Some Bounds and a Construction for Secure Broadcast Encryption

Abstract

We first present two tight lower bounds on the size of the secret keys of each user in an unconditionally secure one-time use broadcast encryption scheme (OTBES). Then we show how to construct a computationally secure multiple-use broadcast encryption scheme (MBES) from a key predistribution scheme (KPS) by using the ElGamal cryptosystem. We prove that our MBES is secure against chosen (message, privileged subset of users) attacks if the ElGamal cryptosystem is secure and if the original KPS is simulatable. This is the first MBES whose security is proved formally.