This dissertation presents work carried out in collaboration with the IMDEA nanoscience institute. We study the recently proposed quantum confinement physically unclonable function by Roberts, et al. that utilises resonant tunnelling diodes (physical representation of a quantum well) and atomic scale imperfections for applications in cryptography and identification. Presently such entities rely on their resonance peak position as the basis for a new approach to electronic identification systems.By solely relying on the resonance peak of these devices deconvolution outputs an average of 8 bits per device, concatenation of up to 16 devices outputs a satisfactory number of bits for applications in uniqueness. However we explore the possibility of increasing the bit density of such physically unclonable functions that range from tangibly modifying the heterostructure with the use of a focused ion beam to induce quantum effects of 1 dimension (quantum wire) and 0 dimension (quantum dot) that would manifest its self as multiple resonance peaks observed on the current/voltage characteristic.Our findings show multiple devices with consistent new features as a result of modification with the focused ion beam ultimately increasing the bit density. We carry out cryogenic measurements and comment on the fact that such features are not supported by previous work studying resonant tunnelling in the 1 & 0 states of double barrier heterostructures.
This dissertation presents work carried out in collaboration with the IMDEA nanoscience institute. We study the recently proposed quantum confinement physically unclonable function by Roberts, et al. that utilises resonant tunnelling diodes (physical representation of a quantum well) and atomic scale imperfections for applications in cryptography and identification. Presently such entities rely on their resonance peak position as the basis for a new approach to electronic identification systems.By solely relying on the resonance peak of these devices deconvolution outputs an average of 8 bits per device, concatenation of up to 16 devices outputs a satisfactory number of bits for applications in uniqueness. However we explore the possibility of increasing the bit density of such physically unclonable functions that range from tangibly modifying the heterostructure with the use of a focused ion beam to induce quantum effects of 1 dimension (quantum wire) and 0 dimension (quantum dot) that would manifest its self as multiple resonance peaks observed on the current/voltage characteristic.Our findings show multiple devices with consistent new features as a result of modification with the focused ion beam ultimately increasing the bit density. We carry out cryogenic measurements and comment on the fact that such features are not supported by previous work studying resonant tunnelling in the 1 & 0 states of double barrier heterostructures.
Physical unclonable functions (PUFs) are physical components that translate an input challenge into a unique response that cannot be predicted without access to the component itself. PUFs can integrated into devices to ensure trust in everyday interactions and to act as a defence; guarding against the counterfeiting of goods by providing robust identities. In the past these functions have relied on classical phenomena, including signal speed through a ‘race’ wire (Arbiter PUFs [1]) or probabilistic switching of electronic latches. Many PUFs have been found to be vulnerable to response modelling [2] or direct cloning [3] attacks, and have limitations on minimum size. These vulnerabilities and constraints prompt turning away from classical PUF methodologies and towards architectures exploiting quantum phenomena, such as quantum confinement. We propose a PUF concept that operates on the principles on quantum confinement through the fluctuation of the first energy level of a resonant tunnelling diode (RTD) [4]. These fluctuations derive from intrinsic atomic scale variations in the manufacture of each RTD, and cause macroscopic changes in the specific electronic characteristics of the device [5]. In the simplest form, uniqueness in the RTDs would be derived from the current and voltage of the maximum tunnelling current position (see figure 1a) of each device. To be used as the constituent of a PUF, each resonant tunnel diode should be unique from one another, and stable after repeated readings. We compared the current and voltage of this peak current position of 26 RTDs that could constitute the PUF. It was found that the peaks of each RTD do not overlap to a certainty of 99.997% (see figure 1b). The stability of repeat measurements of a single device was also examined, finding a deviation upon repeat readings of two standard deviations (95%) compared to the average current and voltage values (figure 1c). This analysis suggests that the resonant tunnelling diode is a strong candidate for use in the next generation of more secure, quantum derived security hardware.
The unrelenting advancement of modern technology has inadvertently allowed the production of counterfeit components to become increasingly cheaper and easier, undermining the trust of everyday interactions and communications. An emerging solution to this problem is the use of physically unclonable functions1 (PUFs) - physical devices with random characteristics locked into their structure at the point of fabrication. The application of a stimulus to these constructions results in a hard-to-predict response due to the interaction with the complex microstructure of the device. This response is then used as a 'fingerprint' that can be used for a given application. Among others, these include low-cost device identification and authentication, secure key generation and the binding of software to hardware platforms. However, traditional PUFs have various setbacks: they suffer from not being truly unclonable, are susceptible to sophisticated attacks and bear a risk of emulation and simulation. Here we show that quantum physics lends itself to the provision of unique identities in the form of fluctuations in measurements of resonant tunnelling diodes (RTDs) containing various nanostructures. An example of which is a quantum dot, shown in Fig. 1. This provides an uncomplicated measure of identity, without conventional resource limitations or vulnerabilities. The quantum tunnelling spectrum also shown in Fig. 1 is sensitive to the atomic structure within the RTD, with each device providing extreme uniqueness that is presently impossible to clone or simulate. This new class of authentication device, coined the quantum unclonable function (QUF)2, operate with the fewest resources in simple electronic structures operating above 300 K.
Modern technology unintentionally provides resources that enable the trust of everyday interactions to be undermined. Some authentication schemes address this issue using devices that give a unique output in response to a challenge. These signatures are generated by hard-to-predict physical responses derived from structural characteristics, which lend themselves to two different architectures, known as unique objects (UNOs) and physically unclonable functions (PUFs). The classical design of UNOs and PUFs limits their size and, in some cases, their security. Here we show that quantum confinement lends itself to the provision of unique identities at the nanoscale, by using fluctuations in tunnelling measurements through quantum wells in resonant tunnelling diodes (RTDs). This provides an uncomplicated measurement of identity without conventional resource limitations whilst providing robust security. The confined energy levels are highly sensitive to the specific nanostructure within each RTD, resulting in a distinct tunnelling spectrum for every device, as they contain a unique and unpredictable structure that is presently impossible to clone. This new class of authentication device operates with minimal resources in simple electronic structures above room temperature.
The rapid development of technology has provided a wealth of resources enabling the trust of everyday interactions to be undermined. Authentication schemes aim to address this challenge by providing proof of identity. This can be achieved by using devices that, when challenged, give unique but reproducible responses. At present, these distinct signatures are commonly generated by physically unclonable functions, or PUFs. These devices provide a straightforward measurement of a physical characteristic of their structure that has inherent randomness, due to imperfections in the manufacturing process. These hard-to-predict physical responses can generate a unique identity that can be used for authentication without relying on the secrecy of stored data. However, the classical design of these devices limits both their size and security. Here we show that the extensively studied problematic fluctuations in the current-voltage measurements of resonant tunnelling diodes (RTDs) provide an uncomplicated, robust measurement that can function as a PUF without conventional resource limitations. This is possible due to quantum tunnelling within the RTD, and on account of these room temperature quantum effects, we term such devices QUFs - quantum unclonable functions. As a result of the current-voltage spectra being dependent on the atomic structure and composition of the nanostructure within the RTD, each device provides a high degree of uniqueness, whilst being impossible to clone or simulate, even with state-of-the-art technology. We have thus created PUF-like devices requiring the fewest resources which make use of quantum phenomena in a highly manufacturable electronic device operating at room temperature. Conventional spectral analysis techniques, when applied to our QUFs, will enable reliable generation of unpredictable unique identities which can be employed in advanced authentication systems.
Modern technology unintentionally provides resources that enable the trust of everyday interactions to be undermined. Some authentication schemes address this issue using devices that give a unique output in response to a challenge. These signatures are generated by hard-to-predict physical responses derived from structural characteristics, which lend themselves to two different architectures, known as unique objects (UNOs) and physically unclonable functions (PUFs). The classical design of UNOs and PUFs limits their size and, in some cases, their security. Here we show that quantum confinement lends itself to the provision of unique identities at the nanoscale, by using fluctuations in tunnelling measurements through quantum wells in resonant tunnelling diodes (RTDs). This provides an uncomplicated measurement of identity without conventional resource limitations whilst providing robust security. The confined energy levels are highly sensitive to the specific nanostructure within each RTD, resulting in a distinct tunnelling spectrum for every device, as they contain a unique and unpredictable structure that is presently impossible to clone. This new class of authentication device operates with minimal resources in simple electronic structures above room temperature.
Physically unclonable functions, or PUFs, present a means to securely identify objects, both implicit and attached, alongside several uses in conventional secure communication techniques. Many types of PUF based on varying sources of fingerprint entropy have been suggested, and the higher-level theoretical properties and implications of this primitive have been extensively discussed. However, each different prospective implementation of PUF typically approaches the practical considerations for the conversion from a unique entropy source to ultimate PUF implementation anew. These studies typically treat the intermediate processing schema, such as response binning, solely as a means to an end rather than a subject of explicit discussion and evaluation. As such, there exist few studies into developing a general framework for the optimisation and simulation of the important elements that lie between the measurement of the particular entropy source and the evaluation of the final device as a whole. This thesis seeks to outline and validate a generalised schema for the conversion of entropy source to final results, presenting the fundamental design elements and figures of merit for the process at every stage where applicable. Further to this, each stage of the process is expressed analytically, allowing the direct derivation of the ultimate figures of merit based on the measurement outcomes of the initial source of entropy. To validate, this process is applied towards the resonant tunnelling diode (RTD) as the prospective entropic unit cell. This type of semiconductor device has several properties that make it an interesting candidate upon which to base a PUF, and this work additionally seeks to outline these benefits and enumerate the general comparative figures of merit for a PUF derived therefrom.