Paper 2010/277

Adaptively Secure Broadcast Encryption with Short Ciphertexts

Behzad Malek and Ali Miri

Abstract

We propose an adaptively secure broadcast encryption scheme with short ciphertexts. That is the size of the broadcast encryption message is fixed, regardless of the size of the broadcast group. In our proposed scheme, members can join and leave the group without requiring any change to public parameters of the system or private keys of existing members. Our construction has a twofold improvement over best previously known broadcast encryption schemes. First, we propose a scheme that immediately yields adaptive security in the CCA model without any (sub-linear) increase in the size of ciphertexts or use of a random oracle. Secondly, the security model in our system includes decryption queries for any member, even including the members in the challenge set. This a more secure model, as it is closer to the adversary in real world.