Ersetzen künftig «Verifiable Credentials» X.509-Zertifikate?

X.509-Zertifikate gibt es schon seit über 40 Jahren. Sie werden für die Identifikation von Subjekten (Web-Servern, Personen, usw.) verwendet. Sie gelten als vertrauenswürdige und erprobte Berechtigungsnachweise und wir verlassen uns tagtäglich auf sie. Warum also mit Verifiable Credentials (VC) eine neue, in der breiten Öffentlichkeit unbekannte Technologie einführen? Um eine Public Key Infrastruktur (PKI) Lösung (welche auf X.509-Zertifikaten beruht) mit einer Self-Sovereign Identity (SSI) Lösung vergleichen zu können, muss zuerst der Unterschied und die Eigenschaften ihrer Berechtigungsnachweise beleuchtet werden

Was ein zeitgemässes Identitätsmanagement-System erfüllen soll

Mit zunehmenden Datenschutzforderungen wird es immer wichtiger, die Datensouveränität der Benutzer stärker zu berücksichtigen. Daher werden beim Identitätsmanagement benutzerzentrierte Ansätze diskutiert, die neben der Sicherheit des Gesamtsystems auch den Schutz der Privatsphäre der Benutzer gewährleisten. Ein Identitätsinhaber soll einem prüfenden Dienst so wenig Informationen wie möglich preisgeben und zudem soll kein weiterer Dienst Daten über die Aktivitäten eines Inhabers sammeln können. Aber was bedeutet dies für den Inhaber? Was muss ein Herausgeber von Berechtigungsnachweisen berücksichtigen, wenn er diese ausstellt? Was sind umgekehrt die Anforderungen eines prüfenden Dienstes? In diesem Artikel werden die Ansprüche von Aussteller, Inhaber und prüfendem Dienst gegenübergestellt

Optical Flow in a Smart Sensor Based on Hybrid Analog-Digital Architecture

The purpose of this study is to develop a motion sensor (delivering optical flow estimations) using a platform that includes the sensor itself, focal plane processing resources, and co-processing resources on a general purpose embedded processor. All this is implemented on a single device as a SoC (System-on-a-Chip). Optical flow is the 2-D projection into the camera plane of the 3-D motion information presented at the world scenario. This motion representation is widespread well-known and applied in the science community to solve a wide variety of problems. Most applications based on motion estimation require work in real-time; hence, this restriction must be taken into account. In this paper, we show an efficient approach to estimate the motion velocity vectors with an architecture based on a focal plane processor combined on-chip with a 32 bits NIOS II processor. Our approach relies on the simplification of the original optical flow model and its efficient implementation in a platform that combines an analog (focal-plane) and digital (NIOS II) processor. The system is fully functional and is organized in different stages where the early processing (focal plane) stage is mainly focus to pre-process the input image stream to reduce the computational cost in the post-processing (NIOS II) stage. We present the employed co-design techniques and analyze this novel architecture. We evaluate the system’s performance and accuracy with respect to the different proposed approaches described in the literature. We also discuss the advantages of the proposed approach as well as the degree of efficiency which can be obtained from the focal plane processing capabilities of the system. The final outcome is a low cost smart sensor for optical flow computation with real-time performance and reduced power consumption that can be used for very diverse application domains

Evidence for a subtractive component in motion adaptation

Adaptation to a moving stimulus changes the perception of a stationary grating and also reduces contrast sensitivity to the adaptor. We determined whether the first effect could be predicted from the second. The contrast discrimination (T vs C) function for a drifting 7.5 Hz grating test stimulus was determined when observers were adapted to a low contrast (0.075) grating of the same spatial and temporal frequency, moving in either the same or the opposite direction as the test. The effect of an adaptor moving in the same direction was to move the T vs C function upwards and to the right, in a manner consistent with an increase in divisive inhibition. We also measured the effect of adaptation on the motion-null point for a counterphasing grating containing two components, one moving in the same direction as the adaptor and the other in the opposite direction. Adaptation increased the amount of contrast of the adapted component required to achieve the motion-null point. However, this shift could not be predicted from the effects of adaptation on contrast sensitivity. In particular, the balance point was shifted in gratings of high contrast where there was no effect of adaptation on contrast discrimination. We suggest that adaptation has a subtractive (recalibration) effect in addition to its effects on the contrast transduction function, and that this subtractive effect may explain the movement after-effect seen with stationary tests

Neuronal processing of translational optic flow in the visual system of the shore crab Carcinus maenas

This paper describes a search for neurones sensitive to optic flow in the visual system of the shore crab Carcinus maenas using a procedure developed from that of Krapp and Hengstenberg. This involved determining local motion sensitivity and its directional selectivity at many points within the neurone's receptive field and plotting the results on a map. Our results showed that local preferred directions of motion are independent of velocity, stimulus shape and type of motion (circular or linear). Global response maps thus clearly represent real properties of the neurones' receptive fields. Using this method, we have discovered two families of interneurones sensitive to translational optic flow. The first family has its terminal arborisations in the lobula of the optic lobe, the second family in the medulla. The response maps of the lobula neurones (which appear to be monostratified lobular giant neurones) show a clear focus of expansion centred on or just above the horizon, but at significantly different azimuth angles. Response maps such as these, consisting of patterns of movement vectors radiating from a pole, would be expected of neurones responding to self-motion in a particular direction. They would be stimulated when the crab moves towards the pole of the neurone's receptive field. The response maps of the medulla neurones show a focus of contraction, approximately centred on the horizon, but at significantly different azimuth angles. Such neurones would be stimulated when the crab walked away from the pole of the neurone's receptive field. We hypothesise that both the lobula and the medulla interneurones are representatives of arrays of cells, each of which would be optimally activated by self-motion in a different direction. The lobula neurones would be stimulated by the approaching scene and the medulla neurones by the receding scene. Neurones tuned to translational optic flow provide information on the three-dimensional layout of the environment and are thought to play a role in the judgment of heading

A predictive focus of gain modulation encodes target trajectories in insect vision

Published: 25 July 2017When a human catches a ball, they estimate future target location based on the current trajectory. How animals, small and large, encode such predictive processes at the single neuron level is unknown. Here we describe small target-selective neurons in predatory dragonflies that exhibit localized enhanced sensitivity for targets displaced to new locations just ahead of the prior path, with suppression elsewhere in the surround. This focused region of gain modulation is driven by predictive mechanisms, with the direction tuning shifting selectively to match the target's prior path. It involves a large local increase in contrast gain which spreads forward after a delay (e.g. an occlusion) and can even transfer between brain hemispheres, predicting trajectories moved towards the visual midline from the other eye. The tractable nature of dragonflies for physiological experiments makes this a useful model for studying the neuronal mechanisms underlying the brain's remarkable ability to anticipate moving stimuli.Steven D Wiederman, Joseph M Fabian, James R Dunbier, David C O'Carrol

Multi-camera real-time three-dimensional tracking of multiple flying animals

Automated tracking of animal movement allows analyses that would not otherwise be possible by providing great quantities of data. The additional capability of tracking in real time—with minimal latency—opens up the experimental possibility of manipulating sensory feedback, thus allowing detailed explorations of the neural basis for control of behaviour. Here, we describe a system capable of tracking the three-dimensional position and body orientation of animals such as flies and birds. The system operates with less than 40 ms latency and can track multiple animals simultaneously. To achieve these results, a multi-target tracking algorithm was developed based on the extended Kalman filter and the nearest neighbour standard filter data association algorithm. In one implementation, an 11-camera system is capable of tracking three flies simultaneously at 60 frames per second using a gigabit network of nine standard Intel Pentium 4 and Core 2 Duo computers. This manuscript presents the rationale and details of the algorithms employed and shows three implementations of the system. An experiment was performed using the tracking system to measure the effect of visual contrast on the flight speed of Drosophila melanogaster. At low contrasts, speed is more variable and faster on average than at high contrasts. Thus, the system is already a useful tool to study the neurobiology and behaviour of freely flying animals. If combined with other techniques, such as ‘virtual reality’-type computer graphics or genetic manipulation, the tracking system would offer a powerful new way to investigate the biology of flying animals