DNA: DC Nodal Analysis Attack for Evaluation of Analog Obfuscation Techniques

In recent years, various obfuscation techniques have been proposed to protect analog circuits against IP piracy attacks. To evaluate the strength of the analog obfuscation techniques, attack algorithms including the equation-based SMT attack, genetic algorithm, key spacing attack, and monotonic response algorithm have been proposed. However, unlike the digital domain, where the SAT attack is the de-facto standard for measuring the resiliency of the key-based locking techniques, no standard metric exists to evaluate analog obfuscation techniques. In this article, a novel DC nodal analysis (DNA) attack algorithm is proposed that requires only the circuit netlist and the large signal DC input-output response of an oracle IC. The DNA attack utilizes Kirchhoff’s voltage law (KVL) and Kirchhoff’s current law (KCL) to efficiently explore the obfuscated parameter space of an analog circuit and determine the correct control parameters that result in a circuit response similar to that of the oracle IC. The proposed attack is evaluated against four distinct analog circuits secured using key-based parameter obfuscation and multi-threshold obfuscation. The results from execution of the attack on a three stage front-end circuit secured with the key-based obfuscation technique indicate the successful elimination of 99.1% of keys from the search space in less than five days. The results from evaluating the attack on the same three stage front-end circuit secured with the multi-threshold obfuscation technique indicate the successful elimination of 99.98% of keys from the search space in 50.4 hours. With the limited information necessary to perform the attack, the efficiency in pruning the key-space when considering real world attack scenarios, and the ability to execute the attack across all current analog locking techniques, the DC nodal analysis attack provides a de-facto standard to measure the security provided by an analog obfuscation technique.