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On the Feasibility of Hybrid Homomorphic Encryption for Intelligent Transportation Systems

Kyle Yates, Abdullah Al Mamun, Mashrur Chowdhury

TL;DR

This work assesses the feasibility of Hybrid Homomorphic Encryption (HHE) for Intelligent Transportation Systems (ITS) by combining a homomorphic scheme with a symmetric cipher to dramatically reduce ciphertext sizes and communication overhead. It centers on the Rubato HHE scheme and develops ITS-relevant theoretical models and parameter-based analyses to estimate ciphertext sizes and payload capacities under realistic V2X/I2I workloads. The findings indicate that Rubato can achieve order-of-magnitude reductions in ciphertext expansion compared with pure HE, enabling latency-constrained ITS communication while preserving cryptographic security. The study identifies practical advantages for RSU–Cloud backhaul flows and outlines future experimental validation necessary to confirm these theoretical gains in real-world ITS deployments.

Abstract

Many Intelligent Transportation Systems (ITS) applications require strong privacy guarantees for both users and their data. Homomorphic encryption (HE) enables computation directly on encrypted messages and thus offers a compelling approach to privacy-preserving data processing in ITS. However, practical HE schemes incur substantial ciphertext expansion and communication overhead, which limits their suitability for time-critical transportation systems. Hybrid homomorphic encryption (HHE) addresses this challenge by combining a homomorphic encryption scheme with a symmetric cipher, enabling efficient encrypted computation while dramatically reducing communication cost. In this paper, we develop theoretical models of representative ITS applications that integrate HHE to protect sensitive vehicular data. We then perform a parameter-based evaluation of the HHE scheme Rubato to estimate ciphertext sizes and communication overhead under realistic ITS workloads. Our results show that HHE achieves orders-of-magnitude reductions in ciphertext size compared with conventional HE while maintaining cryptographic security, making it significantly more practical for latency-constrained ITS communication.

On the Feasibility of Hybrid Homomorphic Encryption for Intelligent Transportation Systems

TL;DR

This work assesses the feasibility of Hybrid Homomorphic Encryption (HHE) for Intelligent Transportation Systems (ITS) by combining a homomorphic scheme with a symmetric cipher to dramatically reduce ciphertext sizes and communication overhead. It centers on the Rubato HHE scheme and develops ITS-relevant theoretical models and parameter-based analyses to estimate ciphertext sizes and payload capacities under realistic V2X/I2I workloads. The findings indicate that Rubato can achieve order-of-magnitude reductions in ciphertext expansion compared with pure HE, enabling latency-constrained ITS communication while preserving cryptographic security. The study identifies practical advantages for RSU–Cloud backhaul flows and outlines future experimental validation necessary to confirm these theoretical gains in real-world ITS deployments.

Abstract

Many Intelligent Transportation Systems (ITS) applications require strong privacy guarantees for both users and their data. Homomorphic encryption (HE) enables computation directly on encrypted messages and thus offers a compelling approach to privacy-preserving data processing in ITS. However, practical HE schemes incur substantial ciphertext expansion and communication overhead, which limits their suitability for time-critical transportation systems. Hybrid homomorphic encryption (HHE) addresses this challenge by combining a homomorphic encryption scheme with a symmetric cipher, enabling efficient encrypted computation while dramatically reducing communication cost. In this paper, we develop theoretical models of representative ITS applications that integrate HHE to protect sensitive vehicular data. We then perform a parameter-based evaluation of the HHE scheme Rubato to estimate ciphertext sizes and communication overhead under realistic ITS workloads. Our results show that HHE achieves orders-of-magnitude reductions in ciphertext size compared with conventional HE while maintaining cryptographic security, making it significantly more practical for latency-constrained ITS communication.
Paper Structure (10 sections, 1 equation, 3 figures, 3 tables)

This paper contains 10 sections, 1 equation, 3 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Our Contributions
  3. Notation and Preliminaries
  4. Notations
  5. Homomorphic Encryption
  6. Hybrid Homomorphic Encryption
  7. Rubato
  8. Applications of HHE in ITS
  9. Theoretical Evaluation of HHE for ITS
  10. Conclusion and Future Work

Figures (3)

  • Figure 1: Hybrid homomorphic encryption protocol.
  • Figure 1: Hybrid homomorphic encryption model.
  • Figure 2: Overview of the HHE-enabled I2I workflow. Each RSU first homomorphically encrypts its symmetric key (Step 1). During operation, aggregated BSMs are encrypted using lightweight symmetric cryptography and uploaded to the cloud (Step 2). The cloud reconstructs the homomorphic ciphertext (Step 3) and performs encrypted analytics without decryption (Step 4). The encrypted results are sent back to the TMC or RSU for decryption (Step 5).