DARTPHROG: A Superscalar Homomorphic Accelerator

Fully Homomorphic Encryption (FHE) allows a client to share their data with an external server without ever exposing their data. FHE serves as a potential solution for data breaches and the marketing of users' private data. Unfortunately, FHE is much slower than conventional asymmetric cryptography, where data are encrypted only between endpoints. Within this work, we propose the Dynamic AcceleRaTor for Parallel Homomorphic pROGrams, DARTPHROG, as a potential tool for accelerating FHE. DARTPHROG is a superscalar architecture, allowing multiple homomorphic operations to be executed in parallel. Furthermore, DARTPHROG is the first to utilize the new Hardware Optimized Modular-Reduction (HOM-R) system, showcasing the uniquely efficient method compared to Barrett and Montgomery reduction. Coming in at 40.5 W, DARTPHROG is one of the smaller architectures for FHE acceleration. Our architecture offers speedups of up to 1860 times for primitive FHE operations such as ciphertext/plaintext and ciphertext/ciphertext addition, subtraction, and multiplication when operations are performed in parallel using the superscalar feature in DARTPHROG. The DARTPHROG system implements an assembler, a unique instruction set based on THUMB, and a homomorphic processor implemented on a Field Programmable Gate Array (FPGA). DARTPHROG is also the first superscalar evaluation of homomorphic operations when the Number Theoretic Transform (NTT) is excluded from the design. Our processor can therefore be used as a base case for evaluation when weighing the resource and execution impact of NTT implementations.