Efficient Multi-client Order-Revealing Encryption and Its Applications

Order-revealing encryption (ORE) is a cryptographic primitive that enables ciphertext comparison while leaking nothing about the underlying plaintext beyond their lexicographic ordering. However, how to achieve efficient and secure ciphertext comparison for multi-user settings is still a challenging problem. In this work, we propose an efficient multi-client order-revealing encryption scheme (named m-ORE) by introducing a new token-based comparison method. Specifically, data owner is enabled to delegate token generation ability to some authorized users without revealing his secret key, and then each authorized user can perform comparison on ciphertexts from multiple data owners by generating the associated comparison tokens. Benefiting from our new method, m-ORE can not only reduce ciphertext size but also improve comparison efficiency, compared with the state-of-the-art (Cash et al. Asiacrypt 2018). Further, we present a non-interactive multi-client range query scheme by extending m-ORE. Finally, we show a formal security analysis and implement our scheme. The evaluation result demonstrates that m-ORE outperforms the scheme by Cash et al. in terms of both query and storage cost while achieving the same level of security.