How many eyes are spying on your shared folders?

Today peer-to-peer (P2P) file sharing networks help tens of millions of users to share contents on the Internet. However, users' private files in their shared folders might become accessible to everybody inadvertently. In this paper, we investigate this kind of user privacy exposures in Kad, one of the biggest P2P file sharing networks, and try to answer two questions: Q1. Whether and to what extent does this problem exist in current systems? Q2. Are attackers aware of this privacy vulnerability and are they abusing obtained private information? We build a monitoring system called Dragonfly based on the eclipse mechanism to passively monitor sharing and downloading events in Kad. We also use the Honeyfile approach to share forged private information to observe attackers' behaviors. Based on Dragonfly and Honeyfiles, we give affirmative answers to the above two questions. Within two weeks, more than five thousand private files related to ten sensitive keywords were shared by Kad users, and over half of them come from Italy and Spain. Within one month, each honey file was downloaded for about 40 times in average, and its inner password information was exploited for 25 times. These results show that this privacy problem has become a serious threat for P2P users. Finally, we design and implement Numen, a plug-in for eMule, which can effectively protect user private files from being shared without notice. Copyright 2012 ACM.EI

A collaborative P2P Scheme for NAT Traversal Server discovery based on topological information

In the current Internet picture more than 70% of the hosts are located behind Network Address Translators (NATs). This is not a problem for the client/server paradigm. However, the Internet has evolved, and nowadays the largest portion of the traffic is due to peer-to-peer (p2p) applications. This scenario presents an important challenge: two hosts behind NATs (NATed hosts) cannot establish direct communications. The easiest way to solve this problem is by using a third entity, called Relay, that forwards the traffic between the NATed hosts. Although many efforts have been devoted to avoid the use of Relays, they are still needed in many situations. Hence, the selection of a suitable Relay becomes critical to many p2p applications. In this paper, we propose the Gradual Proximity Algorithm (GPA): a simple algorithm that guarantees the selection of a topologically close-by Relay. We present a measurement-based analysis, showing that the GPA minimizes both the delay of the relayed communication and the transit traffic generated by the Relay, being a QoS-aware and ISP-friendly solution. Furthermore, the paper presents the Peer-to-Peer NAT Traversal Architecture (P2P-NTA), which is a global, distributed and collaborative solution, based on the GPA. This architecture addresses the Relay discovery/selection problem. We have performed large-scale simulations based on real measurements, which validate our proposal. The results demonstrate that the P2P-NTA performs similarly to direct communications with reasonably large deployments of p2p applications. In fact, only 5% of the communications experience an extra delay that may degrade the QoS due to the use of Relays. Furthermore, the amount of extra transit traffic generated is only 6%. We also show that the P2P-NTA largely outperforms other proposals, where the QoS degradation affects up to more than 50% of the communications, and the extra traffic generated goes beyond 80%.This work has been partially funded by the Grants MEDIANET (S2009/TIC-1466) from the Regional Government of Madrid and CON-PARTE (TEC2007-67966-C03- 03) by the Ministry of Science and Innovation of Spain.Publicad

On exceptional stress assignment in Latvian: the case of prefixes

This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Baltic Studies on 09.05.2018, available at: https://doi.org/10.1080/01629778.2018.1466817.In this article, we examine some previously understudied exceptions to the generalization that Latvian assigns stress to the left-most syllable in a prosodic word, specifically those that involve prefixation. We will show that these apparent exceptions in stress assignment follow from the internal structural properties of the word and are a result of attaching the prefix outside the domain where stress is assigned, which is up to the first functional head inside the hierarchy. Our treatment combines the syntactic structure of a neoconstructionist approach to word formation with an optimality theory formalization at the phonological level