KeyMemRT Compiler and Runtime: Unlocking Memory-Scalable FHE

2026-01-26

AI Summary

This work addresses the high memory overhead of rotation keys in fully homomorphic encryption (FHE), which severely limits throughput in complex applications. The authors propose an MLIR-based compiler and runtime framework that, for the first time, enables automatic and fine-grained lifecycle management of both rotation and bootstrapping keys within an FHE compiler. By leveraging precise dataflow analysis to control key usage, the framework significantly reduces memory consumption while supporting arbitrary rotation indices. Designed as a modular backend, it integrates seamlessly with frontends such as Orion and HEIR, offering a general-purpose optimization layer for any FHE compiler. Experimental results demonstrate up to 1.74× and 1.16× reductions in memory usage compared to ANT-ACE and Fhelipe, respectively, along with performance improvements of 1.20× and 1.73×.

Technology Category

• Machine Learning: Hardware-aware ML
• Constraint Satisfaction and Optimization: Satisfiability Modulo Theories
• Search and Optimization: Heuristic Search

Application Category

• Security and Privacy: Applications of cryptography
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications
• Responsible Web: Measurement, analysis, and circumvention of Web censorship

Abstract

Fully Homomorphic Encryption (FHE) enables privacy preserving computation but it suffers from high latency and memory consumption. The computations are secured with special keys called rotation keys which often take up the majority of memory. In complex FHE applications, these rotation keys can cause a large memory bottleneck limiting program throughput. Existing compilers make little effort to solve this problem, instead relying on systems with massive memory availability. This resource requirement is a barrier to FHE uptake because optimizing FHE programs by hand is challenging due to their scale, complexity and expertise required. In this work, we present KeyMemRT; an MLIR based compiler and runtime framework that individually manages rotation key lifetimes to lower memory utilization and to allow arbitrary number of rotation indices to be supported without memory bloating. KeyMemRT relies on dataflow analysis to determine key lifetimes and is the first FHE compiler to provide automatic key management, handle fine-grained key-mangement and manage boostrap keys. We implement frontends for Orion and HEIR and show improvements over state-of-the-art FHE compilers. KeyMemRT achieves memory reduction of 1.74x and a speedup of 1.20x over ANT-ACE, and memory reduction of 1.16x and a speedup of 1.73x over memory-optimized compiler Fhelipe. We provide KeyMemRT as a post-optimizing compiler that can be targeted by any FHE compiler.

Problem

• Fully Homomorphic Encryption
• rotation keys
• memory bottleneck
• compiler optimization
• key management

Innovation

• KeyMemRT
• Fully Homomorphic Encryption
• rotation key management
• memory optimization
• MLIR-based compiler