Hardware Security For and Beyond CMOS Technology: An Overview on Fundamentals, Applications, and Challenges <s> Physically-Unclonable Functions (PUFs) <s> Modern cryptographic practice rests on the use of one-way functions, which are easy to evaluate but difficult to invert. Unfortunately, commonly used one-way functions are either based on unproven conjectures or have known vulnerabilities. We show that instead of relying on number theory, the mesoscopic physics of coherent transport through a disordered medium can be used to allocate and authenticate unique identifiers by physically reducing the medium's microstructure to a fixed-length string of binary digits. These physical one-way functions are inexpensive to fabricate, prohibitively difficult to duplicate, admit no compact mathematical representation, and are intrinsically tamper-resistant. We provide an authentication protocol based on the enormous address space that is a principal characteristic of physical one-way functions. <s> BIB001 </s> Hardware Security For and Beyond CMOS Technology: An Overview on Fundamentals, Applications, and Challenges <s> Physically-Unclonable Functions (PUFs) <s> Physical unclonable functions (PUFs) can be used as a cost-effective means to store cryptographic key material in an unclonable way. They can be employed for strong authentication of objects, e.g., tokens, and of persons possessing such tokens, but also for other purposes. We give a short overview of security applications where PUFs are useful, and discuss physical realisations, noisy measurements and information content of PUFs. Then we describe an integrated authentication token containing an optical PUF, a challenging mechanism and a detector. Finally, we discuss authentication protocols for controlled and uncontrolled PUFs. <s> BIB002 </s> Hardware Security For and Beyond CMOS Technology: An Overview on Fundamentals, Applications, and Challenges <s> Physically-Unclonable Functions (PUFs) <s> The idea of using intrinsic random physical features to identify objects, systems, and people is not new. Fingerprint identification of humans dates at least back to the nineteenth century [21] and led to the field of biometrics. In the 1980s and 1990s of the twentieth century, random patterns in paper and optical tokens were used for unique identification of currency notes and strategic arms [2, 8, 53]. A formalization of this concept was introduced in the very beginning of the twenty-first century, first as physical one-way functions [41, 42], physical random functions [13], and finally as physical(ly) unclonable functions or PUFs.1 In the years following this introduction, an increasing number of new types of PUFs were proposed, with a tendency toward more integrated constructions. The practical relevance of PUFs for security applications was recognized from the start, with a special focus on the promising properties of physical unclonability and tamper evidence. <s> BIB003 </s> Hardware Security For and Beyond CMOS Technology: An Overview on Fundamentals, Applications, and Challenges <s> Physically-Unclonable Functions (PUFs) <s> We discuss numerical modeling attacks on several proposed strong physical unclonable functions (PUFs). Given a set of challenge-response pairs (CRPs) of a Strong PUF, the goal of our attacks is to construct a computer algorithm which behaves indistinguishably from the original PUF on almost all CRPs. If successful, this algorithm can subsequently impersonate the Strong PUF, and can be cloned and distributed arbitrarily. It breaks the security of any applications that rest on the Strong PUF's unpredictability and physical unclonability. Our method is less relevant for other PUF types such as Weak PUFs. The Strong PUFs that we could attack successfully include standard Arbiter PUFs of essentially arbitrary sizes, and XOR Arbiter PUFs, Lightweight Secure PUFs, and Feed-Forward Arbiter PUFs up to certain sizes and complexities. We also investigate the hardness of certain Ring Oscillator PUF architectures in typical Strong PUF applications. Our attacks are based upon various machine learning techniques, including a specially tailored variant of logistic regression and evolution strategies. Our results are mostly obtained on CRPs from numerical simulations that use established digital models of the respective PUFs. For a subset of the considered PUFs-namely standard Arbiter PUFs and XOR Arbiter PUFs-we also lead proofs of concept on silicon data from both FPGAs and ASICs. Over four million silicon CRPs are used in this process. The performance on silicon CRPs is very close to simulated CRPs, confirming a conjecture from earlier versions of this work. Our findings lead to new design requirements for secure electrical Strong PUFs, and will be useful to PUF designers and attackers alike. <s> BIB004 </s> Hardware Security For and Beyond CMOS Technology: An Overview on Fundamentals, Applications, and Challenges <s> Physically-Unclonable Functions (PUFs) <s> Severe security threats and alerts associated with the use of smart devices have drawn increasing public attentions since the inception of Internet of Things (IoT) in late 1990s. IoT devices pose a unique and challenging scenario for hardware security because of their ubiquity and area-power cost constraints. Traditional software techniques and established cryptographic methods are either inadequate or impractical due to the computational capacity and permanent storage required to process and maintain the privacy of the secret key. In this light, Physical Unclonable Function (PUF), a burgeoning technology rooted in 2002, comes in handy as an inexpensive and yet effective security primitive to overcome the forgery tagging problem by its radically different way of generating and processing secret keys in security hardware. PUFs are hardware structures or functions designed to utilize the physical disorder of random nanoscale phenomena for the derivation of keys without having to keep any security-critical information explicitly in hardware. As we usher PUF into its 15th anniversary in 2017, it is timely to review the advancements of PUF over the past decade. Specifically, this survey addresses three fundamental questions which are at all times relevant in the security arms race. These questions are: how secure can a PUF be? what differences have PUFs brought to security applications and how do these differences impact existing security protocols? how is hardware implementation research influenced by the opportunities of nanotechnologies and new discoveries of disorder-based physical phenomena? It is hoped that this retrospective study of problems and solutions encountered in the journey of developing PUF to its current state will foreshadow the challenges and opportunities for future sustainable activities in the field. <s> BIB005 </s> Hardware Security For and Beyond CMOS Technology: An Overview on Fundamentals, Applications, and Challenges <s> Physically-Unclonable Functions (PUFs) <s> Physical unclonable functions (PUFs) serve as a hardware source of private information that cannot be duplicated and have applications in hardware integrity and information security. Here we demonstrate a photonic PUF based on ultrafast nonlinear optical interactions in a chaotic silicon micro-cavity. The device is probed with a spectrally-encoded ultrashort optical pulse, which nonlinearly interacts with the micro-cavity. This interaction produces a highly complex and unpredictable, yet deterministic, ultrafast response that can serve as a unique “fingerprint” of the cavity and as a source of private information for the device’s holder. Experimentally, we extract 17.1-kbit binary keys from six different photonic PUF designs and demonstrate the uniqueness and reproducibility of these keys. Furthermore, we experimentally test exact copies of the six photonic PUFs and demonstrate their unclonability due to unavoidable fabrication variations. <s> BIB006 </s> Hardware Security For and Beyond CMOS Technology: An Overview on Fundamentals, Applications, and Challenges <s> Physically-Unclonable Functions (PUFs) <s> The promise of strong physical unclonable functions (PUF) is to utilize the manufacturing variations of circuit elements to produce an independent and unpredictable response to any input challenge vector. Attacks on PUFs that predict the responses to input challenge vectors offer an interesting research problem. An attacking approach based on the optimization theory and side-channel information is proposed where we estimate the manufacturing variations of the circuit elements and predict the PUF’s responses to challenge vectors whose actual responses are not known. We apply this attacking approach on some popular PUF designs, including the Arbiter PUFs, the Memristor Crossbar PUFs, and the XOR Arbiter PUFs. Simulations show a substantial reduction in attack complexity compared with previously proposed machine-learning (ML)-based attacks: we achieve an average reduction of 66% in attack time compared with the ML approach. Despite some overhead, our approach is also applicable when the PUF responses are noisy. <s> BIB007 </s> Hardware Security For and Beyond CMOS Technology: An Overview on Fundamentals, Applications, and Challenges <s> Physically-Unclonable Functions (PUFs) <s> The omnipresent digitalization trend has enabled a number of related malicious activities, ranging from data theft to disruption of businesses, counterfeiting of devices, and identity fraud, among others. Hence, it is essential to implement security schemes and to ensure the reliability and trustworthiness of electronic circuits. Toward this end, the concept of physically unclonable functions (PUFs)has been established at the beginning of the 21st century. However, most PUFs have eventually, at least partially, fallen short of their promises, which are unpredictability, unclonability, uniqueness, reproducibility, and tamper resilience. That is because most PUFs directly utilize the underlying microelectronics, but that intrinsic randomness can be limited and may thus be predicted, especially by machine learning. Optical PUFs, in contrast, are still considered as promising—they can derive strong, hard-to-predict randomness independently from microelectronics, by using some kind of “optical token.” Here, we propose a novel concept for plasmonics-enhanced optical PUFs, or peo-PUFs in short. For the first time, we leverage two highly nonlinear phenomena in conjunction by construction: first, light propagation in a silicon disk resonator, and second, surface plasmons arising from nanoparticles arranged randomly on top of the resonator. We elaborate on the physical phenomena, provide simulation results, and conduct a security analysis of peo-PUFs for secure key generation and authentication. This study highlights the good potential of peo-PUFs, and our future work is to focus on fabrication and characterization of such PUFs. <s> BIB008
. When applied some input stimulus, a PUF should provide a fully de-correlated output response. This response should be reproducible for the very same PUF, even under varying environmental conditions, but it must differ across different PUF instances, even for the same PUF design. PUFs are used for (i) "fingerprinting" or authentication of hardware or (ii) challenge-response-based security schemes  BIB003 BIB005 . Desired properties for PUFs are uniqueness, unclonability, unpredictability, reproducibility, and tamper resilience. Electronic PUFs represent the dominant class of PUFs, with prominent types of electronic PUFs using ring oscillators, arbiters, bistable rings, and memories  BIB003 BIB005  . The core principle for such PUFs is to leverage the process variations inherent to (CMOS) fabrication, through various dedicated circuitry. However, the resulting randomness is limited for most PUF implementations; it may be machine-learned and, thus, cloned BIB005  BIB004 BIB007 . Optical PUFs represent another interesting class BIB003 BIB001  BIB002 BIB006 BIB008 . Here the idea is to manufacture an "optical token" which, in addition to structural variations inherently present in selected optical media, may contain randomly included materials, e.g., nanoparticles. Depending on the materials used for the token and the inclusions as well as the design of the token itself, these phenomena can be highly chaotic and nonlinear by nature BIB006 BIB008 . Hence, optical PUFs are considered more powerful than electronic PUFs.