# A Reconfigurable SRAM CRP PUF with High Reliability and Randomness
## 1 Introduction  
The rapid development of the internet of things (IoT) has ushered in an era of unprecedented connectivity and innovation, with IoT devices permeating virtually every aspect of our lives, owing to their efficiency, convenience, and insight. However, this connectivity necessitates enhanced security to address potential vulnerabilities such as unauthorized access, data breaches, and cyberattacks [1]. Existing security measures face various drawbacks, including resource constraints on IoT devices, cryptographic complexity, and evolving adversarial tactics [2, 3]. Alternative security paradigms suitable for the IoT's unique attributes must be explored to address these challenges. Physically unclonable functions (PUFs) present considerable potential due to their uniqueness, lightweight nature, and minimal resource requirements [4]. PUFs leverage inherent variations in electronic devices during manufacturing, providing distinct and unpredictable outputs for each device. This makes them ideal for secure cryptographic key generation and robust authentication [5, 6]. By harnessing physical variations' inherent randomness and uniqueness, PUFs present a dependable and tamper-resistant solution, as they can safeguard sensitive information and ensure digital system integrity. Unlike conventional cryptographic methods that depend on key storage, PUFs do not require the storage of sensitive data, enhancing their resilience to attacks [7]. PUFs can be categorized into non-silicon and silicon-based types [8]. Non-silicon PUFs present various physical properties of materials, such as optical [9], polymer-based [10],magnetic [11], carbon-based [12], and photonic crystal [13], and so on. They exploit specific material properties to generate unique challenge-response pairs. Conversely, silicon-based PUFs depend on inherent variations from manufacturing processes and environmental factors in silicon semiconductor devices. Silicon PUFs present various advantages, particularly their seamless integration into existing semiconductor technology, making them ideal for resource-constrained IoT environments. Silicon-based PUFs can be classified into two main categories based on their strength level corresponding to the number of Challenge-Response Pairs (CRPs): strong PUFs and weak PUFs. Weak PUFs produce a limited number of CRPs. These PUFs are ideally used in chip identification and cryptographic key generation [14]. Conversely, strong PUFs generate an extensive array of CRPs [15]. The availability of multiple CRPs enables the use of different challenges in multiple sessions without exhausting the pool of unique responses. Strong PUFs present excellent device identification and authentication protocols, ensuring a higher level of security against sophisticated attacks [16]. Extensive research has been conducted to develop strong PUF owing to their exceptional advantages [17; 18; 19; 20; 21]. For instance, a bistable ring (BR) comprising an even number of inverters is transformed into a strong BR PUF [17]. Ref. [18] presents a novel method for enhancing the CRP set of conventional ring oscillator-based PUFs. The reconfigurability presented in [19] exponentially increases the number of CRPs, presenting a strong Arbiter PUF (APUF) based on a typical 1T-1R RRAM array architecture. Furthermore, Ref. [20] presents a strong PUF generated from an existing weak switched-capacitor (SC)-based PUF. Ref. [21] presented a strong PUF using diode-clamped inverters operating in the subthreshold region. However, the large area requirement and power consumption of these devices considerably limit their implementation in IoT devices. Ref. [22] presented a pioneering approach to a strong PUF design, featuring a reconfigurable SRAM-based architecture with multiple CRPs. This PUF presented high power efficiency and compact area, while maintaining good CRP density. These characteristics make it particularly suitable for the authentication of IoT devices.