Revocable Identity-based Signcryption Scheme Without Random Oracles

Revocation functionality is crucial for the practicality of the public key cryptosystems including signcryption. When a user’s private key is corrupted by hacking or the period of a contract expires, the cryptosystems must provide a revocation method to revoke the misbehaving/compromised user. However, little work has been published on key revocation in identity-based signcryption. We propose a revocable identity-based signcryption scheme. In the scheme, the master key is randomly divided into two parts: one is used to construct the initial key, the other is used to generate the updated key. Furthermore, they are used to periodically and re-randomly generate full private keys for non-revoked users. Thus, the proposed scheme can revoke users and resist key exposure. In the standard model, we prove the proposed scheme with IND-CCA2 security under the DBDH hardness assumption and EUF-CMA security under the CDH hardness assumption.