Popular Branchings and Their Dual Certificates

Let G be a digraph where every node has preferences over its incoming edges. The preferences of a node extend naturally to preferences over branchings, i.e., directed forests; a branching B is popular if B does not lose a head-to-head election (where nodes cast votes) against any branching. Such popular branchings have a natural application in liquid democracy. The popular branching problem is to decide if G admits a popular branching or not. We give a characterization of popular branchings in terms of dual certificates and use this characterization to design an efficient combinatorial algorithm for the popular branching problem. When preferences are weak rankings, we use our characterization to formulate the popular branching polytope in the original space and also show that our algorithm can be modified to compute a branching with least unpopularity margin. When preferences are strict rankings, we show that “approximately popular” branchings always exist.TU Berlin, Open-Access-Mittel – 202

Trustworthy Elections? Eine Übersicht aktueller Verfahren & Probleme von Internetwahlen in unkontrollierten Umgebungen

Remote electronic voting or informally called "Internet-Voting" has been subject to research for several decades and is regularly part of the public debate. A special focus is thereby on remote voting procedures in uncontrolled environments. That is, election procedures which voters can use to cast their ballot conveniently from their own computer at home. Obviously, special security requirements are put on this kind of election procedures. This paper aims to present the legal requirements of general elections demanded by the example of the German constituion and derive appropriate cryptographical, technical, and organizational properties. Based on these, a methodology to assess remote electronic voting procedures regarding specific threat models is further developed. After having presented a broad survey of productively used as well as mostly academic voting procedures, those are evaluated and comparatively presented using the formerly developed methodology. Being the prototype of elections in uncontrolled environments, the postal voting procedure currently used in Germany is also assessed in order to embed the results into the overall discussion.Internetwahlverfahren, informell "Internet-Voting" genannt, sind schon seit einigen Jahrzehnten im Fokus der Forschung und auch immer wieder Teil öffentlicher Debatten. Ein besonderes Hauptaugenmerk liegt dabei auf Internetwahlverfahren zur Nutzung in unkontrollierten Umgebungen, also Wahlverfahren, die Wählerinnen und Wähler bequem zu Hause vom eigenen Computer aus benutzen können, um ihre Stimme abzugeben. Selbstverständlich werden an Verfahren dieser Art besondere Anforderungen hinsichtlich ihrer Sicherheit gestellt. Diese Arbeit soll exemplarisch die rechtlichen Voraussetzungen vorstellen, welche vom deutschen Grundgesetz vorgegeben werden, um daraus technische, kryptografische sowie organisatorische Eigenschaften abzuleiten. Darauf aufbauend wird eine Vorgehensweise weiterentwickelt, die es ermöglichen soll, Internetwahlverfahren in unkontrollierten Umgebungen anhand spezifischer Angreifermodelle zu bewerten. Nachdem eine breite Übersicht praktisch eingesetzter sowie akademischer Verfahren vorgestellt wurde, sollen eben diese Verfahren anhand der vorher entwickelten Vorgehensweise bewertet und vergleichend dargestellt werden. Zum Abschluss wird das gegenwärtig in Deutschland eingesetzte Briefwahlverfahren, welches sozusagen die Urform von Wahlen in unkontrollierten Umgebungen darstellt, untersucht und die Ergebnisse in die Diskussion eingebettet

A comparative security analysis of the German federal postal voting process

The percentage of votes cast by postal voting increases with every election for the German federal parliament (Bundestag). However, especially compared to Internet voting, concerns regarding security, transparency, and trustworthiness of postal voting are rarely discussed. This paper outlines the established process of postal voting in Germany and evaluates it with regard to various security-relevant characteristics. For this evaluation, a methodology originally developed for Internet voting is used in order to ensure comparability. The aim is to identify weaknesses as well as potential for optimization, to compare German postal voting with selected Internet voting schemes, and to derive implications for policy and further research

Subjektive Bewertung von Verfahren der Farbsignalaufbereitung und -verarbeitung mit erweitertem Farbenraum und Konstant-Luminanz-Prinzip. Tl.1

The conventional method of generation and processing color components causes image defects, which can be avoided in a future HDTV-system: loss of sharpness and resolution by violation of the constant luminance principle, reduced color gamut and gamma adjustment which is not ideal. With the CIELAB-codec a coding procedure is introduced which avoids these deficiencies, but which has 'to be paid for' with increased hardware complexity at the receiver side. The extension of the color gamut and the observance of the constant luminance principle also has a series of effects on the noise performance of the total system. Therefore, the noise performance of several color coding procedures is theoretically analyzed as well as practically investigated by means of subjective tests with natural pictures. Suggestions are made for the selection of optimum chrominance axes and investigations are reported concerning the procedures of one- two- and three-dimensional prefiltering, subsampling and reconstruction for the chrominance components based on CIELAB-coding

Navigation dependent nonlinear depth scaling

In this paper we discuss the minimum required depth accu-racy for a typical immersive video application. We show how to apply the theory of plenoptic sampling to the case of a single reference camera. In this way we bridge the gap be-tween classical 3D warp applications and the more general plenoptic sampling theorem. From this we derive general rules for the design of a typical immersive video application scenario. We show that the accuracy of depth or disparity information can be adapted very precisely to the applica-tion. In this way we provide a solution for the scalability of depth map designs in dependency of application scenarios, i.e. the scalability of navigation range of the virtual camera or the scalability of the image resolution in dependency of depth resolution

Fast and Robust Shadow Detection in Videoconference Applications

A new approach for real-time shadow detection and elimination is presented. In contrast to existing methods, hue and saturation is approximated in the YUV-colour space straight away. We show the linear influence of shadow to the YUV-values and exploit this behaviour in a fast decision scheme. The proposed method is robust and capable for real-time video processing without any need of colour space transformations