Proposition de stage Labex SMART
Titre : Tractable Reliable Communication in Dynamic Compromised Networks Encadrant : Sébastien Tixeuil, Professeur UPMC
Laboratoire d’accueil : LIP6
Axe thématique : la mobilité dans les réseaux et l’interopérabilité
Sujet du stage :Recent years proved the opportunistic use of available networks extremely useful to offload trafic in a cost efficient manner while preserving quality of service. Such networks are typically highly dynamic as their participants move and opportunistically reconnect as new neighbors are discovered. However, exchanging information across multiple hops in such (uncontrolled) networks poses a serious security challenge: potential attackers are now insiders.
In a recent paper [1], Maurer et al. considered the following problem: two nodes want to reliably communicate in a dynamic multi-hop network where a subset of the nodes have been compromised (and may have a totally arbitrary and unpredictable behavior, that is, they are Byzantine). They focused on cryptography-free solutions, as the network compromission could imply that the cryptographic infrastructure itself is compromised. In static networks, a necessary and sufficient condition for reliable multi-hop communication with k Byzantine nodes is the existence of 2k+1 disjoint paths between the source and the destination. However, this result is based on Menger's theorem (that relates the minimal node cut to network connectivity), which becomes incorrect in the case of dynamic networks. Maurer et al. proved a necessary and sufficient condition (in other words, the weakest possible condition) for enabling reliable communication in a dynamic multi-hop network where a subset of the nodes are Byzantine. Their proof is constructive, as they provide a Byzantine-resilient algorithm for reliable communication that is optimal with respect to their impossibility result.
Although the condition provided by Maurer et al. is the best possible from a theoretical point of view, it lacks practicality. That is, verifying their condition locally at every node requires to run at each node upon every message reception an exponential time algorithm. The first goal of the internship is to devise weaker conditions (that is, conditions that are sufficient, but not necessary) that can be computed locally in polynomial time. The efficiency of the new condition will be assessed through real traces of dynamic networks (e.g. body area networks, vehicular networks evolving in a real city, opportunistic networks, etc.). The second goal of the internship is to evaluate the effectiveness of cryptographic tools availability in this context, that is, the tradeoff between sufficient condition weakening and added communication overhead.
Bibliographie :
[1] Reliable Communication in a Dynamic Network in the Presence of Byzantine Faults. Best Paper Award. Alexandre Maurer, Xavier Défago, and Sébastien Tixeuil. In Proceedings of the IEEE International Symposium on Reliable Distributed Systems (SRDS 2015), Montréal, Canada, September 2015.
Durée du stage : 5 ou 6 mois
Compétences espérées : Algorithmique distribuée, Probabilités, Programmation en Python.
