By; Dr. Saswat Kumar Ram
Assistant Professor
Department of Electronics and Communication Engineering
SRM University – AP( Amaravati)
A Physical Unclonable Function (PUF) provides a physically defined “digital fingerprint” output (response) for a given input and condition (challenge), that serves as a unique identifier, most often for a semiconductor device. These are called as challenge response pairs (CRPs). Due to deep submicron manufacturing process variations, every transistor in an IC has slightly different physical properties. These variations lead to small but measurable differences in electronic properties, such as transistor threshold voltages, temperature and process parameters. Since these process variations are not fully controllable during manufacturing, these physical device properties cannot be copied or cloned. PUF can be implemented in ICs and SoCs.
By utilizing these inherent variations, PUFs are very valuable for use as a unique identifier for any given IC. They do this through circuitry within the IC that converts the tiny variations into a digital pattern of 0s and 1s, which is unique for that specific chip and is repeatable over time. This pattern is a “silicon fingerprint,” comparable to its human biometric counterpart.
PUF (Physically Unclonable Function) metrics are measures of a PUF’s quality and performance, including Uniqueness, Reliability, Randomness, Uniformity, and Bit Aliasing, which are crucial for their application in hardware security, authentication, and key generation. These metrics assess a PUF’s ability to produce unique, repeatable, and random outputs in response to input challenges, despite environmental variations, making it difficult to clone or tamper with.
Key PUF Metrics
- Uniqueness: Measures how different the responses of distinct PUF devices are for the same challenge. A high uniqueness value indicates that each PUF produces a unique output, like a fingerprint for a device.
- Reliability: Assesses how consistently a PUF generates the same output for the same challenge under varying environmental conditions, such as temperature and voltage fluctuations.
- Randomness: Evaluates the unpredictability of a PUF’s output, ensuring it follows statistical randomness properties.
- Uniformity: Measures how evenly distributed the PUF’s output bits are, often assessed by checking if the number of 0s and 1s is approximately equal.
- Bit Aliasing (Bias): Indicates the tendency of a PUF to produce either a disproportionately high number of 0s or 1s, which can reveal information about the PUF’s design and affect its randomness.
Physical Unclonable Functions (PUFs) can be designed using the inherent variability in voltage regulators and charge pumps commonly employed in DC-DC conversion within modern power management ICs. Although recent advancements in artificial intelligence (AI) pose potential threats to the security of PUFs, these vulnerabilities can be mitigated by increasing the number of Challenge-Response Pairs (CRPs) and implementing circuit-level modifications to enhance unpredictability and resistance to modelling attacks. In line with evolving security requirements, FPGA-based PUFs have gained popularity due to their flexibility and ability to meet high-performance security demands. Additionally, the concept of Secure by Design (SbD) is increasingly being adopted, which emphasises integrating security considerations from the early stages of the design process, rather than addressing vulnerabilities at later stages.
