Cloud-Aided Scalable Revocable IBE with Ciphertext Update from Lattices in the Random Oracle Model

Cloud-aided scalable revocable identity-based encryption with ciphertext update (CA-RIBE-CU), first introduced by Wang et al. in 2017 and the first lattice-based instantiation constructed by Zhang et al. in 2021, offer significant advantages over previous identity revocation mechanisms when considering the scenario of secure data sharing in the cloud setting. In this primitive, the receiver can utilize the short-term decryption keys to decrypt all encrypted data sent to him or her, meanwhile, the ciphertexts stored in the cloud will update to new ones with the aided of an untrusted cloud service provider (CSP) and without any interaction with the data owners, and thus, the revoked receivers cannot access to both previously and subsequently shared data, that is, to achieve both identity revocation and ciphertext update simultaneously for IBE. In this paper, inspired by the first quantum resistant construction of CA-RIBE-CU by Zhang et al. in FCS 2021, we propose a new lattice-based CA-RIBE-CU scheme in the random oracle model (ROM). We also adopt the two interesting tools “hybrid ciphertexts” and “hybrid short-term decryption keys” proposed by Zhang et al. to enable constant ciphertexts and simplified ciphertexts update. Differently, instead of using a super-lattice to issue the long-term private keys and the time update keys, our new construction is based on the main technique for lattice basis delegation without dimension increase, which benefits the new CA-RIBE-CU scheme with much shorter items in almost all keys and final ciphertexts, thus enriching the research of lattice-based revocable IBE.