A method is provided for determining a unique identifier of a device, the device including a quantum tunnelling barrier unique to the device. The method comprises applying a potential difference across the quantum tunnelling barrier, the potential difference sufficient to enable tunnelling of charge carriers through the quantum tunnelling barrier. The method further comprises measuring an electrical signal, the electrical signal representative of a tunnelling current through the quantum tunnelling barrier, the tunnelling current characteristic of the quantum tunnelling barrier. The method further comprises determining, from the measured electrical signal, a unique identifier for the device. Related apparatuses, systems, computer-readable media and methods are also provided herein.