Security Analysis of Hardware Trojans on Approximate Circuits

Approximate computing, for error-tolerant applications, provides trade-offs for computations to achieve improved speed and power performance. Approximate circuits, in particular approximate arithmetic circuits, directly affect the performance of a computing system. Hence, approximate circuit designs have been extensively studied. However, security issues of approximate circuits have been ignored. Moreover, hardware Trojans have been found in fabricated chips in manufacturing industry chains by untrusted foundries. Hardware Trojans could affect the functionality of approximate circuits under very rare circumstances with inconsiderable footprints. In this paper, hardware Trojan insertion methods based on signal transition probability are utilized to investigate and evaluate the security threats in approximate circuits. A approximate low-partor-adder (LOA) adder is utilized as an example and analyzed in the paper. The evaluation results show that with the increase of the number of approximation modules, the approximate LOA adder is more possible to be inserted hardware Trojans than the exact LOA adder.