Parasol Compiler: Pushing the Boundaries of FHE Program Efficiency

Fully Homomorphic Encryption (FHE) is a key technology to enable privacy-preserving computation. While optimized fhe implementations already exist, the inner workings of FHE are technically complex. This makes it challenging, especially for non-experts, to develop highly-efficient fHE programs that can exploit the advanced hardware of today. Although several compilers have emerged to help in this process, due to design choices, they are limited in terms of application support and the efficiency levels they can achieve. In this work, we showcase how to make fhe accessible to non-expert developers while retaining the performance provided by an expert-level implementation. We introduce Parasol, a novel end-to-end compiler encompassing a virtual processor with a custom Instruction Set Architecture (ISA) and a low-level library that implements FHE operations. Our processor integrates with existing compiler toolchains, thereby providing mainstream language support. We extract parallelism at multiple levels via our processor design and its computing paradigm. Specifically, we champion a Circuit Bootstrapping (CBS)-based paradigm, enabling efficient FHE circuit composition with multiplexers. Furthermore, Parasol's underlying design highlights the benefits of expressing fhe computations at a higher level-producing highly compact program representations. Our experiments demonstrate the superiority of Parasol, in terms of runtime (up to 17x faster), program size (up to $22 \times$ smaller), and compile time (up to $32 \times$ shorter) compared to the current state-of-the-art. We expect the fHE computing paradigm underlying Parasol to attract future interest since it exposes added parallelism for fhe accelerators to exploit.