Server-Aided Revocable Attribute-Based Encryption Revised: Multi-User Setting and Fully Secure

Attribute-based encryption (ABE) is a promising cryptographic primitive achieving fine-grained access control on encrypted data. However, efficient user revocation is always essential to keep the system dynamic and protect data privacy. Cui et al. (ESORICS 2016) proposed the first server-aided revocable attribute-based encryption (SR-ABE) scheme, in which an untrusted server manages all the long-term transform keys and update keys generated by key generation center (KGC) in order to achieve efficient user revocation. So, there’s no need for any user to communicate with KGC to update his/her decryption key regularly. In addition, the most part of computational overhead of decryption is outsourced to the server and user keeps a small size of private key to decrypt the final ciphertext. Then, Qin et al.’s (CANS 2017) extended Cui et al.s’ work to be decryption key exposure resistant (DKER).