The design goal of the proposed schemes is that the receiver can decrypt the ciphertext C normally at the decryption time specified by the sender. In this section, we introduce a common time server management organization to the system and further present our TRE system model based on Shamir secret sharing, as shown in Fig. 1. The system consists of five entities: the time server management organization, N time servers, the private key generator, the data sender, and the data receiver.