Aspects of the disclosed technology provide a method comprising executing different first and second instructions a first and second number of times, respectively, in repeated alternations. The method further comprises measuring spectra of signals emanating as a result of the processor executing the first and second instructions. The method also includes analyzing data indicative of the spectra of the signals to determine side-channel candidate side-band pairs that each have a lower and upper sideband at first and second frequencies, respectively, that are separated by approximately twice the respective alternation frequency. Finally, the method includes identifying a side-channel carrier frequency at a frequency approximately at a midpoint between a side-channel candidate side-band pair's first and second frequency.