Abstract
To allow a delegator not only to delegate the keywordcontrolled 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 (TRCPBRE). We also propose a concrete construction for TR-CPBRE which can be proven selective identity adaptive CCA secure under the (P,Q, f)- general decisional Diffie-Hellman exponent assumption, and chosen-time period chosen-ciphertext secure under the bilinear Diffie-Hellman assumption. When compared with the existing CPBRE and Timed-Release Proxy Re-Encryption (TR-PRE) schemes, our scheme achieves better efficiency, and enables the delegator to make a fine-grained delegation of decryption rights to multiple delegatees.