Method for detecting hardware trojan based on passive optical watermark

The invention provides a method for detecting hardware trojan based on a passive optical watermark. The method comprises the following steps: firstly, inserting a spare cell into a circuit, changing the spare cell for adding underlying metal into the spare cell, so that the density of the underlying metal in the spare cell is higher than that of a general functional unit; secondly, performing simulation to obtain a reflection imaging picture, namely, the passive optical watermark, of the underlying metal of the circuit on near-infrared light; thirdly, after circuit completion and before packaging, shooting an actual circuit from bottom to top; finally, comparing an actual watermark obtained by shooting with the watermark obtained by simulation, and if the watermark position is changed, the watermark disappears or a new watermark appears, determining that the hardware trojan exists in the circuit. According to the method, no electric testing on the circuit is performed, and the influences of process noise and measurement noise in a conventional method can be overcome, the detection complexity can be remarkably lowered and the detection accuracy can be improved.