Traffic analysis attacks can counteract end-to-end encryption and use leaked communication metadata to reveal information about communicating parties. With an ever-increasing amount of traffic by an ever-increasing number of networked devices, communication privacy is undermined. Therefore, Anonymous Communication Systems (ACSs) are proposed to hide the relationship between transmitted messages and their senders and receivers, providing privacy properties known as anonymity, unlinkability, and unobservability. This article aims to review research in the ACSs field, focusing on Dining Cryptographers Networks (DCNs). The DCN-based methods are information-theoretically secure and thus provide unconditional unobservability guarantees. Their adoption for anonymous communications was initially hindered because their computational and communication overhead was deemed significant at that time, and scalability problems occurred. However, more recent contributions, such as the possibility to transmit messages of arbitrary length, efficient disruption handling and overhead improvements, have made the integration of modern DCN-based methods more realistic. In addition, the literature does not follow a common definition for privacy properties, making it hard to compare the approaches' gains. Therefore, this survey contributes to introducing a harmonized terminology for ACS privacy properties, then presents an overview of the underlying principles of ACSs, in particular, DCN-based methods, and finally, investigates their alignment with the new harmonized privacy terminologies. Previous surveys did not cover the most recent research advances in the ACS area or focus on DCN-based methods. Our comprehensive investigation closes this gap by providing visual maps to highlight privacy properties and discussing the most promising ideas for making DCNs applicable in resource-constrained environments.

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ZusammenfassungDurch die pandemische Lage sind viele Lehrangebote nicht in ihrer ursprünglichen Form durchführbar. Im hier vorgestellten Fall soll das Programmieren einer Hardware-Entwicklungsplattform für das Internet der Dinge (IoT) erlernt werden. Die Studierenden arbeiten in Arbeitsgruppen mit bis zu fünf Teilnehmern. In der dezentralen Lehre ist dies nur schwer umsetzbar. Im vorliegenden Fall hätten dann drei Geräte pro Teilnehmer ausgegeben werden müssen. Ein Austausch innerhalb der Projektgruppen war zunächst nur eingeschränkt per Videokonferenz möglich. Das fragliche IoT-Labor wurde deshalb in eine virtuelle Umgebung integriert, so dass dort in Gruppen programmiert werden kann, während die IoT-Hardware mittels Video in Echtzeit beobachtet wird. Die geschaffene Lehrumgebung vereint die Durchführung von Vorlesungen, Übungen, Tutorien und Arbeitsgruppentreffen. Die Möglichkeiten zur Interaktion erleichtern es den Studierenden unter anderem, während der Vorlesung in Kontakt miteinander zu treten.