unauthorized users obtain no information about the message even if they collude. e broadcast encryption schemes are helpful in several applications including TV subscription and electronic learning services [2] in which only the subscribed users who have paid to a certain channel• R. Rabaninejad is with the with the

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