Threshold Defined Camouflaged Gates in 65nm Technology for Reverse Engineering Protection

Due to the ever-increasing threat of Reverse Engineering (RE) of Intellectual Property (IP) for malicious gains, camouflaging of logic gates is becoming very important. In this paper, we present experimental demonstration of transistor threshold voltage-defined switch [2] based camouflaged logic gates that can hide six logic functionalities i.e. NAND, AND, NOR, OR, XOR and XNOR. The proposed gates can be used to design the IP, forcing an adversary to perform brute-force guess-and-verify of the underlying functionality-increasing the RE effort. We propose two flavors of camouflaging, one employing only a pass transistor (NMOS-switch) and the other utilizing a full pass transistor (CMOS-switch). The camouflaged gates are used to design Ring-Oscillators (RO) in ST 65nm technology, one for each functionality, on which we have performed temperature, voltage, and process-variation analysis. We observe that CMOS-switch based camouflaged gate offers a higher performance (similar to 1.5 - 8X better) than NMOS-switch based gate at an added area cost of only 5%. The proposed gates show functionality till 0.65V. We are also able to reclaim lost performance by dynamically changing the switch gate voltage and show that robust operation can be achieved at lower voltage and under temperature fluctuation.