Structures et algorithmes pour la coopération pair à pair

Peer-to-peer overlay networks are distributed systems, without any hierarchical organization or centralized control. Peers form overlay networks that are on top of the Internet. Both parts of this thesis deal with peer-to-peer overlay networks. The first part builds an unstructured one to construct a large scale Networked Virtual Environment. We present a complete study of a Delaunay-based overlay for massively shared virtual worlds. We design an overlay network matching the Delaunay triangulation of the participating peers. Especially, we describe the self-organizing algorithms for peer insertion and deletion. To reduce the delay penalty of overlay routing, we propose to augment each node with a limited number of carefully selected shortcut links creating a small-world. We show that a small number of shortcuts is sufficient to significantly decrease the delay of routing. The second part of this thesis gives insights on how the users of a real life structured peer-to-peer network behave. We give a detailed background on KAD, a Distributed Hash Table based on Kademlia, a file sharing system with several million simultaneous users. We describe the organization of the peers, and the search and the publish operations. We have been crawling KAD continuously for more than a year. We obtained information about geographical distribution of peers, session times, peer availability, and peer lifetime. As we have been studying KAD we have been both, fascinated and frightened by the possibilities KAD offers. Mounting a Sybil attack is very easy and allows to compromise the privacy of users, to compromise the correct operation of the key lookup and to mount a DDOS attack.PARIS-Télécom ParisTech (751132302) / SudocSudocFranceF