Scattering-Based Methods for Holographic Detection and Encryption
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| Publicado en: | ProQuest Dissertations and Theses (2025) |
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| Acceso en línea: | Citation/Abstract Full Text - PDF |
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| Resumen: | The encryption of sensitive information—including passwords, barcodes, images, signatures, fingerprints, and other biometric data—along with the real-time validation and identification of individuals, products, packages, and documents like passports and credit cards, is of critical importance in banking, commerce, homeland security, and other fields. Conventional encryption methods rely mainly on mathematical encryption, which depends, in turn, on the presumed difficulty of solving an associated decryption problem such as factoring large prime numbers or solving an inverse problem involving discrete logarithms. While these approaches have been the foundation of modern cryptography, they are inherently susceptible to brute-force attacks, algorithmic improvements, and the advent of quantum computing, which threatens to break many traditional encryption schemes. In the past decade, an alternative approach, namely physical layer security, has been gaining a lot of attention. Unlike conventional encryption, which depends on mathematical complexity, physical security leverages the unique response of physical systems to encode information in ways that are inherently difficult to decipher or decode without access to the exact physical medium required for that purpose. This methodology thus relies on the high sensitivity of the response to small systemic changes as well as the unique signatures or fingerprints of every physical medium. This ensures that without the correct system, decryption becomes virtually impossible, thereby keeping data secure, as desired. Thus this approach takes advantage of nature’s inherent complexity. Within the optical imaging regime, which is the focus of this investigation, it also brings additional ultrafast analog computing and real-time encryption and decryption capabilities, alongside a myriad of structural or configurational variants, all of which further assures the sought-after information security.This dissertation investigates new optical scattering-based approaches for holographic encryption and detection. The underlying theme of all the developed methods and algorithms is the involvement of complex multiple scattering media, for encryption associated to both storage and communication channels, as well as for the demonstration of related enabling functions including change detection, target tracking and wavefield imaging in such complex media. The dissertation comprises fundamental contributions in four closely related areas: 1) scattering-based encryption, 2) secure scattering-based cloud computing, 3) fundamental scattering theory in complex and random media, and 4) detection, tracking, and imaging of particles in complex and random media. In the first part of this research, a new scattering-based encryption method is introduced, utilizing a reconfigurable micro-medium to guarantee that the stored signal or image can only be retrieved with the physical presence of the same medium. Next, we derive a new approach for the holographic encryption of signals, termed “differential sensing”, which is based on the encoding of wave information in the scattered field due to a complex scatterer that is embedded in a complex and random optical background. The proposed approach is coherent and thus relies on holography for both the launching of the desired probing fields as well as for the sensing itself, for which a number of holographic measurement techniques are proposed. In this methodology the cryptographic key is formed by two complex and random media and is thus harder to find than in the conventional single-medium approach, thereby rendering enhanced security. In addition, new methods based on wavefield nulling are also introduced, which enable the secure retrieval and communication of big data blocks in real time.The second part of the dissertation considers a more general class of complex and random optical systems that are dynamically varying and can be shared, as a resource, among multiple users, for cloud computing and encryption purposes. To enhance the security of such systems, we address their vulnerability to learning-based attacks that exploit ciphertext-plaintext pairs to model and reverse-engineer the scattering medium’s response, enabling unauthorized decryption without the physical medium. This enhancement is important for envisioned applications in multiuser channels that may potentially employ the same encryption system, e.g., for cloud computing and similar applications. We demonstrate the feasibility of utilizing dynamic scattering matrices for the secure encryption of information such as images uploaded by and communicated to multiple users employing the same encryption server. In this scheme, each user is assigned a unique combination of scattering matrices with specific coefficients. This approach makes it significantly hard for attackers to break the encryption, in comparison with more conventional architectures where all users rely on a single static scattering matrix per encryption block. The proposed dynamic evolution of scattering matrices, including shuffling effects, further strengthens the associated encryption security in the envisaged multiuser environments. The third and fourth parts of the thesis are related, comprising 1) fundamental wave scattering theory, and 2) its applications for the problems of 1) detecting medium’s changes and 2) imaging and tracking objects that are embedded in complex and random media. A new theory of the fundamental optical theorem for electromagnetic fields is developed that highlights the multiplicity of optical theorem detectors and paves the way for practical realizations of such detectors in different topologies and geometries. This includes planar aperture realizations which are the basis of the optical-theorem-based holographic detectors developed in this dissertation. The derived optical-theorem-inspired holographic approach is relevant for detecting and tracking particles in the vicinity of complex multiple scattering environments. Generalizations of the classical optical theorem are developed that apply to complex media. The formulation renders alternative viable forms of physically-realizable sensors capable of measuring the extinction cross section of a scatterer upon excitation with rather arbitrary wavefields. The formulation includes all the relevant multiple scattering interactions. These theoretical results are applied to the problem of detecting medium’s changes, where the measured extinction cross section is regarded as physical indicator of a target or particle’s presence in the region of interest. This technique renders, within a lens-based holographic imaging architecture, a novel form of “in situ compressive detector”, for the detection of changes using a single-pixel camera or bucket detector. The proposed methodology is adaptive, to the complex medium, which is integral to the sensing apparatus, and thereby enables constant monitoring, through progressive adaptation. Moreover, the same developed lens-based holographic system for change detection also naturally lends itself for imaging and tracking functions, with applicability in dynamically-varying media. By leveraging the holographic nature of the approach, the system not only detects and tracks particles but also provides real-time imaging capabilities, enabling the continuous monitoring of objects moving through the region under observation. The proposed technology presents significant potential for the detection of concealed threats, stealth objects, and dynamically shifting targets in complex regions. In addition, the derived methodology also enables the development of customized sensors that leverage a controllable complex multiple scattering medium and the derived holographic sensing technology for real-time particle detection and tracking. The latter context is relevant in envisioned applications in air quality control and in the detection of aerosolized biological substances including biohazard particles. The final chapter of the dissertation provides new applications of the optical theorem for detection and imaging of time-varying objects. This is an important related framework for envisioned generalizations of the developed detection and encryption methods to time-varying media. The derived theory, methods, and algorithms developed in this dissertation are thoroughly demonstrated with the help of computer simulations in two-dimensional and three-dimensional spaces, which include all the critical multiple scattering effects. |
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| ISBN: | 9798291585573 |
| Fuente: | ProQuest Dissertations & Theses Global |