" In this dissertation we explore a new paradigm emerging from the subtleties of cryptographic implementations and relating to theoretical aspects of cryptography. This new paradigm, namely physical variables (PVs), simply describes properties of physical objects designed to be identical but are not due to manufacturing variability. In the first part of this dissertation, we focus our attention on scenarios which require the unique identification of physical objects and we show how Gaussian PVs can be used to fulfill such a requirement. Using this framework we present and analyze a new technique for fingerprinting compact discs (CDs) using the manufacturing variability found in the length of the CDs' lands and pits. Although the variability measured is on the order of 20 nm, the technique does not require the use of microscopes or any advanced equipment. Instead, the electrical signal produced by the photo-detector inside the CD reader will be sufficient to measure the desired variability. We thoroughly investigate the new technique by analyzing data collected from 100 identical CDs and show how to extract a unique fingerprint for each CD. In the second part, we shift our attention to physically parameterized functions (PPFs). Although all the constructions we provide are centered around delay-based physically unclonable functions (PUFs), we stress that the use of the term PUF could be misleading as most circuits labeled with the term PUF are in reality clonable on the protocol level. We argue that using a term like PPFs to describe functions parameterized by a PV is a more accurate description. Herein, we thoroughly analyze delay-PUFs and use a mathematical framework to construct two authentication protocols labeled PUF-HB and HB+PUF. Both these protocols merge the known HB authentication family with delay-based PUFs. The new protocols enjoy the security reduction put forth by the HB portion of the protocol and at the same time maintain a level of hardware security provided by the use of PUFs. We present a proof of concept implementation for HB+PUF which takes advantage of the PUF circuit in order to produce the random bits typically needed for an HB-based authentication scheme. The overall circuit is shown to occupy a few thousand gates. Finally, we present a new authentication protocol that uses 2-level PUF circuits and enables a security reduction which, unlike the previous two protocols, stems naturally from the usage of PVs. "

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Physical Unclonable Functions are a unique class of circuits that leverage the inherentvariations in manufacturing process to create unique,unclonableIDs and secret keys.The distinguishing feature of PUFs is that even an untrusted foundry cannot create a copy of the circuit as it is impossible to control the manufacturing process variations.PUFs can operate reliably in presence of voltage and temperature variations. In thisthesis, weexplorethe security offered by PUFs and tradeoffs between different metrics such as uniqueness, reliability and energy consumption.Benefits of sub-threshold PUF operation and the use of delay based Arbiter PUFs and ring oscillator PUFs in low power applications is evaluated. As we scale into lower technology nodes, there exists sufficient inter chip variation that enables each IC to be identified securely.The impact of scaling on the identification capabilities of a PUF and its reliability has been demonstrated in this work by analyzing the behavior of an Arbiter PUF in 45nm, 32nm and 22nm technology nodes. Further,the Arbiter PUF design has been implemented on a test-chip and fabricated using 45nm industry models andresults from post silicon validation are presented. Finally, we investigate a new class of PUF circuits in this work, that provide better security against machine learning based software modeling attacks. The strong identification capabilities and sufficiently high reliability offered by these PUF circuits make them promising candidates for future applications requiring securehardware cryptographic primitives.

Physically unclonable functions are increasingly used as security primitives for device identification and anti-counterfeiting. However, PUFs are associated with noise and bias which in turn affects its property of reliability and predictability. The noise is corrected using fuzzy extractors, but the helper data generated during the process may cause leakage in min-entropy due to the bias observed in the response. This thesis offers two optimization techniques for PUF based protocols. The first part talks about the construction of a secure enrollment solution for PUFs on a low-end resource-constrained device using a microcontroller and a secure networked architecture. The second part deals with the combined optimization of min-entropy and error-rate using symbol clustering techniques to improve the reliability of SRAM PUFs. The results indicate an increase in min-entropy without much effect on the error rate but at the expense of PUF size. / Master of Science