Threshold Certificate-Based Encryption: Definition and Concrete Construction

Certificate-based encryption (CBE) is a new paradigm which overcomes the shortcomings of traditional public-key encryption and identity based encryption. CBE provides an efficient implicit certificate mechanism to eliminate third-party queries for the certificate status and to simplify 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 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 also inherits the properties of threshold encryption. We first formalize the definition and security model for TCBE. Then we construct a concrete TCBE scheme which is CCA-secure in the standard model.