Complete Robustness in Identity-Based Encryption

Complete robustness (CROB) was proposed to guarantee that for a public key encryption scheme, decryption attempts will fail with high probability if the wrong decryption key is used to decrypt a ciphertext, even if the keys are maliciously generated by the adversary. In this paper, we extend the notion of complete robustness to the identity-based setting. We firstly formalize the CROB for identity-based encryption, and present a generic construction achieving CROB from an arbitrary identity-based encryption scheme. After that, we investigate whether there exist some kind of relations between CROB and related-key attack (RKA) security for the case of identity-based encryption. We conclude that these two notions (CROB and RKA security) are separable for identity-based encryption, but with a slight modification to our generic construction, an identity-based encryption scheme offering complete robustness with security against related-key attacks can be constructed from any identity-based encryption scheme.