Lightweight Dispatcher Constructions for Control Flow Flattening

Abstract

The objective of control flow obfuscation is to protect the program control flow from analysis. A technique called control flow flattening addresses static analysis by hiding edges between basic blocks in a program and introduces a dispatcher block that determines the execution order of the randomized blocks. In this paper we propose a novel flattening construction and lightweight dispatchers that do not impose high runtime performance impact on the program but still give good protection of the control flow against static analysis. We also present an attack model that allows us to quantitatively evaluate the protection the constructions give and compare against other suggestions from the literature. We have implemented our construction in the open source obfuscator OLLVM and present experimental results on overheads from different dispatcher implementations.