Practical Revocable Keyword Search Over Mobile Cloud-Assisted Internet of Things

Searchable encryption (SE) can potentially be used to guarantee both data confidentiality and searchability over mobile cloud-assisted Internet of Things. However, existing SE solutions mainly focus on user revocation rather than keyword revocation. The keyword revocation may be required in certain situations. For example, patients do not allow their doctors to access records on some diseases such as syphilis. Hence, we propose a basic revocable keyword search (RKS) scheme over encrypted electronic medical records in the group setting, which supports keyword revocation (by using a revocation list) and authorized access permissions (via a group key exchange protocol). Then, we design an enhanced RKS (called RKS+) to significantly reduce the size of revoked keyword ciphertexts and the costs of token generation and ciphertext retrieval. Our schemes also support efficient user revocation by updating only one index component, and guarantee forward security. The formal security analysis proves that our schemes are secure against both chosen-keyword attacks and chosen-plaintext attacks, and findings from the empirical evaluations demonstrate that our schemes are efficient and practical.