An efficient revocable identity‐based encryption with ciphertext evolution in the cloud‐assisted system

Abstract

Identity‐based encryption (IBE) is a public key cryptosystem on purpose to remove the traditional certificate management. How to realize efficient user revocation in the IBE is of great importance when considering its application. The drawback of most existing works is that the revoked user can still access the ciphertext prior to revocation. One possible solution proposed by Sun et al. is to evolve the ciphertext in the cloud. However, it is unfortunate that the master time key in their scheme is kept by the private key generator (PKG), which means it is sustained extra burden. In this article, we present an efficient revocable IBE with ciphertext evolution in the cloud‐assisted system and the ciphertext remains constant size. The cloud server keeps only one secret master time update key sent by the PKG in a private channel, and thus our scheme offers scalability. In the meantime, our detailed analysis demonstrates that our proposed scheme is semantically secure against ciphertext chosen attacks based on the k‐CAA problem and enjoys better efficiency in computation and communication costs compared with previous works.