Adaptively secure identity-based broadcast encryption with a constant-sized ciphertext

In this work, we present an adaptively secure

identity-based broadcast encryption system featuring constant

sized ciphertext in the standard model. The size of the public

key and the private keys of our system are both linear in

the maximum number of receivers. Also, our system is fully

collusion-resistant and has stateless receivers. Compared with the

state-of-the-art, our scheme is well optimized for the broadcast

encryption. The computational complexity of decryption of our

scheme depends only on the number of receivers, not the

maximum number of receivers of the system. Technically, we

employ dual system encryption technique and our proposal

offers adaptive security under the general subgroup decisional

assumption. Our scheme demonstrates that the adaptive security

of the schemes utilizing a composite order group can be proven

under the general subgroup decisional assumption while many

existing systems working in a composite order group are secure

under multiple subgroup decision assumptions. We note that this

finding is of an independent interest, which may be useful in other

scenarios.