Comments on 'Efficient Revocable Certificateless Encryption Secure in the Standard Model'
Yongkang Tang, Sherman S. M. Chow, Joseph K. Liu · The Computer Journal · 2013
Certificateless encryption (CLE) can be used to prevent the key generation centre from decrypting ciphertexts (which addresses the key escrow problem of identity-based encryption), but it cannot provide user revocation mechanism by default. A revocable CLE scheme was proposed by Shen et al. (2014. Efficient revocable certificateless encryption secure in the standard model. Comput. J., 57, 592–601) which realizes the revocation by requiring a time key in the decryption process. Despite of their security proofs, this paper shows an attack of their revocation mechanism.