Server-Aided Revocable Identity-Based Encryption from Lattices

Server-aided revocable identity-based encryption (SR-IBE), recently proposed by Qin et al. at ESORICS 2015, offers significant advantages over previous user revocation mechanisms in the scope of IBE. In this new system model, almost all the workloads on users are delegated to an untrusted server, and users can compute decryption keys at any time period without having to communicate with either the key generation center or the server. In this paper, inspired by Qin et al.’s work, we design the first SR-IBE scheme from lattice assumptions. Our scheme is more efficient than existing constructions of lattice-based revocable IBE. We prove that the scheme is selectively secure in the standard model, based on the hardness of the Learning with Errors problem. At the heart of our design is a “double encryption” mechanism that enables smooth interactions between the message sender and the server, as well as between the server and the recipient, while ensuring the confidentiality of messages.