Multi-Client Order-Revealing Encryption

TL;DR

This paper introduces multi-client order-revealing encryption, enabling secure comparison of encrypted data from multiple clients, and provides new schemes with security proofs and performance improvements.

Contribution

It defines the concept and security model for multi-client order-revealing encryption and proposes two new schemes with security proofs in the random oracle model.

Findings

Two secure multi-client order-revealing encryption schemes are proposed.

Schemes are implemented with performance optimization methods.

Security is proven under the random oracle model.

Abstract

Order-revealing encryption is a useful cryptographic primitive that provides range queries on encrypted data since anyone can compare the order of plaintexts by running a public comparison algorithm. Most studies on order-revealing encryption focus only on comparing ciphertexts generated by a single client, and there is no study on comparing ciphertexts generated by multiple clients. In this paper, we propose the concept of multi-client order-revealing encryption that supports comparisons not only on ciphertexts generated by one client but also on ciphertexts generated by multiple clients. We also define a simulation-based security model for multi-client order-revealing encryption. The security model is defined with respect to the leakage function which quantifies how much information is leaked from the scheme. Next, we present two specific multi-client order-revealing encryption schemes with different leakage functions in bilinear maps and prove their security in the random oracle model. Finally, we give the implementation of the proposed schemes and suggest methods to improve the performance of ciphertext comparisons.