Hardware trojan state detection for analog circuits and systems

Abstract

The circuit structures with positive feedback loops are likely to have multiple operating points, and the unwanted Trojan state is easy to be triggered by process, voltage, and temperature variation or user's action. In this paper, circuit-level Homotopy methods are used to find all operating points and detect Trojan states. Furthermore, the temperature characteristic of the positive feedback loop circuits can also identify the Trojan state. Examples are given to show both Homotopy and temperature methods are valid.

Challenges and Opportunities in Analog and Mixed Signal (AMS) Integrated Circuit (IC) Security

“…Authors in [64,65,67] proposed unwanted yet stable DC operating points in few circuits (having more than one operating point) as Trojan states and these can be triggered both in static and dynamic circuits by changing initial conditions or manufacturing process or temperature variations. Once the Trojan is triggered, its functionality can change.…”

“…The circuit can even stop functioning, like a Wien bridge oscillator which stops oscillating when it encounters an unwanted state of operation [65]. Although these proposed Trojans have the characteristics of analog Trojans, they are only applicable for a few types of circuits like oscillators, filter [64], bias generators having positive feedback loops [65,66], and opamps using slew rate enhancement (SRE) circuits [67]. The triggering of such Trojans seems impossible with a start-up circuit already available in most analog/AMS chips which negates the possibility of any unwanted operating states.…”

Temperature signatures for performance assessment of circuits with undesired equilibrium states

“…This method is also useful for identifying some of the challenges associated with verifying the absence of undesired equilibrium points in the presence of PVT variations. Temperature sweeping: The temperature sweeping method is based on doing a homotopy-type simulation by conducting a bidirectional widerange temperature sweep [3,4] with a circuit simulator. Results similar to those depicted in Fig.…”

“…The temperature sweeping method is based on doing a homotopy‐type simulation by conducting a bidirectional wide‐range temperature sweep [3, 4] with a circuit simulator. Results similar to those depicted in Fig.…”

“…Homotopy methods can be used to verify the presence or absence of multiple equilibriums [2, 3] with standard simulators if the positive feedback loops are correctly identified; however, these simulations can be very time consuming and systematic methods have not evolved for identifying critical positive feedback loops. Since equilibrium states are invariably PVT dependent, verification that a circuit is void of undesired equilibrium states at one PVT point does not guarantee correct circuit operation at other PVT locations.…”