A Survey on Anonymous Communication Systems with a Focus on Dining Cryptographers Networks

Traffic analysis attacks can counteract end-to-end encryption and use the leaked communication metadata to reveal information about the communicating parties. With an ever-increasing amount of traffic by an ever-increasing amount of networked devices, this undermines communication privacy and goes against the uptrend of limiting personal data collection. Therefore, Anonymous Communication Systems (ACSs) are proposed to protect the users' privacy by hiding the relationship between transmitted messages and their senders and receivers, providing privacy properties known as anonymity, unlinkability and unobservability. This article aims to review the research in the ACSs field based on its applicability in real-world scenarios. First, we present an overview of the underlying principles of ACSs and different methods. Then, we focus on Dining Cryptographers Networks (DCNs) and the methods for anonymous communication that are based on them. We investigate the alignment of ACSs with the privacy terminologies. Most notably, the DCN-based methods are information-theoretically secure and thus provide unconditional unobservability guarantees. Their initial adoption for anonymous communications was hindered initially as their computational and communication overhead was deemed too significant at that time and scalability problems occurred. However, several more recent contributions such as the possibility to transmit arbitrary length messages, efficient handling of disruptors and improvements in overhead made the integration of modern DCN-based methods more realistic. Previous surveys on ACSs did not cover the most recent research advances in this area or did not focus on DCN-based methods. This comprehensive investigation of modern ACSs and DCN-based systems closes this gap.