HOP: Hardware makes Obfuscation Practical

Abstract

Program obfuscation is a central primitive in cryptography, and has important real-world applications in protecting software from IP theft. However, well known results from the cryptographic literature have shown that software only virtual black box (VBB) obfuscation of general programs is impossible. In this paper we propose HOP, a system (with matching theoretic analysis) that achieves simulation-secure obfuscation for RAM programs, using secure hardware to circumvent previous impossibility results. To the best of our knowledge, HOP is the first implementation of a provably secure VBB obfuscation scheme in any model under any assumptions. HOP trusts only a hardware single-chip processor. We present a theoretical model for our complete hardware design and prove its security in the UC framework. Our goal is both provable security and practicality. To this end, our theoretic analysis accounts for all optimizations used in our practical design, including the use of a hardware Oblivious RAM (ORAM), hardware scratchpad memories, instruction scheduling techniques and context switching. We then detail a prototype hardware implementation of HOP. The complete design requires 72% of the area of a V7485t Field Programmable Gate Array (FPGA) chip. Evaluated on a variety of benchmarks, HOP achieves an overhead of 8× ∼ 76× relative to an insecure system. Compared to all prior (not implemented) work that strives to achieve obfuscation, HOP improves performance by more than three orders of magnitude. We view this as an important step towards deploying obfuscation technology in practice. Permission to freely reproduce all or part of this paper for noncommercial purposes is granted provided that copies bear this notice and the full citation on the first page. Reproduction for commercial purposes is strictly prohibited without the prior written consent of the Internet Society, the first-named author (for reproduction of an entire paper only), and the author's employer if the paper was prepared within the scope of employment.

Field experience with obfuscating million‐user iOS apps in large enterprise mobile development

“…Although software obfuscation has been actively researched for quite some time, how to systematically assess the security strength of an obfuscator remains an open problem. For cryptographic obfuscation, the evaluation methodology is clear, ie, reducing deobfuscation to a computational problem with provable or conjectural intractability . In contrast, evaluation through empirical experiments always raises concerns about the possibility that the obfuscation can be effectively nullified by some unknown or future deobfuscation methods not considered by the evaluation.…”

“…Ascend, GhostRider, Phantom, and Raccoon are implementations of secure processors or hardware‐software systems that achieves achieves memory obliviousness when executing obfuscated programs. HOP is another secure processor that provides oblivious memory access; moreover, it is resilient to rewinding attacks by making the processor stateless.…”

“…For cryptographic obfuscation, the evaluation methodology is clear, ie, reducing deobfuscation to a computational problem with provable or conjectural intractability. 48 In contrast, evaluation through empirical experiments always raises concerns about the possibility that the obfuscation can be effectively nullified by some unknown or future deobfuscation methods not considered by the evaluation. Some recent effort has tried to establish standards for assessing the security strength of obfuscation techniques, [49][50][51] but it remains unclear how well they can fit the demands of practical software protection.…”

Implementing Conjunction Obfuscation Under Entropic Ring LWE

“…Although we take a software-only-based approach to program obfuscation, hardware-based approaches are also feasible. The work [49] achieves simulation-secure obfuscation for RAM programs using secure hardware to circumvent previous impossibility results.…”

Deterministic, Stash-Free Write-Only ORAM

“…ORAM solutions that have been proposed provide strong privacy by guaranteeing that anyone who observes the entire communication channel between client and backend storage cannot distinguish any series of accesses from random. Due to this strong privacy guarantee, ORAM has been used as a powerful tool in various application settings such as secure cloud storage (e.g., [16,27,28]), secure multi-party computation (e.g., [10,14,15,32,34]), and secure processors (e.g., [8,13,19]). This paper is authored by an employee(s) of the United States Government and is in the public domain.…”