Side Channel Analysis in Homomorphic Encryption

TL;DR

This paper reviews vulnerabilities of homomorphic encryption, especially fully homomorphic encryption, to side channel attacks, categorizes these weaknesses, presents case studies, and discusses mitigation strategies.

Contribution

It provides a comprehensive categorization of side channel vulnerabilities in FHE implementations and offers case studies and mitigation approaches.

Findings

FHE implementations are susceptible to side channel attacks.

Categorization of side channel analysis methods is proposed.

Mitigation strategies can reduce leakage risks.

Abstract

Homomorphic encryption provides many opportunities for privacy-aware processing, including with methods related to machine learning. Many of our existing cryptographic methods have been shown in the past to be susceptible to side channel attacks. With these, the implementation of the cryptographic methods can reveal information about the private keys used, the result, or even the original plaintext. An example of this includes the processing of the RSA exponent using the Montgomery method, and where 0's and 1's differ in their processing time for modular exponentiation. With FHE, we typically use lattice methods, and which can have particular problems in their implementation in relation to side channel leakage. This paper aims to outline a range of weaknesses within FHE implementations as related to side channel analysis. It outlines a categorization for side-channel analysis, some case studies, and mitigation strategies.