DynaMO: Protecting Mobile DL Models through Coupling Obfuscated DL Operators

TL;DR

DynaMO introduces a dynamic obfuscation method for mobile deep learning models that significantly enhances security against runtime analysis attacks with minimal performance overhead.

Contribution

The paper proposes DynaMO, a novel fully dynamic model obfuscation technique that couples operators to protect mobile DL models from dynamic reverse engineering attacks.

Findings

DynaMO dramatically improves model security over static methods.

The obfuscation incurs negligible overhead on device.

Dynamic analysis tools can be thwarted effectively.

Abstract

Deploying DL models on mobile Apps has become ever-more popular. However, existing studies show attackers can easily reverse-engineer mobile DL models in Apps to steal intellectual property or generate effective attacks. A recent approach, Model Obfuscation, has been proposed to defend against such reverse engineering by obfuscating DL model representations, such as weights and computational graphs, without affecting model performance. These existing model obfuscation methods use static methods to obfuscate the model representation, or they use half-dynamic methods but require users to restore the model information through additional input arguments. However, these static methods or half-dynamic methods cannot provide enough protection for on-device DL models. Attackers can use dynamic analysis to mine the sensitive information in the inference codes as the correct model information and intermediate results must be recovered at runtime for static and half-dynamic obfuscation methods. We assess the vulnerability of the existing obfuscation strategies using an instrumentation method and tool, DLModelExplorer, that dynamically extracts correct sensitive model information at runtime. Experiments show it achieves very high attack performance. To defend against such attacks based on dynamic instrumentation, we propose DynaMO, a Dynamic Model Obfuscation strategy similar to Homomorphic Encryption. The obfuscation and recovery process can be done through simple linear transformation for the weights of randomly coupled eligible operators, which is a fully dynamic obfuscation strategy. Experiments show that our proposed strategy can dramatically improve model security compared with the existing obfuscation strategies, with only negligible overheads for on-device models.