Are ring oscillators without a combinatorial loop good enough for Hardware Trojan detection?

Hardware Trojan detection is a very serious issue for Integrated Circuit design and fabrication especially for those used in critical applications. The main target of this malicious hardware is to access and exploit the information stored and/or processed on an IC. Therefore, countermeasures must be designed for protection against HTs. In this direction many runtime and test-time monitoring approaches have been proposed. In run-time techniques, special monitoring sensors are used in order to detect local variations of the design characteristics, due to the presence of a HT. Most sensors are based on the classical ring oscillators that change their oscillation frequency when a HT is present. Recently two new types of oscillators without a combinatorial loop have been proposed, both different from the classical ring oscillators. In this paper a study and a statistical approach about the efficient use of the new oscillators as the main part of a HT detection technique, instead of the classical ring oscillator, are presented.