Threshold Certificate-based Encryption

Certificate-based encryption (CBE) is a new asymmetric encryption paradigm which combines traditional public-key encryption (PKE) and identity based encryption (IBE) while preserving some of their most attractive features. CBE provides an efficient implicit certificate mechanism to eliminate third-party queries for the certificate status and to simply the certificate revocation problem. Therefore, CBE can be used to construct an efficient PKI requiring fewer infrastructures. In addition, it also solves the key escrow problem and key distribution problem inherent in IBE. In this paper, we introduce a new notion called Threshold Certificate-Based Encryption (TCBE) to overcome the limitations of CBE due to the using of sole master key in the system. It preserves the advantages of CBE such as implicit certificate and no private key escrow. At the same time it inherits the properties of threshold encryption. We first formalize the definition and security model for TCBE. Then we propose a concrete TCBE scheme and prove it to be CCA-secure under the Decisional Bilinear Diffie-Hellman assumption in the standard model.