Import them both into Audacity. Apply the “Invert” effect to one of the tracks. Select both tracks, then from the “Tracks menu > Mix and Render”.
If the tracks were identical, the result will be silence. To check that it is absolute silence, select the full (mix) track, and open the “Amplify” effect. If the Amplify effect says that the “New Peak Amplitude” is “-infinity”, then the mix track is totally silent and the two imported files have identical audio.