Broadcast encryption is an effective way to broadcast a message securely such that more than one privileged receiver can decrypt it. The well-known constructions of identity-based broadcast encryption only support bounded broadcast users that had to deploy the maximum user number in advance. This is somewhat inefficient and impractical if the broadcast user number is predetermined. In this paper, we propose an adaptively secure identity-based broadcast encryption in the standard model that supports arbitrary number of users in broadcast set, which eliminates the size of public parameters with a constant number of group elements and obtain short ciphertexts, secret keys, and public parameters. We use the techniques of semi-functional ciphertexts and semi-functional keys in orthogonal subgroups to implement the boundless broadcast set and adaptive security by means of dual-system encryption mechanism in a composite-order group, and we prove the scheme to be fully secure without the random oracles in the static assumptions. The proposed scheme captures the properties of confidentiality, adaptive security, constant key, and short ciphertext. We also evaluate the computational costs and communication overheads and give the deployment in secure set-top box broadcast systems. Copyright © 2012 John Wiley & Sons, Ltd.