Using Quantum Resources for Security and Computation

Ball, Elliott and Young, Robert (2024) Using Quantum Resources for Security and Computation. PhD thesis, Lancaster University.

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Abstract

Quantum mechanics and information theory have jointly impacted multiple fields. Two in particular are security and computing. Via the use of quantum resources, exploits in currently used digital security systems are known, whilst the theory also promises security for future systems. Quantum theory has been shown to have fundamental impacts on computing technology, but modern experimental hardware is limited in power and use cases. This thesis is concerned with developments in the use of quantum resources in both fields. Physically unclonable functions (PUFs), a static form of entropy source with uses in hardware-based cryptography, are investigated. Utilising colloidal quantum dot based ink in order to fabricate a series of optical PUF (OPUF) devices, the reliable transformation of (classical) optical information whose source’s fundamental optical properties are governed by quantum theory into a unique fingerprint for further processing in cryptographic protocols is explored. First, the ability to use only a smartphone device to both excite, and capture the optical emission of, an OPUF is explored. It is shown that these images can be reliably converted into binary keys via two algorithms. Next, a novel type of OPUF is proposed. Two inks, each comprised of quantum dots with peak emission at different wavelengths are used to fabricated a device which produces two, separable responses under a single optical challenge. The correlation between two outputs from a given device is found to be inconsistent, with the cause for such inconsistencies explored. Finally, by making use of a hybrid quantum-classical computing method, an algorithm for learning the preparation circuit of an unknown mixed state is defined. In order to combat known issues with scalability of current hardware, this work explores the possibility of reformulating the well-known Hilbert-Schmidt distance using local quantum objects. A variety of functions are investigated, with the final answer remaining open.