Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

FHE-SQL: Fully Homomorphic Encrypted SQL Database

Po-Yu Tseng, Po-Chu Hsu, Shih-Wei Liao

TL;DR

FHE-SQL addresses the privacy risks of outsourced databases by performing SQL query processing entirely over encrypted data using Fully Homomorphic Encryption, preventing data and query leakage to untrusted servers. It introduces a hybrid storage architecture that decouples metadata (RocksDB) from ciphertexts (blob storage), along with an oblivious query protocol and a formal UC-based security analysis for the PIR property. The paper details a practical FHE-based query pipeline featuring a Homomorphic Expression Tree and FHE-based PIR algorithms, and provides performance evaluations showing cryptographic overhead dominates while storage performance can be tuned via blob/RocksDB strategies. This work lays groundwork for private cloud databases with strong privacy guarantees, while highlighting the need for further advances in FHE efficiency and scalable query processing.

Abstract

FHE-SQL is a privacy-preserving database system that enables secure query processing on encrypted data using Fully Homomorphic Encryption (FHE), providing privacy guaranties where an untrusted server can execute encrypted queries without learning either the query contents or the underlying data. Unlike property-preserving encryption-based systems such as CryptDB, which rely on deterministic or order-preserving encryption and are vulnerable to frequency, order, and equality-pattern inference attacks, FHE-SQL performs computations entirely under encryption, eliminating these leakage channels. Compared to trusted-hardware approaches such as TrustedDB, which depend on a hardware security module and thus inherit its trust and side-channel limitations, our design achieves end-to-end cryptographic protection without requiring trusted execution environments. In contrast to high-performance FHE-based engines-Hermes, which target specialized workloads such as vector search, FHE-SQL supports general SQL query semantics with schema-aware, type-safe definitions suitable for relational data management. FHE-SQL mitigates the high cost of ciphertext space by using an indirection architecture that separates metadata in RocksDB from large ciphertexts in blob storage. It supports oblivious selection via homomorphic boolean masks, multi-tier caching, and garbage collection, with security proven under the Universal Composability framework.

FHE-SQL: Fully Homomorphic Encrypted SQL Database

TL;DR

FHE-SQL addresses the privacy risks of outsourced databases by performing SQL query processing entirely over encrypted data using Fully Homomorphic Encryption, preventing data and query leakage to untrusted servers. It introduces a hybrid storage architecture that decouples metadata (RocksDB) from ciphertexts (blob storage), along with an oblivious query protocol and a formal UC-based security analysis for the PIR property. The paper details a practical FHE-based query pipeline featuring a Homomorphic Expression Tree and FHE-based PIR algorithms, and provides performance evaluations showing cryptographic overhead dominates while storage performance can be tuned via blob/RocksDB strategies. This work lays groundwork for private cloud databases with strong privacy guarantees, while highlighting the need for further advances in FHE efficiency and scalable query processing.

Abstract

FHE-SQL is a privacy-preserving database system that enables secure query processing on encrypted data using Fully Homomorphic Encryption (FHE), providing privacy guaranties where an untrusted server can execute encrypted queries without learning either the query contents or the underlying data. Unlike property-preserving encryption-based systems such as CryptDB, which rely on deterministic or order-preserving encryption and are vulnerable to frequency, order, and equality-pattern inference attacks, FHE-SQL performs computations entirely under encryption, eliminating these leakage channels. Compared to trusted-hardware approaches such as TrustedDB, which depend on a hardware security module and thus inherit its trust and side-channel limitations, our design achieves end-to-end cryptographic protection without requiring trusted execution environments. In contrast to high-performance FHE-based engines-Hermes, which target specialized workloads such as vector search, FHE-SQL supports general SQL query semantics with schema-aware, type-safe definitions suitable for relational data management. FHE-SQL mitigates the high cost of ciphertext space by using an indirection architecture that separates metadata in RocksDB from large ciphertexts in blob storage. It supports oblivious selection via homomorphic boolean masks, multi-tier caching, and garbage collection, with security proven under the Universal Composability framework.
Paper Structure (24 sections, 1 theorem, 2 equations, 2 figures, 3 tables)

This paper contains 24 sections, 1 theorem, 2 equations, 2 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Preliminary
  3. Private Information Retrieval
  4. Fully Homomorphic Encryption
  5. FHE-Based PIR
  6. Related Works and Cryptanalytic Attacks
  7. Non-FHE Approaches
  8. FHE-Based Approaches
  9. Cryptanalytic Attacks
  10. FHE-SQL: System Design and Architecture
  11. System Architecture
  12. FHE-based PIR Algorithms
  13. Proof of Security for The PIR Property
  14. The Ideal Functionality: $\mathcal{F}_{FHE-SQL}$
  15. The Real World Protocol and Adversary
  16. ...and 9 more sections

Key Result

Theorem 1

The protocol $\Pi_{FHE-SQL}$ UC-realizes the ideal functionality $\mathcal{F}_{FHE-SQL}$ in the presence of a static, malicious adversary corrupting the server, assuming the underlying FHE and signature schemes are secure.

Figures (2)

  • Figure 1: Overview of FHE-SQL system architecture.
  • Figure 2: Diagram of a homomorphic key-value search, generating an encrypted selection mask.

Theorems & Definitions (2)

  • Theorem 1
  • proof : Proof Sketch