Hardware Obfuscation of the 16-bit S-box in the MK-3 Cipher

J. Blocklove (Rochester Inst. of Techn., USA), S. Farris, M. Kurdziel (L3Harris Technologies, USA), M. Łukowiak, S. Radziszowski (Rochester Inst. of Techn., USA)

At different stages of the Integrated Circuit (IC) lifecycle there are attacks which threaten to compromise the integrity of the design through piracy, reverse engineering, hardware Trojan insertion, side channel analysis, and other physical attacks. Some of the most notable challenges in this field deal specifically with Intellectual Property (IP) theft and reverse engineering attacks. One method by which some of these concerns can be addressed is by introducing hardware obfuscation to the design in various forms. In this work we evaluate the effectiveness of a few different forms of netlist-level hardware obfuscation on a 16-bit substitution box component of a customizable cipher MK-3. These obfuscation methods were attacked using a satisfiability (SAT) attack, which is able to iteratively rule out classes of keys at once. This has been shown to be very effective against many forms of hardware obfuscation. A method to successfully defend against this attack is described in this paper. This method introduces a modified SIMON block cipher as a One-way Random Function (ORF) that is used to generate an obfuscation key. The substitution box obfuscated using this 32-bit key and a round-reduced implementation of the SIMON cipher is shown to successfully secure the substitution box against a SAT attack for at least 5 days.