International Association
for Cryptologic Research

To allow a delegator not only to delegate the keyword-controlled decryption rights of a broadcast encryption to a set of specified recipients, but also to control when the decryption rights will be delegated, in this paper, for the first time, we introduce a new notion called timed-release conditional proxy broadcast re-encryption (TR-CPBRE). We also propose a concrete construction for TR-CPBRE which can be proven selective identity adaptive CCA secure under the (P,Q,f)-GDDHE assumption, and chosen-time period chosen-ciphertext secure under the BDH assumption. When compared with the existing CPBRE and TR-PRE schemes, our scheme achieves better efficiency, and enables the delegator to make a fine-grained delegation of decryption rights to multiple delegatees.