TY - CONF AB - We present three robust overlay networks: First, we present a network that organizes the nodes into an expander and is resistant to even massive adversarial churn. Second, we develop a network based on the hypercube that maintains connectivity under adversarial DoS-attacks. For the DoS-attacks we use the notion of a Omega(log log n)-late adversary which only has access to topological information that is at least Omega(log log n) rounds old. Finally, we develop a network that combines both churn- and DoS-resistance. The networks gain their robustness through constant network reconfiguration, i.e., the topology of the networks changes constantly. Our reconguration algorithms are based on node sampling primitives for expanders and hypercubes that allow each node to sample a logarithmic number of nodes uniformly at random in O(log log n) communication rounds. These primitives are specific to overlay networks and their optimal runtime represents an exponential improvement over known techniques. Our results have a wide range of applications, for example in the area of scalable and robust peer-to-peer systems. AU - Drees, Maximilian AU - Gmyr, Robert AU - Scheideler, Christian ID - 215 T2 - Proceedings of the 28th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA) TI - Churn- and DoS-resistant Overlay Networks Based on Network Reconfiguration ER - TY - JOUR AU - Schmid, Stefan AU - Avin, Chen AU - Scheideler, Christian AU - Borokhovich, Michael AU - Haeupler, Bernhard AU - Lotker, Zvi ID - 1835 IS - 3 JF - IEEE/ACM Trans. Netw. TI - SplayNet: Towards Locally Self-Adjusting Networks ER - TY - CONF AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - Porter, Alexandra AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1836 T2 - DNA Computing and Molecular Programming - 22nd International Conference, DNA 22, Munich, Germany, September 4-8, 2016, Proceedings TI - On the Runtime of Universal Coating for Programmable Matter VL - 9818 ER - TY - CONF AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1837 T2 - Proceedings of the 28th ACM Symposium on Parallelism in Algorithms and Architectures, SPAA 2016, Asilomar State Beach/Pacific Grove, CA, USA, July 11-13, 2016 TI - Universal Shape Formation for Programmable Matter ER - TY - CHAP AU - W. Richa, Andrea AU - Scheideler, Christian ID - 1845 T2 - Encyclopedia of Algorithms TI - Jamming-Resistant MAC Protocols for Wireless Networks ER - TY - CONF AB - We present a self-stabilizing algorithm for overlay networks that, for an arbitrary metric given by a distance oracle, constructs the graph representing that metric. The graph representing a metric is the unique minimal undirected graph such that for any pair of nodes the length of a shortest path between the nodes corresponds to the distance between the nodes according to the metric. The algorithm works under both an asynchronous and a synchronous daemon. In the synchronous case, the algorithm stablizes in time O(n) and it is almost silent in that after stabilization a node sends and receives a constant number of messages per round. AU - Gmyr, Robert AU - Lefèvre, Jonas AU - Scheideler, Christian ID - 155 T2 - Proceedings of the 18th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS) TI - Self-stabilizing Metric Graphs ER - TY - CONF AB - For overlay networks, the ability to recover from a variety of problems like membership changes or faults is a key element to preserve their functionality. In recent years, various self-stabilizing overlay networks have been proposed that have the advantage of being able to recover from any illegal state. However, the vast majority of these networks cannot give any guarantees on its functionality while the recovery process is going on. We are especially interested in searchability, i.e., the functionality that search messages for a specific identifier are answered successfully if a node with that identifier exists in the network. We investigate overlay networks that are not only self-stabilizing but that also ensure that monotonic searchability is maintained while the recovery process is going on, as long as there are no corrupted messages in the system. More precisely, once a search message from node u to another node v is successfully delivered, all future search messages from u to v succeed as well. Monotonic searchability was recently introduced in OPODIS 2015, in which the authors provide a solution for a simple line topology.We present the first universal approach to maintain monotonic searchability that is applicable to a wide range of topologies. As the base for our approach, we introduce a set of primitives for manipulating overlay networks that allows us to maintain searchability and show how existing protocols can be transformed to use theses primitives.We complement this result with a generic search protocol that together with the use of our primitives guarantees monotonic searchability.As an additional feature, searching existing nodes with the generic search protocol is as fast as searching a node with any other fixed routing protocol once the topology has stabilized. AU - Scheideler, Christian AU - Setzer, Alexander AU - Strothmann, Thim Frederik ID - 142 T2 - Proceedings of the 30th International Symposium on Distributed Computing (DISC) TI - Towards a Universal Approach for Monotonic Searchability in Self-stabilizing Overlay Networks ER - TY - JOUR AB - This paper considers the problem of how to efficiently share a wireless medium which is subject to harsh external interference or even jamming. So far, this problem is understood only in simplistic single-hop or unit disk graph models. We in this paper initiate the study of MAC protocols for the SINR interference model (a.k.a. physical model). This paper makes two contributions. First, we introduce a new adversarial SINR model which captures a wide range of interference phenomena. Concretely, we consider a powerful, adaptive adversary which can jam nodes at arbitrary times and which is only limited by some energy budget. Our second contribution is a distributed MAC protocol called Sade which provably achieves a constant competitive throughput in this environment: we show that, with high probability, the protocol ensures that a constant fraction of the non-blocked time periods is used for successful transmissions. AU - Ogierman, Adrian AU - Richa, Andrea AU - Scheideler, Christian AU - Schmid, Stefan AU - Zhang, Jin ID - 3872 IS - 3 JF - Distributed Computing SN - 0178-2770 TI - Sade: competitive MAC under adversarial SINR VL - 31 ER - TY - JOUR AU - Koutsopoulos, Andreas AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1812 JF - Inf. Comput. TI - Towards a universal approach for the finite departure problem in overlay networks ER - TY - JOUR AU - P. Fekete, Sandor AU - W. Richa, Andrea AU - Römer, Kay AU - Scheideler, Christian ID - 1813 IS - 2 JF - SIGACT News TI - Algorithmic Foundations of Programmable Matter Dagstuhl Seminar 16271 ER - TY - JOUR AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1814 JF - Theor. Comput. Sci. TI - Universal coating for programmable matter ER - TY - CONF AU - J. Daymude, Joshua AU - Gmyr, Robert AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1815 T2 - Algorithms for Sensor Systems - 13th International Symposium on Algorithms and Experiments for Wireless Sensor Networks, ALGOSENSORS 2017, Vienna, Austria, September 7-8, 2017, Revised Selected Papers TI - Improved Leader Election for Self-organizing Programmable Matter ER - TY - CONF AB - We initiate the study of network monitoring algorithms in a class of hybrid networks in which the nodes are connected by an external network and an internal network (as a short form for externally and internally controlled network). While the external network lies outside of the control of the nodes (or in our case, the monitoring protocol running in them) and might be exposed to continuous changes, the internal network is fully under the control of the nodes. As an example, consider a group of users with mobile devices having access to the cell phone infrastructure. While the network formed by the WiFi connections of the devices is an external network (as its structure is not necessarily under the control of the monitoring protocol), the connections between the devices via the cell phone infrastructure represent an internal network (as it can be controlled by the monitoring protocol). Our goal is to continuously monitor properties of the external network with the help of the internal network. We present scalable distributed algorithms that efficiently monitor the number of edges, the average node degree, the clustering coefficient, the bipartiteness, and the weight of a minimum spanning tree. Their performance bounds demonstrate that monitoring the external network state with the help of an internal network can be done much more efficiently than just using the external network, as is usually done in the literature. AU - Gmyr, Robert AU - Hinnenthal, Kristian AU - Scheideler, Christian AU - Sohler, Christian ID - 105 T2 - Proceedings of the 44th International Colloquium on Automata, Languages, and Programming (ICALP) TI - Distributed Monitoring of Network Properties: The Power of Hybrid Networks ER - TY - CONF AB - Searching for other participants is one of the most important operations in a distributed system.We are interested in topologies in which it is possible to route a packet in a fixed number of hops until it arrives at its destination.Given a constant $d$, this paper introduces a new self-stabilizing protocol for the $q$-ary $d$-dimensional de Bruijn graph ($q = \sqrt[d]{n}$) that is able to route any search request in at most $d$ hops w.h.p., while significantly lowering the node degree compared to the clique: We require nodes to have a degree of $\mathcal O(\sqrt[d]{n})$, which is asymptotically optimal for a fixed diameter $d$.The protocol keeps the expected amount of edge redirections per node in $\mathcal O(\sqrt[d]{n})$, when the number of nodes in the system increases by factor $2^d$.The number of messages that are periodically sent out by nodes is constant. AU - Feldmann, Michael AU - Scheideler, Christian ID - 125 SN - 978-3-319-69083-4 T2 - Proceedings of the 19th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS) TI - A Self-Stabilizing General De Bruijn Graph VL - 10616 ER - TY - CONF AB - We study the consensus problem in a synchronous distributed system of n nodes under an adaptive adversary that has a slightly outdated view of the system and can block all incoming and outgoing communication of a constant fraction of the nodes in each round. Motivated by a result of Ben-Or and Bar-Joseph (1998), showing that any consensus algorithm that is resilient against a linear number of crash faults requires $\tilde \Omega(\sqrt n)$ rounds in an n-node network against an adaptive adversary, we consider a late adaptive adversary, who has full knowledge of the network state at the beginning of the previous round and unlimited computational power, but is oblivious to the current state of the nodes. Our main contributions are randomized distributed algorithms that achieve consensus with high probability among all except a small constant fraction of the nodes (i.e., "almost-everywhere'') against a late adaptive adversary who can block up to ε n$ nodes in each round, for a small constant ε >0$. Our first protocol achieves binary almost-everywhere consensus and also guarantees a decision on the majority input value, thus ensuring plurality consensus. We also present an algorithm that achieves the same time complexity for multi-value consensus. Both of our algorithms succeed in $O(log n)$ rounds with high probability, thus showing an exponential gap to the $\tilde\Omega(\sqrt n)$ lower bound of Ben-Or and Bar-Joseph for strongly adaptive crash-failure adversaries, which can be strengthened to $\Omega(n)$ when allowing the adversary to block nodes instead of permanently crashing them. Our algorithms are scalable to large systems as each node contacts only an (amortized) constant number of peers in each communication round. We show that our algorithms are optimal up to constant (resp.\ sub-logarithmic) factors by proving that every almost-everywhere consensus protocol takes $\Omega(log_d n)$ rounds in the worst case, where d is an upper bound on the number of communication requests initiated per node in each round. We complement our theoretical results with an experimental evaluation of the binary almost-everywhere consensus protocol revealing a short convergence time even against an adversary blocking a large fraction of nodes. AU - Robinson, Peter AU - Scheideler, Christian AU - Setzer, Alexander ID - 3422 KW - distributed consensus KW - randomized algorithm KW - adaptive adversary KW - complexity lower bound SN - 978-1-4503-5799-9/18/07 T2 - Proceedings of the 30th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA) TI - Breaking the $\tilde\Omega(\sqrt{n})$ Barrier: Fast Consensus under a Late Adversary ER - TY - CONF AB - In this paper we present two major results: First, we introduce the first self-stabilizing version of a supervised overlay network (as introduced in~\cite{DBLP:conf/ispan/KothapalliS05}) by presenting a self-stabilizing supervised skip ring. Secondly, we show how to use the self-stabilizing supervised skip ring to construct an efficient self-stabilizing publish-subscribe system. That is, in addition to stabilizing the overlay network, every subscriber of a topic will eventually know all of the publications that have been issued so far for that topic. The communication work needed to processes a subscribe or unsubscribe operation is just a constant in a legitimate state, and the communication work of checking whether the system is still in a legitimate state is just a constant on expectation for the supervisor as well as any process in the system. AU - Feldmann, Michael AU - Kolb, Christina AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1163 KW - Topological Self-stabilization KW - Supervised Overlay KW - Publish-Subscribe System T2 - Proceedings of the 32nd IEEE International Parallel & Distributed Processing Symposium (IPDPS) TI - Self-Stabilizing Supervised Publish-Subscribe Systems ER - TY - CONF AB - We propose a distributed protocol for a queue, called Skueue, which spreads its data fairly onto multiple processes, avoiding bottlenecks in high throughput scenarios. Skueuecan be used in highly dynamic environments, through the addition of join and leave requests to the standard queue operations enqueue and dequeue. Furthermore Skueue satisfies sequential consistency in the asynchronous message passing model. Scalability is achieved by aggregating multiple requests to a batch, which can then be processed in a distributed fashion without hurting the queue semantics. Operations in Skueue need a logarithmic number of rounds w.h.p. until they are processed, even under a high rate of incoming requests. AU - Feldmann, Michael AU - Scheideler, Christian AU - Setzer, Alexander ID - 1164 T2 - Proceedings of the 32nd IEEE International Parallel & Distributed Processing Symposium (IPDPS) TI - Skueue: A Scalable and Sequentially Consistent Distributed Queue ER - TY - JOUR AU - J. Daymude, Joshua AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - Porter, Alexandra AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1796 IS - 1 JF - Natural Computing TI - On the runtime of universal coating for programmable matter ER - TY - CONF AU - Gmyr, Robert AU - Hinnenthal, Kristian AU - Kostitsyna, Irina AU - Kuhn, Fabian AU - Rudolph, Dorian AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 5764 T2 - Proceedings of the 24th International Conference on DNA Computing and Molecular Programming TI - Forming Tile Shapes with Simple Robots ER - TY - GEN AB - In this paper, we investigate the use of trusted execution environments (TEEs, such as Intel's SGX) for an anonymous communication infrastructure over untrusted networks. For this, we present the general idea of exploiting trusted execution environments for the purpose of anonymous communication, including a continuous-time security framework that models strong anonymity guarantees in the presence of an adversary that observes all network traffic and can adaptively corrupt a constant fraction of participating nodes. In our framework, a participating node can generate a number of unlinkable pseudonyms. Messages are sent from and to pseudonyms, allowing both senders and receivers of messages to remain anonymous. We introduce a concrete construction, which shows viability of our TEE-based approach to anonymous communication. The construction draws from techniques from cryptography and overlay networks. Our techniques are very general and can be used as a basis for future constructions with similar goals. AU - Blömer, Johannes AU - Bobolz, Jan AU - Scheideler, Christian AU - Setzer, Alexander ID - 5820 TI - Provably Anonymous Communication Based on Trusted Execution Environments ER -