Practical Equi-Join Over Encrypted Database With Reduced Leakage

Secure join schemes, an important class of queries over encrypted databases, have attracted increasing attention. While efficient querying is paramount, data owners also emphasize the significance of privacy preservation. The state-of-the-art JXT (Jutla and Patranabis ASIACRYPT 2022) enables efficient join queries over encrypted tables with a symmetric-key solution. However, we observe that JXT inadvertently leaks undesirable query results as the number of queries increases. In this paper, we propose a novel equi-join scheme, One-Time Join Cross-Tags (OTJXT), which can avoid additional result leakage in multiple queries and extend to equi-join as opposed to natural join in JXT. Specifically, we design a new data encoding method using nonlinear transformations that reveals only the union of results for each query without extra leakage observed in JXT. Moreover, OTJXT addresses the linear search complexity issue (Shafieinejad et al. ICDE 2022) while preventing multiple query leakage. Finally, we implement OTJXT and compare its performance with JXT and Shafieinejad et al.'s scheme on the TPC-H dataset. The results show that OTJXT outperforms in search and storage efficiency, achieving a $\mathbf {98.5\times }$ (resp., $\mathbf {10^{6}\times }$) speedup in search latency and reducing storage cost by 62.5% (resp., 78.5%), compared to JXT (resp., Shafieinejad et al.'s scheme). Using OTJXT, a TPC-H query on a 40 MB database only takes 21 ms.