SAT-Attack Resistant Hardware Obfuscation using Camouflaged Two-Dimensional Heterostructure Devices

Reverse engineering (RE) is one of the major security threats to the semiconductor industry due to the involvement of untrustworthy parties in an increasingly globalized chip manufacturing supply chain [1-5]. RE efforts have already been successful in extracting device level functionalities from an integrated circuit (IC) with very limited resources [6]. Camouflaging is an obfuscation method that can thwart such RE [7-9]. Existing work on IC camouflaging primarily uses fabrication techniques such as doping and dummy contacts to hide the circuit structure or build cells that look alike but have different functionalities. While promising these Si complementary metal oxide semiconductor (CMOS) based obfuscation techniques adds significant area overhead and are successfully decamouflaged by the Satisfiability solver (SAT)-based reverse engineering techniques [9-13]. Emerging solutions, such as polymorphic gates based on giant spin Hall effect (GSHE) are promising but adds delay overhead in hybrid CMOS-GSHE designs restricting the camouflaging to a maximum of 15% of all the gates in the circuit. Here, we harness the unique properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) including MoS2, MoSe2, MoTe2, WS2, and WSe2 and their optically transparent transition metal oxides (TMOs) to demonstrate novel area efficient camouflaging solutions that are resilient to SAT-attack and automatic test pattern generation (ATPG) attacks. We show that resistors with resistance values differing by 8 orders of magnitude, diodes with variable turn-on voltages and reverse saturation currents, and field effect transistors (FETs) with adjustable conduction type, threshold voltages and switching characteristics can be optically camouflaged to look exactly similar by engineering TMO/TMD heterostructures allowing hardware obfuscation of both digital and analog circuits. Since this 2D heterostructure devices family is intrinsically camouflaged, NAND/NOR/AND/OR gates in the circuit can be obfuscated with significantly less area overhead allowing 100% logic obfuscation compared to only 5% for CMOS-based camouflaging. Finally, we demonstrate that the largest benchmarking circuit from ISCAS’85, comprised of more than 4000 logic gates when obfuscated with the CMOS-based technique are successfully decamouflaged by SAT-attack in less than 40 minutes; whereas, it renders to be invulnerable even in more than 10 hours, when camouflaged with 2D heterostructure devices thereby corroborating our hypothesis of high resilience against RE. Our approach of connecting unique material properties to innovative devices to secure circuits can be considered as one of its kind demonstrations, highlighting the benefits of cross-layer optimization.