Detection of probing attempts in secure ICs

Physical attacks focus on extracting information from internal parts of IC's. One way to achieve this is by means of connecting probes to wires, so that the content of internal buses and registers can be revealed. Protection against this type of attacks exists, but usually is bulky and expensive, e.g. the shielding of secured areas. This paper presents a novel in-circuit countermeasure that is cheap and can easily be integrated in existing designs to detect probing attempts. It is based on a ring oscillator that operates over coupled lines in a differential mode. When the loading of one of the lines is unbalanced over a tolerance margin, an impulse is generated and integrated over time. If the integration surpasses a given threshold an alarm signal is activated. Simulations show the stability of the detector over a range of temperature and supply voltage variations.