Polymorphic Sensor to Detect Laser Logic State Imaging Attack

Laser Logic State Imaging (LLSI) is a failure analysis (FA) technique which is conducted from the chip backside. LLSI provides an unlimited number of contactless probes to observe static signals, such as security critical assets, which in the hand of an attacker poses a significant threat. Countermeasures that have been proposed so far to prevent backside optical attacks have limitations, such as additional fabrication steps, large area overhead, incompatibility with digital circuits, which makes their implementation challenging. In this paper, we propose all-digital polymorphic gate sensors for the first time in hardware security to detect LLSI attacks. Polymorphic gates change their behavior depending on environmental conditions, e.g., variations in supply voltage and temperature. Freezing the system clock and modulation of supply voltage are the main requirements of mounting an LLSI attack. With these two attack requirements in mind, we design and simulate a polymorphic gate-based sensor that behaves as a NOR gate when there is no supply voltage modulation and switches behavior between NAND gate and NOR gate in the presence of modulation. The sensor is able to detect LLSI attacks 100% of the time at room temperature even considering manufacturing variation and with a detection rate of more than98% for a temperature range of 0°C to 85°C.