Trinity: A General Purpose FHE Accelerator

Fully Homomorphic Encryption (FHE) is crucial for privacy-preserving computing, which allows direct computation on encrypted data. While various FHE schemes have been proposed, none of them efficiently support both arithmetic FHE and logic FHE simultaneously. To address this issue, researchers explore the combination of different FHE schemes within a single application and propose algorithms for the conversion between them. Unfortunately, all prior ASIC-based FHE accelerators are designed to support a single FHE scheme, and none of them supports the acceleration for FHE scheme conversion. This necessitates FHE acceleration systems to integrate multiple accelerators for different schemes, leading to increased system complexity and hindering performance enhancement. In this paper, we present the first multi-modal FHE accelerator based on a unified architecture, which efficiently supports CKKS, TFHE, and their conversion scheme within a single accelerator. To achieve this goal, we first analyze the theoretical foundations of the aforementioned schemes and highlight their composition from a finite number of arithmetic kernels. Then, we investigate the challenges for efficiently supporting these kernels within a unified architecture, which include 1) concurrent support for NTT and FFT, 2) maintaining high hardware utilization across various polynomial lengths, and 3) ensuring consistent performance across diverse arithmetic kernels. To tackle these challenges, we propose a novel FHE accelerator named Trinity, which in-corporates algorithm optimizations, hardware component reuse, and dynamic workload scheduling to enhance the acceleration of CKKS, TFHE, and their conversion scheme. By adaptive select the proper allocation of components for NTT and MAC, Trinity maintains high utilization across NTTs with various polynomial lengths and imbalanced arithmetic workloads. The experiment results show that, for the pure CKKS and TFHE workloads, the performance of our Trinity outperforms the state-of-the- art accelerator for CKKS (SHARP) and TFHE (Morphling) by 1.49 x and 4.23 x, respectively. Moreover, Trinity achieves 919.3 x performance improvement for the FHE-conversion scheme over the CPU-based implementation. Notably, despite the performance improvement, the hardware overhead of Trinity is only 85 % of the summed circuit areas of SHARP and Morphling.