HE^2: A Communication-Light Heterogeneous Architecture for Efficient Fully Homomorphic Encryption

2026-05-29

AI Summary

This work addresses the significant computational and memory overheads of CKKS fully homomorphic encryption, which have limited existing ASIC or near-memory acceleration approaches due to high hardware costs, low efficiency, and severe heterogeneous communication latency. To overcome these challenges, the authors propose HE², a communication-light xPU-xMU heterogeneous acceleration architecture that, for the first time, systematically optimizes ModUp and ModDown operations at the dataflow graph (DFG) level. HE² integrates parallel keyswitch blocks to substantially reduce communication frequency and introduces a group-level pipelined execution mechanism that effectively exploits inter-group parallelism to hide communication latency. Compared to the state-of-the-art accelerator, HE² achieves a 1.66× end-to-end performance improvement, a 9.23× reduction in energy-delay-area product (EDAP), and limits communication stalls to only 6.67% of total execution latency.

Abstract

CKKS, an emerging fully homomorphic encryption (FHE) scheme, has been promising in privacy-preserving applications by enabling SIMD fixed-point computations on ciphertexts. Despite its strong security guarantees, CKKS involves both compute-intensive operators (ComOps) with high computational cost and memory-intensive operators (MemOps) with large memory footprints, making existing ASIC-based or NMP-based acceleration approaches suffer from high hardware overhead and limited efficiency. This observation motivates the integration of the architectural advantages of both paradigms into a heterogeneous xPU (ASIC)-xMU (NMP) architecture. However, in such a design, frequent and long-latency heterogeneous communication caused by the dominant keyswitch operator remains a key performance bottleneck. In this paper, we propose $HE^2$, a communication-light xPU-xMU heterogeneous FHE accelerator with dataflow graph (DFG) optimization and architecture co-design. First, we observe that the majority of communication arises at the interface between ModUp/ModDown and neighboring MemOps. To address this, we propose a DFG-level optimization framework to fully exploit the ModUp/ModDown reduction potential of the hoisting algorithm by identifying parallel keyswitch blocks and fusing them for reduced communication frequency. Second, we design an efficient heterogeneous architecture that adopts a group-level pipelined execution to effectively hide communication latency by leveraging the inherent parallelism across decomposed groups. End-to-end evaluation results show that $HE^2$ achieves 1.66$\times$ speedup and 9.23$\times$ lower EDAP (Energy-Delay-Area Product) compared to the state-of-the-art accelerator, with communication stalls accounting for only 6.67% of the total latency.

Problem

• Fully Homomorphic Encryption
• Heterogeneous Architecture
• Keystitch Communication
• CKKS
• Communication Bottleneck

Innovation

• heterogeneous architecture
• fully homomorphic encryption
• communication optimization
• dataflow graph
• keyswitch fusion