Anonymity analysis of P2P anonymous communication systems

Compared with traditional static Client/Server architecture, the P2P architecture is more suitable for anonymous communication systems because it is more flexible and can keep load balance better. However, in order to make the system usable and reliable, some system designs make tradeoffs between anonymity and performance such as reliability, latency and throughput. Tradeoffs are sometimes unavoidable in system design, but which tradeoffs are acceptable and which are not is very important for developers. This paper models the P2P anonymous communications and takes quantitative analysis of anonymity by information theory with entropy. Based on this analysis, it studies the effect of key system design strategies on anonymity in network architecture, routing and message relay, and measures which strategies should be used in anonymous communications and which are unreasonable. Some analysis results are contrary to our intuition. For example, it quantitatively concludes that in some cases the anonymity is not enhanced when the system scale increases, and too long an anonymous tunnel may not provide higher anonymity but lowers performance. These analysis results are valuable for developers of P2P anonymous communication systems. Besides, this paper also discusses some possible strategies such as trust and reputation to enhance the P2P anonymous communications.     

P Systems with Mobile Membranes

P systems with active membranes are among the central ones in membrane computing, and they were shown to be both computationally universal (able to simulate Turing machines) and computationally efficient (able to solve hard problems in polynomial time). However, in all cases, these results were obtained by making use of several powerful features, such as membrane polarization, label changing, division of non-elementary membranes, priorities, or cooperative rules. This paper contributes to the research effort of introducing a class of P systems with active membranes having none of the features mentioned above, but still preserving the power and the efficiency. The additional feature we consider instead are the operations of endocytosis and exocytosis: moving a membrane inside a neighboring membrane, or outside the membrane where it is placed. We investigate the power and the efficiency of these systems (also using membrane division) by first proving that they can simulate (with a linear slowdown and without introducing non-determinism) rewriting P systems with 2-replication, for which the universality and the possibility of solving NP-complete problems in polynomial time are known. In this way, the universality and efficiency are also obtained for our systems. We also give a direct and simple proof for the universality result – without using division rules (the proof uses nine membranes, but we do not know whether this number can be decreased).     

Translating Mobile Ambients into P Systems

We present a translation of the mobile ambients without communication and replication into P systems with mobile membranes. We introduce a set of developmental rules over membranes, and describe the correspondence between the behaviour of an ambient and the evolution of its translated membrane system. We give an operational correspondence result between the mobile ambients and P systems.     

Degree-Optimal Routing for P2P Systems

We define a family of Distributed Hash Table systems whose aim is to combine the routing efficiency of randomized networks—e.g. optimal average path length O(log ² n/δlog δ) with δ degree—with the programmability and startup efficiency of a uniform overlay—that is, a deterministic system in which the overlay network is transitive and greedy routing is optimal. It is known that Ω(log n) is a lower bound on the average path length for uniform overlays with O(log n) degree (Xu et al., IEEE J. Sel. Areas Commun. 22(1), 151–163, 2004). Our work is inspired by neighbor-of-neighbor (NoN) routing, a recently introduced variation of greedy routing that allows us to achieve optimal average path length in randomized networks. The advantage of our proposal is that of allowing the NoN technique to be implemented without adding any overhead to the corresponding deterministic network. We propose a family of networks parameterized with a positive integer c which measures the amount of randomness that is used. By varying the value c, the system goes from the deterministic case (c=1) to an “almost uniform” system. Increasing c to relatively low values allows for routing with asymptotically optimal average path length while retaining most of the advantages of a uniform system, such as easy programmability and quick bootstrap of the nodes entering the system. We also provide a matching lower bound for the average path length of the routing schemes for any c. This work was partially supported by the Italian FIRB project “WEB-MINDS” (Wide-scalE, Broadband MIddleware for Network Distributed Services), .     

一种基于分区的移动P2P网络路由算法

校园内无线网络的普遍使用与移动设备性能的快速发展,使移动P2P技术得到了更多的关注。但当前对移动对等网络的研究还缺乏统一而明确的定义,还存在很多未能很好地解决的问题。文中的研究目的是如何有效组织移动节点,进行资源交换。针对校园无线网络环境,提出了一种基于分区模型的移动P2P网络结构。对节点历史行为统计,计算节点性能值。并利用分区网络模型和机会路由的思想提出了一种改进路由算法,实现区域内和区域间路由转发,降低了路由开销,提高了网络性能。     

基于移动代理的结构化P2P网络模型

为了符合实际P2P网络中的节点异质性的情形并支持语义查询,在分析自组织网络模型和双层结构化P2P网络模型以后,提出了一种基于移动代理的结构化P2P网络模型AS-P2P.理论分析和模拟实验结果表明,在加入了移动代理转移资源索引和使用双层结构化P2P网络区别节点能力以后,AS-P2P更加适应动态网络,并具有平均查找长度短,超级节点上负载均衡和资源索引分类等优点.     

一种P2P系统中自适应的动态信任度量

P2P系统中信任评估一个重要的挑战是如何有效处理恶意节点的策略性行为改变.现有的信任度量对信任关系的动态性的支持不足,影响了信任评估的准确性和动态适应能力.为此,提出一个自适应的动态信任度量,该模型充分考虑经验和时间因素对信任动态性的影响,引入了自适应遗忘因子和累积滥用信任两个参数来更新节点信任度,并通过反馈控制机制动态调节上述参数,提高了信任模型的动态适应能力.仿真实验表明,和已有的信任模型相比,提出的动态信任度量具有更好的动态适应能力,能够有效处理动态恶意节点策略性的行为改变对系统的攻击.     

Stochastic Optimization for Content Sharing in P2P Systems

Available resources in peer-to-peer (P2P) systems depend strongly on resource contributions made by individual peers. Empirical data shows that in the absence of incentives, a majority of the participating peers do not contribute resources. Modeling interactions between individual peers is often difficult as the number of peers in the system can be very large, and the relationships among them can be very complex. In this paper, we propose a new solution for P2P systems, where peers upload and download content to and from the contributing peers based on agreed-upon/determined sharing rates. We propose a P2P solution that deters free-riders by imposing constraints on participating peers; specifically, a peer is allowed access to new content only as long as its own content contribution exceeds an adaptively set threshold. The constraints are enforced either by a central authority (e.g., a tracker) or by a decentralized coalition of peers in a swarm, social network, etc. We derive optimal upload policies for the peers given their estimated future download requirements and their previous contribution (credit) to the other peers. Our results show considerable improvement in the cost-benefit tradeoff for peers that deploy such an optimal policy as compared to heuristic upload policies. We also propose mechanisms based on which the coalition of peers can provide incentives or penalties to participating peers to adjust their policies such that the availability of content and/or number of peers contributing content is maximized.     

P2P系统的存储和索引框架

该文介绍一个模块化的存储和索引框架,它清晰地划分P2P系统的功能部件,能按照不同Internet应用的特定需要编制P2P的基础结构。     

基于增强稳定组模型的移动P2P网络信任评估方法

目前,己经有许多文献给出了移动P2P网络环境下信任管理技术与具体应用的集成方案.现存的信任模型都存在一个共同的假设,即假设信任信息都来自于稳定的网络拓扑结构环境下,且这些信任信息能够被保证长期有效.然而移动P2P网络由于节点频繁的加入和退出造成网络拓扑结构不断变化,不可能保证建立的信任信息长期有效.因此,已有的信任管理系统在这种移动环境下已经不再适用,迫切需要提出新的解决方案.通过研究移动P2P节点的信任关系的变化与网络使用者的兴趣、爱好等变化的对应关系,该文提出了一个基于增强的稳定组模型(Enhanced Stable Group Model-based Trust Evaluation Method,SGTM)的信任评估方法,并给出了稳定组构造算法.该机制利用稳定组构造算法对移动P2P网络进行有效地分组,相同分组内的节点之间相对保持最大程度的拓扑结构的稳定,从而保证组内节点信任关系的稳定存在.文中在移动环境下对移动模式和信任管理之间的关系问题进行了详细的研究.模拟实验从动态适应力、全局信誉的收敛时间以及全局信任计算所涉及的通讯负载等方面对所提出的信任评估方法的性能进行了评估.     

移动通信中双向认证和密钥协商协议

移动通信增值服务的关键技术之一就是设计既满足较差计算性能又具有良好安全性的协议。文章在Lowe改进的BANconcreteAndrewSecureRPC协议的基础上引入带密钥的哈希函数,生成一个新的移动通信认证和密钥协商协议Advanced-RPC。该协议规避了原协议存在的密钥泄漏风险,增加了向前安全性,同时提高了执行效率;与其它同类协议相比,也具有明显的高效性和简洁性。     

移动环境中一种基于Hash的P2P覆盖网

目前提出的大多数基于哈希（hash—based）的P2P网络都集中于固定的对等节点。当节点移动到网络中一个新的位置时,这种结构在消息传递等方面的效率就会下降。文章提出一种移动环境中的基于哈希的P2P覆盖网（Hash—based P2P Overlay in Mobile Environment,H—MP2P）,允许节点在网络中自由移动。一个节点可通过P2P网络广播其位置信息,其他节点通过网络可以获知该节点的移动信息并进行定位。通过理论分析和实验可知H—MP2P在扩展性、可靠性和效率方面都可以取得较好的结果,可以很好的应用在移动环境中。     

构造移动P2P环境下的分布式信任模型

基于固定网络的信任模型缺乏对网络高度动态性的考虑,不能直接应用于移动P2P网络。本文利用节点的报文转发能力,提出了一种移动P2P环境下的分布式信任模型MobTrust。该模型通过分布式存储机制,将节点转发的评价数据备份于K桶中,扩充了评价数据的存储范围。同时,鉴于移动设备有限的计算能力,设计双反馈机制提高评价数据的可靠性,然后以轻量级的方式计算信任度。仿真结果表明,MobTrust能有效降低系统开销,并拥有较高的评价数据利用率和交易成功率。     

移动P2P社会网络中关键节点发现方法

传统的消息传播关键节点发现方法大多针对静态网络进行研究。针对移动P2P社会网络这类复杂的动态时变网络,提出了一种其时效性随时间和传播路径衰减的一般类型消息传播过程中关键节点的发现方法。将静态网络中基于通路(walk)的节点中心性分析方法扩展到移动P2P社会网络中,将消息传播路径分解到时间一空间两个维度上,并利用两个衰减因子分别刻画消息的效用随传播路径长度衰减及随时间推移衰减这两种自然特性,利用节点的历史相遇信息,得到了节点传播能力的量化分析函数,以此刻画节点对时效性消息的相对传播能力。基于真实Trace数据的实验结果验证了该方法的可行性。由于所述方法考虑了消息时空两个维度上所有可能的传播路径,也可用于有效预测网络的演化和不同节点在未来传播或获取消息时的相对重要程度。     

一种采用瘦服务器的P2P网络关键字搜索算法

P2P技术是未来网络中的关键技术,而搜索算法是决定对等同系统性能的首要因素,本文吸收了现有P2P搜索算法各自的优点,提出了基于瘦服务器的关键字搜索算法,将服务器从巨大的搜索请求响应负担中解脱出来,仅负责搜索树的创立和维护,将搜索任务分散到网络各个节点上去,在充分利用各个节点自身的能力的基础上,又保留了整个网络结构的信息,因此具有结构化对等网系统搜索算法高查全率、低冗余消息以及可扩展性好的优点,也同时保有了非结构化对等网节点平等,结构灵活,维护简单的优势     

DiCAS: An Efficient Distributed Caching Mechanism for P2P Systems

Peer-to-peer networks are widely criticized for their inefficient flooding search mechanism. Distributed Hash Table (DHT) algorithms have been proposed to improve the search efficiency by mapping the index of a file to a unique peer based on predefined hash functions. However, the tight coupling between indices and hosting peers incurs high maintenance cost in a highly dynamic network. To properly balance the tradeoff between the costs of indexing and searching, we propose the distributed caching and adaptive search (DiCAS) algorithm, where indices are passively cached in a group of peers based on a predefined hash function. Guided by the same function, adaptive search selectively forwards queries to "matched” peers with a high probability of caching the desired indices. The search cost is reduced due to shrunk searching space. Different from the DHT solutions, distributed caching loosely maps the index of a file to a group of peers in a passive fashion, which saves the cost of updating indices. Our simulation study shows that the DiCAS protocol can significantly reduce the network search traffic with the help of small cache space contributed by each individual peer.     

PATCOM:基于分割树的无结构P2P系统一致性维护方法

无结构P2P技术逐渐被应用在新型的协同计算系统中.这些新型业务支持数据的动态更新,不仅要求副本数据的强一致性,而且要求更新数据的快速传播.高效的一致性维护方法是保证新业务顺利开展的基础.在比较分析现有的P2P系统一致性维护方法的基础上,针对无结构P2P系统,提出了一种基于分割树的一致性维护方法--PATCOM.PATCOM使用Chord协议作为组管理协议,通过不断分割由副本节点组成的Chord环,动态地建立更新消息传播树(Update Message Propagation Tree,UMPT).论文进一步从理论上分析了UMPT的平均高度、PATCOM的性能、容错能力以及算法开销,并和基于Gossip的一致性维护方法进行了比较.理论分析和仿真实验结果表明:PATCOM不仅能够快速地维护P2P系统的强一致性,而且产生的冗余更新消息少.     

Self-Management Framework for Mobile Autonomous Systems

The advent of mobile and ubiquitous systems has enabled the development of autonomous systems such as wireless-sensors for environmental data collection and teams of collaborating Unmanned Autonomous Vehicles (UAVs) used in missions unsuitable for humans. However, with these range of new application-domains comes a new challenge—enabling self-management in mobile autonomous systems. Autonomous systems have to be able to manage themselves individually as well as form self-managing teams which are able to adapt to failures, protect themselves from attacks and optimise performance. This paper proposes a novel distributed policy-based framework that enables autonomous systems of varying scale to perform self-management individually and as a team. The framework allows missions to be specified in terms of roles in an adaptable and reusable way, enables dynamic and secure team formation with a utility-based approach for optimal role assignment, caters for communication link maintenance amongst team-members and recovery from failure. Adaptive management is achieved by employing a policy-based architecture to enable dynamic modification of the management strategy relating to resources, role behaviour, communications and team management, without interrupting the basic software within the system. Evaluation of the framework shows that it is scalable with respect to the number of roles, and consequently the number of autonomous systems involved in the mission. It is also optimal with respect to role assignments, and robust to intermittent communication link and permanent team-member failures.     

结构化P2P系统路由机制的研究

基于分布式哈希表的结构化P2P系统得到了广泛的研究,这些系统的网络拓扑结构一般都以图论中的一些广为研究的图作基础,而且大量借鉴了并行系统的研究成果。介绍了几个常见的结构化P2P系统,对其拓扑结构和路由算法作了分析对比。