Measurement and vulnerability analysis of overlay networks and peer-to-peer systems (2012)

Overlay networks and peer-to-peer systems typically encompass a large portion of the Internet with numerous entities in the systems that get coupled together to form a huge network. Some of these have successfully managed to be the killer network applications in the Internet over years. For example, the BitTorrent file sharing network traffic was estimated to cover 30% of Internet's traffic in 2004. Given the knowledge that such networks have a very large foot print on the Internet, it is crucial to understand the characteristics of such networks, for example, in terms of their usage statistics; the kind of content they make available. Furthermore, although the peer-to-peer paradigm can provide reduced cost and rapid deployment, it also generates a vast array of new security concerns. The loss of control from a central infrastructure leads to a wide range of new vulnerabilities that can be exploited by attackers. Therefore, it is very important to understand if one or more entities in a given peer-to-peer network can be compromised to launch attacks against entities inside or outside the peer-to-peer network. One way to understand such networks is to perform detailed measurement studies of, ideally, all or some of the entities involved. Measuring various aspects of such systems not only helps understand their current scale and impact on the Internet, but also uncovers any design or implementation deficiencies in the system aiding in the performance improvement of the overall system. 
In this dissertation, we use Internet measurement as the primary methodology to understand and evaluate various peer-to-peer networks and overlay systems. First, we perform extensive measurement studies on three popular overlay systems BitTorrent, Tor, and Xunlei. BitTorrent is the most successful open Internet application for content distribution. We seek to provide a nearly complete picture of the entire public BitTorrent Ecosystem. To this end, we develop a high-performance measurement infrastructure to study in-depth the Ecosystems torrent-discovery, tracker, peer, user behavior, and content landscapes. We also undertake a comprehensive measurement study of the private BitTorrent ecosystem called BitTorrent darknets. We examine BitTorrent darknets from macroscopic, medium-scopic and microscopic perspectives; estimate the size of the darknet world, compare the statistics of the private world with those of the public world, and analyze the effectiveness of policies provided by private sites in incentivizing users to seed files longer. The public and private BitTorrent studies provide a vivid picture of the entire BitTorrent ecosystem today. We also measure and analyze Xunlei, a peer-assisted file download acceleration system that is enormously popular in China. By performing an extensive protocol analysis on Xunlei, we develop a comprehensive measurement infrastructure, enabling us to gain new insights into the scale of Xunlei's content indexing, swarm size scales, and several unique characteristics of Xunlei's operation. 
We then study Tor, the most widely used anonymity network in the Internet. Via extensive measurements, we provide a thorough understanding of delays in Tor and identify the key entities in the system that contribute to the majority of delays perceived. Our findings should facilitate the analysis of solution space for reducing Tor delays. 
Having understood the scale and impact of these overlay systems, we next examine two peer-to-peer systems—a peer-to-peer file sharing system (BitTorrent) and a peer-to-peer live video streaming system (PPLive) for their resilience to different kinds of attacks. We find that BitTorrent is inherently resilient to attacks against two of its most important entities—leechers and seeds. However, we observe that the attack that we discover against peer-to-peer live video streaming systems can drive away more than 85% of the viewers of a given video channel. We believe that the results presented in this dissertation will be useful to distributed systems researchers in improving the designs of existing systems as well as designing robust and secure systems in the future.