Alexander Heß

Dining-cryptographers networks (DCN) can achieve information-theoretical privacy. Unfortunately, they are not well suited for peer-to-peer networks as they are used in blockchain applications to disseminate transactions and blocks among par- ticipants. In previous but preliminary work, we proposed a three- phase approach with an initial phase based on a DCN with a group size of k while later phases take care of the actual broadcast within a peer-to-peer network. This paper describes our DCN protocol in detail and adds a performance evaluation powered by our proof-of-concept implementation. Our contributions are (i) an extension of the DCN protocol by von Ahn for fair delivery of arbitrarily long messages sent by potentially multiple senders, (ii) a privacy and security analysis of this extension, (iii) various performance optimisation especially for best-case operation, and (iv) a performance evaluation. The latter uses a latency of 100 ms and a bandwidth limit of 50 Mbit s−1 between participants. The interquartile range of the largest test of the highly secured version took 35s ± 1.25s for a full run. All tests of the optimized common-case mode show the dissemination of a message within 0.5s ± 0.1s. These results compare favourably to previously established protocols for k-anonymous transmission of fixed size messages, outperforming the original protocol for messages as small as 2 KiB.

Graceful degradation is an established concept to improve the resilience of systems, especially when other resilience mechanisms have failed. Its implementation is often heavily tied to the application code and, thus, cumbersome and error prone. As IoT systems get not only ubiquitous but also critical, reliable graceful degradation would be ideal. In this paper, we present the Morpheus framework that provides a TypeScript-internal DSL to enable a systematic development of degradable IoT systems. The design of the framework is based on the concept of separation of concerns by providing distinct yet linked languages to specify hierarchical components and their connections; the components’ operating modes and transfer functions between them; as well as state machines for the specification of the components’ behaviour in each operating mode. The operating modes for each component serve as degradation levels. Automatic degradation of a component is triggered in case of failures of connected components. With recovery from underlying failures, the component is automatically upgraded back to a higher level. We illustrate our framework using a simplified prototype of an entrance barrier of a parking garage