Teaching an Old Dog New Tricks: Verifiable FHE Using Commodity Hardware

2024-12-04

arXiv.org

AI Summary

Fully homomorphic encryption (FHE) verifiability relies on expensive cryptographic proofs, hindering practical deployment. Method: This paper proposes Argos—the first FHE verifiability scheme leveraging generic trusted platform modules (TPMs), eliminating reliance on costly zero-knowledge proofs. Its core insight is the formal proof that program and data integrity—without confidentiality—is sufficient for FHE verifiability security. Based on this, Argos introduces a fixed-overhead TPM attestation protocol and architecturally eliminates microarchitectural side-channel risks. Contribution/Results: Implemented atop CKKS and TFHE, Argos supports real-world applications including PIR and PSI, and remains secure beyond the semi-honest model. It incurs only 6%–8% computational overhead during FHE evaluation—significantly lower than state-of-the-art cryptographic proof-based approaches—while preserving correctness, soundness, and integrity guarantees.

Technology Category

• Machine Learning: Hardware-aware ML
• Computer Vision: Adversarial Attacks & Robustness
• Knowledge Representation and Reasoning: Argumentation

Application Category

• Security and Privacy: Applications of cryptography
• Responsible Web: Data and user privacy-enhancing technologies for the Web
• User Modeling, Personalization and Recommendation: Attacks and countermeasures in recommendation systems

Abstract

We present Argos, a simple approach for adding verifiability to fully homomorphic encryption (FHE) schemes using trusted hardware. Traditional approaches to verifiable FHE require expensive cryptographic proofs, which incur an overhead of up to seven orders of magnitude on top of FHE, making them impractical. With Argos, we show that trusted hardware can be securely used to provide verifiability for FHE computations, with minimal overhead relative to the baseline FHE computation. An important contribution of Argos is showing that the major security pitfall associated with trusted hardware, microarchitectural side channels, can be completely mitigated by excluding any secrets from the CPU and the memory hierarchy. This is made possible by focusing on building a platform that only enforces program and data integrity and not confidentiality (which is sufficient for verifiable FHE, since all data remain encrypted at all times). All secrets related to the attestation mechanism are kept in a separate coprocessor (e.g., a TPM) inaccessible to any software-based attacker. Relying on a discrete TPM typically incurs significant performance overhead, which is why (insecure) software-based TPMs are used in practice. As a second contribution, we show that for FHE applications, the attestation protocol can be adapted to only incur a fixed cost. Argos requires no dedicated hardware extensions and is supported on commodity processors from 2008 onward. Our prototype implementation introduces 6% overhead to the FHE evaluation, and 8% for more complex protocols. In particular, we show that Argos can be adapted for real-world applications of FHE, such as PIR and PSI. By demonstrating how to combine cryptography with trusted hardware, Argos paves the way for widespread deployment of FHE-based protocols beyond the semi-honest setting, without the overhead of cryptographic proofs.

Problem

• Adding verifiability to FHE using trusted hardware
• Mitigating side channels by excluding CPU/memory secrets
• Enabling practical FHE applications like PIR and PSI

Innovation

• Uses trusted hardware for verifiable FHE
• Mitigates side channels by excluding CPU secrets
• Adapts attestation protocol for fixed cost