Paper 2025/1989

HardCODE: Hardware-based Circuit Obfuscation using Data Encryption

Abstract

Indistinguishability Obfuscation (iO) renders indistinguishable any pair of same-sized and functionally identical circuits. Since its introduction by Barak et al. (Crypto ’01), iO has become the holy grail of modern cryptography due to the myriad of applications it enables. Despite several theoretical constructions (including recent breakthrough results from well-studied assumptions), practically efficient frameworks for iO have remained out of reach. In this paper, we formally introduce the notion of Hardware-based indistinguishability obfuscation (HiO) with an aim to make iO practical. Further, we present a novel framework called Hardware-based Circuit Obfuscation from Data Encryption (HardCODE) for realizing highly efficient HiO. Given a simple tamper-proof hardware to store a fixed size secret key, our proposed HardCODE framework yields a provably secure hardware module that achieves iO for all poly-sized circuits, while additionally relying on any one-way function and certain (heuristic but widely studied) assumptions on substitution-permutation networks (used extensively in the design of secure block ciphers). We practically instantiate HardCODE from widely deployed realizations of a simple HSM (Hardware Security Module), and the substitution-permutation network underlying the PRESENT block cipher (an ISO standard for lightweight cryptography). We then use this instance of HardCODE to obfuscate, without loss of generality, the C-17 circuit of the ISCAS-85 benchmark suite, while incurring very small practical overheads. To the best of our knowledge, this constitutes the first practical demonstration of iO.