Aspects of the disclosed technology provide a method comprising executing, at a first processor and over a predetermined time period, first and second instructions in repeated alternations, wherein each alternation comprises executing the first instruction a predetermined number of times followed by executing the second instruction the predetermined number of times. Further, the method comprises measuring, via a measuring apparatus, a side-channel signal that results from the first processor executing the first and second instructions in repeated alternations. Additionally, the method comprises filtering, by a second processor, a spectral component of the measured side-channel signal, and analyzing, by the second processor, the filtered spectral component of the measured side-channel signal to determine power spectral density within a frequency range of the filtered spectral component.