Dynamic Broadcast Encryption Scheme with Revoking User

Currently, there still lacks an efficient methodology to revoke user＇s ability to decrypt ciphertext in broadcast encryption with the uncertain number of ciphertext recipients. To solve this problem, here, we present a dynamic broadcast encryption scheme with the following properties： First, the length of the ciphertext has a linear relationship with the number of revocable users, but it has no association with the total number of ciphertext recipients. Sec- ond, the scheme also works when users dynamically join. Espe- cially, compared with methods published up to date, our scheme is more efficient with a large number of ciphertext recipients. Third, the broadcaster can revoke user＇s ability to decrypt ciphertext if necessary. Fourth, the private key of users is composed of three elements in Elliptic curve group of prime order. Last, if q-Deci- sional Multi-Exponent Bilinear Diffie-Hellman assumption holds, our scheme is secure in the standard model when a polynomial time adversary selectively attacks it.