P2P文件共享应用安全问题分析

介绍以P2P文件共享应用为例,分别从Peer用户安全、Peer的行为及共享文件三个方面讨论其安全问题,为P2P的安全技术研究工作提供比较全面的认识。     

Behavior-based reputation management in P2P file-sharing networks

Trust research has become a key issue in the last few years as a novel and valid solution to ensure the security and application in peer-to-peer (P2P) file-sharing networks. The accurate measure of trust and reputation is a hard problem, most of the existing trust mechanisms adopt the historical behavior feedback to compute trust and reputation. Thus exploring the appropriate transaction behavior becomes a fundamental challenge. In P2P system, each peer plays two roles: server and client with responsibility for providing resource service and trust recommending respectively. Considering the resource service behavior and trust recommending behavior of each peer, in this paper, we propose a new trust model adopting the technology to calculate eigenvectors of trust rating and recommending matrices. In our model, we define recommended reputation value to evaluate the resource service behavior, and recommending reputation value to evaluate the trust recommendation behavior. Our algorithm would make these two reputation values established an interrelated relation of reinforcing mutually. The normal peers provide authentic file uploading services, as well as give correct trust recommendation, so they can form a trusted and cooperative transaction community via the mutual reinforcement of recommended and recommending reputation values. In this way, the transaction behaviors of those malicious peers are isolated and confined effectively. Extensive experimental results also confirm the efficiency of our trust model against the threats of exaggeration, collusion, disguise, sybil and single-behavior.     

A D-S evidence theory based fuzzy trust model in file-sharing P2P networks

In this paper we propose an advanced Dempster-Shafer (D-S) Evidence Theory based Fuzzy Trust model (ETFT) for Peer-to-Peer (P2P) networks. The primary goal of ETFT is to be able to address trust information uncertainty and fuzzy trust inference to deal with inconsistent or conflicting recommendation problems in a reputation based P2P environment. The D-S theory is therefore introduced to our trust model. To make the D-S theory fit into P2P systems, we creatively revise the combination rules and achieve greatly improved results. To further improve the accuracy and performance, ETFT filters out noisy referrals before combining the evidences. From the theoretical analyses and experimental results, it is evident that the proposed ETFT has a clear advantage in modeling dynamic trust relationship and aggregating recommendation information. Results also demonstrate that ETFT is more robust and can generate higher successful transaction rate than most existing frameworks.     

An Eigentrust dynamic evolutionary model in P2P file-sharing systems

Many reputation systems have been proposed to distinguish malicious peers and to ensure the quality of the service in P2P file sharing systems. Most of those reputation systems implicitly assumed that normal peers are always altruistic and provide their resources unconditionally when requested. However, as independent decision makers in real networks, peers can be completely altruistic (always cooperative, ALLC), purely selfish (always defective, ALLD), or reciprocal (R). In addition, those systems do not provide an effective method to reduce free-riders in P2P networks. To address these two problems, in this paper, we propose an EigenTrust evolutionary game model based on the renowned EigenTrust reputation model. In our model, we use evolutionary game theory to model strategic peers and their transaction behaviors, which is close to the realistic scenario. Many experiments have been designed and performed to study the evolution of strategies and the emergence of cooperation under our proposed EigenTrust evolutionary model. The simulation results showed that rational users are inclined to cooperate (enthusiastically provide resources to other peers) even under some conditions in which malicious peers try to destroy the system.     

Evaluating stranger policies in P2P file-sharing systems with reciprocity mechanisms

How to deal with strangers efficiently is a big challenge for designing P2P systems, as ineffective stranger policies will cause the degradation of system performance and fairness. In this work, we focus on an open P2P file-sharing environment with reciprocity incentive mechanisms, and we evaluate the impact of different stranger policies to system performance and fairness using both numerical analyses and agent-based simulations. The results reveal that there exist tradeoffs between system performance and fairness; the optimal performance and fairness of the system cannot be reached simultaneously; free-riders will survive when system performance is optimal. The accuracy of this evaluation is verified through the analysis of stranger policies in BitTorrent and eMule/eDonkey. Therefore, this evaluation can effectively help P2P designers select appropriate stranger policies according to their individual design goals.     

A P2P streaming architecture supporting scalable media

Peer-to-peer (P2P) streaming solutions are changing the way real-time multimedia transmission is distributed over the Internet. The advances in video coding, like Scalable Video Coding, also turns possible high-quality/definition video distribution and consumption. The recent push in using the standard HTTP protocol for streaming videos in the World Wide Web, is also making converged entertainment services come closer to global deployment across TV, Tablet and mobile devices. The combination of Scalable Video, P2P networks and Web technologies for transmitting high-quality live and time-shifted media contents, is a potential area of innovation and a very actual research topic. This paper describes the architecture of a quality-centric P2P distribution network supporting adaptive and scalable streamable media, that decouples the transport mechanisms from the media content type and structure (video, audio, timed-data, timed-text), irrespective of their encoding schemes. The set of P2P streaming protocols designed for the network enables streaming of live and on-demand media, with very low signaling cost. Prototypes of the P2P network components were implemented and integrated in the streaming platform of EU FP7 SARACEN Project. A suite of tests for evaluation of the performance of the solution demonstrates that it keeps a fairly stable quality level with reduced amplitude and frequency of variations, raising the overall quality perceived by the end-user.     

User selfishness vs. file availability in P2P file-sharing systems: Evolutionary game theoretic approach

In a Peer-to-Peer (P2P) file-sharing system, a node finds and retrieves its desired file. If multiple nodes cache the same file to provide others, we can achieve a dependable file-sharing system with low latency and high file availability. However, a node has to spend costs, e.g., processing load or storage capacity, on caching a file. Consequently, a node may selfishly behave and hesitate to cache a file. In such a case, unpopular files are likely to disappear from the system. In this paper, we aim to reveal whether effective caching in the whole system emerges from autonomous and selfish node behavior. We discuss relationship between selfish node behavior and system dynamics by using evolutionary game theory. Through theoretic analysis, we show that a file-sharing system can be robust to file disappearance depending on a cost and demand model for caching even if nodes behave selfishly. Furthermore, we also conduct several simulation-based analysis in terms of network structures, evolving network, load balancing, and system stability. As a result, we demonstrate that a file-sharing system with good properties, i.e., robustness to file disappearance, low search latency, well load-balancing, and high stability, can be achieved independent of network structures and dynamics.     

Downloading trace study for BitTorrent P2P performance measurement and analysis

With the increasing client population and the explosive volume of Internet media content, the peer-to-peer networking technologies and systems provide a rapid and scalable content distribution mechanism in the global networks. The BitTorrent protocol and its derivatives are among the most popular peer-to-peer file sharing applications, which contribute a dominant fraction of today??s Internet traffic. In this paper, we conduct the performance measurement and analysis of BitTorrent systems with an extensive volume of real trace logs. We use several downloading-side metrics, including overall downloading time, maximum of downloading bandwidth, average bandwidth utilization, maximum of downloading connections, and average number of active connections, to derive various interesting results from the downloading-side aspect of network resource usage. Performance examination learns many new observations and characteristics into the virtue of BitTorrent protocols and systems, thereby providing beneficial information for bandwidth allocation and connection control in BitTorrent client applications. Therefore, this study is complementary to many previous research works that mainly focused on system-oriented and uploading-side performance measurements.     

A real-time responsiveness measurement method of linux-based mobile systems for P2P cloud systems

Linux-based mobile computing systems such as robots, electronic control devices, and smart-phone are the most important types of P2P cloud systems in recent days. To improve the overall performance of networked systems, each mobile computing system requires real-time characteristics. For this reason, mobile computing system developers want to know how well real-time responsiveness is supported; several real-time measurement tools have been proposed. However, those previous tools have their own measurement schemes and we think that the results from those models do not show how responsive those systems are. In this paper, we propose ELRM, a new real-time measurement method that has clear measurement interval definitions and an accurate measurement method for real-time responsiveness. We evaluate ELRM on various mobile computing systems and compare it with other existing models. As a result, our method can obtain more accurate and intuitive real-time responsiveness measurement results.     

BitTorrent-like P2P approaches for VoD: A comparative study

The enormous popularity of Video on Demand (VoD) has attracted substantial research attention into the effective use of peer-to-peer (P2P) architectures to provide solutions at large-scale. In particular, the high efficiency of BitTorrent has inspired many P2P protocols for VoD. However, these protocols use different approaches to adapt the design of Bittorrent to VoD, and in most cases their performance has been evaluated separately and in limited scenarios. As a consequence, the research community still lacks a clear understanding of how these protocols compare against each other and how well each of them would work in real world conditions, where, for instance, peers have heterogeneous bandwidths, may freeride or may be located behind NAT/firewall.In this paper, we propose a simulation based methodology which aims at putting forward a common base for comparing the performance of these different protocols under a wide range of conditions. We show that, despite their considerable differences: (i) existing BitTorrent-like VoD approaches all share some characteristics, such as that their bandwidth reciprocity based methods to incentivize cooperation do not always yield an optimal overall performance. Furthermore, we demonstrate that (ii) in these protocols there is a trade-off between QoS and resilience to freeriding and malicious attacks. We also discover that, (iii) when peers doing streaming coexist with peers doing traditional file transfer, the latter actually benefit from this coexistence, at the expenses of the former. Finally, we show that (iv) early departures of peers from the system do not significantly affect the QoS delivered, while jumping to a different position in the file has a bigger negative impact. Overall, our findings provide important implications for both VoD service providers and future system designers. On the one hand, our results can guide VoD service providers in selecting the most appropriate protocol for a given environment. On the other hand, exposing the flaws of current approaches will help researchers in improving them and/or designing better ones.     

Diverse community: Demand differentiation in P2P live streaming

Peer-to-Peer (P2P) technology has become an attractive approach for enabling large-scale video streaming applications, but the factor of users’ subjective preferences is not paid enough attention in such networks. As users have various demand on video qualities, we can provide them with video streams at different resolutions without impairing their satisfaction. The adaptive streaming rate technique is a promising method. However, in providing adaptive streaming rate services, P2P live streaming design faces the following challenge: how to provide all users with uninterrupted video with their desired qualities in case that their demand dynamically changes? To shed more light on this problem, we first derive a model and formulate the problem as a resource demand vs supply problem. Then we present a framework to address the challenge via efficient bandwidth allocation and group cooperation. Through comprehensive simulations, we evaluate the effectiveness of the proposed framework, and conclude that it effectively helps existing solutions, such as Partial Participation Scheme (PPS), achieve better performance.     

基于多重属性的P2P网络节点重要性度量方法

P2 P网络中的节点重要性评价在实际应用中有重要意义。现有的一些重要性评价指标如度、紧密度等存在度量结果较为片面等缺点,单一指标并不能有效地对P2 P网络中的节点重要性进行度量。针对此问题,提出了一种基于多重属性的综合度量指标。以节点度作为对比基础,计算多个度量指标与节点度指标的肯德尔相关系数,通过分析多个指标之间的内在关联性,最终选择节点度、介数、K-核和PageRank四个属性来进行节点重要性的综合度量。通过真实的P2 P网络进行实验验证,结果表明,相对原有单一度量指标和现有的综合度量指标,该综合指标更能够有效地对P2 P网络中的节点重要性进行度量,而且具有较强的普适性,可以应用到大多数P2 P网络中。     

A modula-2 kernel for supporting monitors

The concept of the monitor as a device for handling the problems of mutual exclusion and synchronization in a set of concurrent processes is now well understood. In addition to being of considerable theoretical interest, the monitor concept has been found suitable for the design of several practical operating systems. This paper discusses an implementation of monitors using a kernel written in Modula-2.     

Measurement study on P2P streaming systems

Originally used as the default infrastructure for efficient file sharing, peer-to-peer (P2P) architecture achieved great successes. Now, the P2P model has been adopted for many other distributed applications, such as instant message and phone services, Internet gaming, and large-scale scientific computing. In recent years, P2P streaming systems experienced tremendous growth and became one of the largest bandwidth consumers on the Internet. Compared to standard file sharing systems, the streaming services show unique characteristics with more stringent time constraints and require much higher network bandwidth. It is extremely important to evaluate and analyze existing applications, and investigate the merits and weaknesses in these systems for future development. In this paper, we conduct a comprehensive measurement study on two of the most popular P2P streaming systems, namely, PPLive and PPStream. They are very popular P2P streaming applications, and serving millions of registered users with hundreds of live TV channels and millions of other video clips. In our measurement, we deploy our collectors in China, and both live TV and video-on-demand (VoD) channels are evaluated. We record run-time network traffic on the client side, compare and analyze the characteristics of these channels based on their popularity. For both categories, we perceive that, in general, the two measured P2P streaming systems provide satisfactory experience to the audiences for all channels regardless of popularity. However, the most of data are downloaded from the dedicated servers for unpopular channels. We also observe that live TV channels show better peer coordination than VoD channels. Beside the traffic, we have also collected cache replacement information for VoD channels, and these measurement results can help us understand the caching mechanism of P2P streaming systems. With the support of the cache, VoD channels perform better than their counterparts in the live TV category in terms of data transmission, workload distribution, and signal traffic overhead. Overall, our results reveal that although P2P streaming systems can usually provide excellent viewing experience for popular channels, there are still challenges to fully support unpopular channels. New designs and algorithms are in urgent need, especially for unpopular live TV channels.     

一种通用的P2P模拟器

点对点（Peer-to-Peer）算法已成为一项热门研究。但作为验证其有效性的工具——P2P模拟器却没有受到过多的关注。现存的P2P模拟器存在很多问题,如可扩展性差、通用性差、模拟节点的数量小、忽略底层网络等。为解决这些问题,提出一种通用P2P模拟器。介绍了该模拟器的系统架构和设计实现,并通过一个实验展现其使用状况。实验证明,该模拟器是有效的,可适用于大规模P2P模拟。     

一种通用的P2P模拟器

点对点(Peer-to-peer)算法已成为一项热门研究.但作为验证其有效性的工具--P2P模拟器却没有受到过多的关注.现存的P2P模拟器存在很多问题,如可扩展性差、通用性差、模拟节点的数量小、忽略底层网络等.为解决这些问题,提出一种通用P2P模拟器.介绍了该模拟器的系统架构和设计实现,并通过一个实验展现其使用状况.实验证明,该模拟器是有效的,可适用于大规模P2P模拟.     

一种基于信任P2P模型

提出一种基于全局信任度的分布式P2P信任模型,给出了求解信任度的数学模型和具体求解方法.通过冗余备份的方式份提高信任值保存的可靠性.基于次模型进行仿真实验,通过实验结果的分析,验证此模型能够有效隔离恶意节点,提高P2P系统的交易成功率.     

一种分组P2P网络模型

Internet的飞速发展使对等网络(P2P)及其相关领域的研究成为热点,但是当前P2P网络的结构并不完善。文中介绍了几种P2P模型,并在综合这几种模型优点的基础上,针对P2P网络的动态特性提出了一种分组P2P模型。该模型使用组节点管理对等点的加入和退出,有助于提高对等网络的稳定性。