2015, Vol.*No.*, *-*Article ID DOI Title：字体Arial Black，字号小一 Author 如：PENG *Arial 加粗 五号姓前名后，姓全部大写，名首字母大写1, LU *1,2有一个单位以上，在作者名后加上标1,2,若学生为第一作者，导师为通讯作者，则导师名字后加, （姓前名后，姓全部大写，名首字母大写）1. Ele作者单位具体到二级单位，给出城市，times new roman 小五号 首行缩进2字符ctronic Engineering Department, Shanghai Jiao Tong University, Shanghai 200240, China;2. School of Information Security Engineering, Shanghai Jiao Tong University, Shanghai 200240, China WuhaTimes new roman 六号字n University and Springer-Verlag Berlin Heidelberg 2011Abstract:Arial 小五 加粗 In P2P (Peer-to-Peer) networks, some malicious peers can impact overall networks performance. One of the malicious behaviors of these peers is malicious packet dropping. In this paper, our focus is to detect and to exclude peers that misbehave by dropping some or all packets. Here, we propose a reputation-based mechanism for solving the problem efficiently. The proposedTimes new roman 小五 mechanism uses both direct reputation information and indirect reputation information to compute comprehensive reputation of a peer. At the same time, history reputation information is also taken into account when providing in faults tolerance capability and we regulate the imprecision based on the fact that the cause of packet dropping can be complex. Finally, the peers with bad comprehensive reputation can be detected easily and then will be excluded from the network. In this way, our proposed mechanism improves the performance of P2P networks without increasing computational overhead.Key words: P2P (Peer-to-Peer); reputation; malicious peers; packet dropping（关键词以分号隔开）CLC number: TP 305Received dateArial 六号 加粗: 2011-06-23Times new roman 六号Foundation item: Supported by the National Key Basic Research Program of China(973 Program) (2010CB731403) and the Opening Project of Key Lab of Information Network Security of Ministry of Public Security (C09607).（注意基金格式） Biography: PENG Hao, male, Ph.D. candidate, research direction: network communications and information security. E-mail: penghao2007 sjtu.edu.cn 作者名后若有，则脚注也应该有，前后呼应To whom correspondence should be addressed. E-mail: snlusjtu.edu.cn0 Introduction一级标题从0开始，实词首字母大写，Arial 加粗，四号 （标题每个实词首字母大写）正文内容：字体Times New Romans，字号五号。公式字号用10.5磅Peer-to-Peer (P2P)（正文中第一次出现缩写要先写全称后缩写，后文出现用缩写，专有名词首字母大写） networking has become a very active research area in recent years because of its advantages over the traditional Client/Server model for applications like file sharing, distributed computing, collaborative applications, etc. However, the open nature of P2P networks makes them vulnerable for malicious peers trying to manipulate the network.To solve this problem, many researchers have proposed various methods based on the reputation model and achieved degrees of success. There are mainly three kinds of reputation models: web-based, policy- based, and reputation-based reputation model 1,2（参考文献上标，并需在文中按数字顺序出现）. These models can be directly or indirectly introduced into P2P networks to build reputation between peers. However, while peers identity privacy is important, it is difficult to be achieved in fully distributed P2P networks, because reputation usually depends on information related to identity.Previous works have focused on developing various reputation models and enhancing identity privacy for P2P networks in a number of ways. Ref. 3（当以Ref.*类型出现时不上标） discusses the conflicts between privacy and reputation and proposes a trade-off model between them. In this model, it introduces multi-pseudonym to protect peers identity privacy. Although all the pseudonyms of a peer may not be linked together by attackers, privacy is not well protected because each pseudonyms transaction can still be linked. Ref. 4 alleviates the identity privacy problem in reputation negotiation by hiding the peers credentials. However, the negotiation process also depends on the disclosure of information related to each peers identity. Ref. 5 proposes a reputation-based P2P network to achieve peers anonymity by changing the pseudonym. However, it is implemented using an online Trusted Third Part (TTP).It is acknowledged that identity privacy in fully distributed P2P networks is desirable and necessary, but hard to achieve when building reputation. Therefore, in this paper we propose an assessment mechanism for P2P networks based on reputation to alleviate this problem. A reputation model is also developed to improve the safety of P2P networks by implementing a reputation management method. The rest of the paper is structured as follows. Section 1 describes the proposed mechanism. Section 2 simulates the mechanism and analyzes its performance. Finally, Section 3 concludes the paper.（引言中简单介绍研究背景，针对某些问题的研究现状，这些前人的研究存在某些不足，引出本文的研究。最后一段简单介绍本文的结构）1 Proposed MechanismIn our design, the way of preventing malicious packet dropping in P2P networks is the detection and exclusion mechanism. Neighbor detecting re