Methods for preventing activation of hardware backdoors installed in a digital circuit, the digital circuit comprising one or more hardware units to be protected. A timer is repeatedly initiated for a period less than a validation epoch, and the hardware units are reset upon expiration of the timer to prevent activation of a time-based backdoor. Data being sent to the hardware unit is encrypted in an encryption element to render it unrecognizable to a single-shot cheat code hardware backdoor present in the hardware unit. The instructions being sent to the hardware unit are reordered randomly or pseudo-randomly, with determined sequential restraints, using an reordering element, to render an activation instruction sequence embedded in the instructions unrecognizable to a sequence cheat code hardware backdoor present in the hardware unit.