Piezoresistive-Based Physical Unclonable Function

With the expansion of Internet-of-Things (IoT) devices in many aspects of our life, the security of such systems has become an important challenge. Unlike conventional computer systems, any IoT security solution should consider the constraints of these systems such as computational capability, memory, connectivity, and energy consumption limitations. Physical unclonable functions (PUFs) with their special characteristics were introduced as hardware-based solutions to satisfy the security needs while respecting the mentioned constraints. They exploit the uncontrollable and reproducible variations of the underlying components for security applications such as identification, authentication, and secure boot. Since IoT devices are typically low cost, it is important to reuse existing elements in their hardware (for instance, sensors, analog-to-digital converters (ADCs), etc.) instead of adding extra costs for the PUF hardware. Micro-electromechanical system (MEMS) devices are widely used in IoT systems as sensors and actuators. In this work, for the first time, a lightweight MEMS-based circuit with a piezoresistive bridge is introduced as a weak PUF. The piezoresistive PUF leverages the uncontrollable variations in the parameters of the circuit elements to derive secure keys for cryptographic applications. The experimental results show that our proposed piezoresistive PUF is capable of generating enough entropy for a complex key generation, while its responses show stability in different environmental conditions. The manufactured piezoresistive PUF shows a uniqueness of 47.73% and a reliability of 94.19%. Moreover, the generated secret keys passed the National Institute of Standards and Technology (NIST) test suite for randomness.