arXiv subjects

Karl W. Koch

Publications and source records attributed to Karl W. Koch.

5 recordsLinked to original sources

arXiv2025

QoeSiGN: Towards Qualified Collaborative eSignatures

eSignatures ensure data's authenticity, non-repudiation, and integrity. EU's eIDAS regulation specifies, e.g., advanced and qualified (QES) eSignatures. While eSignatures' concrete legal effects depend on the individual case, QESs constitute the highest level of technical protection and authenticity under eIDAS. QESs are based on a qualified certificate issued by a qualified trust service provider (QTSP). Despite legal requirements, technically, a QTSP represents a single point of failure. Contrary, privacy-preserving collaborative computations (P2C2s) have become increasingly practical in recent years; yet lacking an extensive investigation on potential integrations in the QES landscape. We perform a threat analysis on the QES-creation process of Austria's national eID, using STRIDE and a DREAD-like model to extract requirement challenges (RCs) primarily related to: (1) Distributed Service Robustness, (2) Agile Crypto Deployment, and (3) Active User Involvement. To address these RCs, we present QoeSiGN, utilizing novel P2C2 technologies. While currently no P2C2 addresses all RCs, legal aspects, and practical efficiency simultaneously, QoeSiGN gives instantiation possibilities for different needs. For instance, "Multi-Party HSMs" for distributed hardware-secured computations; or secure multi-party computation (software) for highest crypto agility and user involvement, where the user participates in the QES computation. Deployment-wise, QTSPs would need to adapt the signing process and setup trusted communication channels. Legal-wise, QoeSiGN's implementation appears permissible, needing further analysis for realization. Technically, QoeSiGN addresses some regulation requirements better than the current solution, such as "sole control" or crypto agility. Our identified threats and extracted requirements can be transferred to the general QES ecosystem.

cs.CR↗

arXiv2019

Disordered Anderson Localization Optical Fibers for Image Transport - A Review

Disordered optical fibers show novel waveguiding properties, enabled by the transverse Anderson localization of light, and are used for image transport. The strong transverse scattering from the transversely disordered refractive index structure results in transversely confined modes that can freely propagate in the longitudinal direction. In some sense, an Anderson localization disordered fiber behave like a large-core multimode optical fiber, with the advantage, that most modes are highly localized in the transverse plane, so any point in the cross section of the fiber can be used for localized beam transport. This property has been used for high-quality transportation of intensity patterns and images in these optical fibers. This review covers the basics and the history of the transverse Anderson localization in disordered optical fibers and captures the recent progress in imaging applications using these optical fibers.

physics.optics↗

arXiv2013

Image transport through a disordered optical fiber mediated by transverse Anderson localization

Transverse Anderson localization of light allows localized optical-beam-transport through a transversely-disordered and longitudinally-invariant medium. Its successful implementation in disordered optical fibers recently resulted in the propagation of localized beams of radii comparable with that of conventional optical fibers. We present what is, to the best of our knowledge, the first demonstration of optical image transport using transverse Anderson localization of light. The image transport quality obtained in the polymer disordered optical fiber is comparable with or better than some of the best commercially available multicore image fibers with less pixelation and higher contrast. It is argued that considerable improvement in image transport quality can be obtained in a disordered fiber made from a glass matrix with near wavelength-size randomly distributed air-holes with an air-hole fill-fraction of $50\%$. Our results open the way to device-level implementation of the transverse Anderson localization of light with potential applications in biological and medical imaging.

physics.optics↗

arXiv2013

A modal perspective on the transverse Anderson localization of light in disordered optical lattices

We frame the transverse Anderson localization of light in a one-dimensional disordered optical lattice in the language of localized propagating eigenmodes. The modal analysis allows us to explore localization behavior of a disordered lattice independent of the properties of the external excitation. Various localization-related phenomena, such as the periodic revival of a propagating Anderson-localized beam are easily explained in modal language. We characterize the localization strength by the average width of the guided modes and carry out a detailed analysis of localization behavior as a function of the optical and geometrical parameters of the disordered lattice. We also show that in order to obtain a minimum average mode width, the average width of the individual random sites in the disordered lattice must be larger than the wavelength of the light by approximately a factor of two or more, and the optimum site width for the maximum localization depends on the design parameters of the disordered lattice.

physics.optics↗

arXiv2013

Multiple-beam Propagation in an Anderson Localized Optical Fiber

We investigate the simultaneous propagation of multiple beams in a disordered Anderson localized optical fiber. The profiles of each beam fall off exponentially, enabling multiple channels at high-density. We examine the influence of fiber bends on the movement of the beam positions, which we refer to as drift. We investigate the extent of the drift of localized beams induced by macro-bending and show that it is possible to design Anderson localized optical fibers that can be used for practical beam-multiplexing applications.

physics.optics↗