【作者】 任一支；

【导师】 李明楚； 樱井幸一；

【作者基本信息】 大连理工大学 ， 计算机软件与理论， 2010， 博士

【摘要】 近些年来,随着互联网技术的迅速发展,出现了许多大规模的分布式应用系统,如普适计算、网格、对等网络、Ad Hoc等。由于这类分布式应用系统的动态性、开放性、自治性等特性,使得主体在面对传统安全威胁同时,还要经常面对陌生的、理性的合作对象,从而出现了诸如“搭便车”、“公共悲剧”以及“资源不可信”等现象。这大大增加了主体利益受到新侵害的风险。因此,如何保护此类新环境下主体间可信性(例如,安全性,公平性等)成为近来研究的热点。在此背景下,作为研究的重点方向之一,研究人员提出了信任(誉)管理等相关技术,旨在通过“软安全”方法来保障开放环境中主体面临的可信性问题。本文针对现有信誉系统研究中存在的问题,主要从信任评估粒度、主体合作理论以及主体信任结构等三个方面展开,并提出了问题的解决方案。其主要贡献如下：(1)在信任评估的粒度研究中,针对如何选择合适的推荐主体以及分析其推荐信息的可靠性等两大问题,提出了一种细粒度信任计算模型。该模型将服务质量进行细粒度化,在选择推荐主体时,通过定义朋友因子来反映主体间关系的亲疏,从而选择合适的推荐主体。在分析推荐信息时,通过分析主体的即时状态、推荐错误以及偏好相似性等信息,从而提高推荐信息的精确性。相关实验结果表明,当服务质量的维数增加时,该模型可以有效地抑制恶意主体。(2)在主体合作理论研究中,针对在信誉系统中如何促使主体间合作产生的问题,提出了一种基于群体的方案。该方案以群体选择理论为基础,将信誉系统中主体依据其存在的社会联系分成独立的“群体”,并从主体层次和群体层次来分析了其演化动态性。相关实验表明,该方案可以有效地抑制不合作主体。(3)在主体信任结构研究中,针对主体信任结构对于系统安全影响的问题,提出了一种利用信任思想来分析桥式信任结构安全性的方法,该方法将现有桥式信任结构抽象成(m,n)星型结构,并证明了(m,n)桥式信任结构“扮演风险”上限为1-(n-1)/2mn,据此,给出了现有桥式信任结构修改方案。更多还原

【Abstract】 With the development of Internet technologies, it emerges a lot of large scale distributed systems, such as Ubiquitous computing, Grid computing, Peer-to-Peer (P2P) computing, Ad hoc networks, etc. Because of the dynamics, openness and autonomy nature of these systems, it may harm users’ benefit under the increasing risks. Therefore, there are big challenges how to solve the trust issues (e.g., security, fairness) among participants in this kind of environment. Reputation systems which designed to address these problems represent a significant trend in decision support for internet mediated service provision. The basic idea is to let parties rate each other after the completion of an interaction, and use the aggregated ratings about a given party to derive a reputation score, which can assist other parties in deciding whether or not interact with that party in near future. Facing the weakness of the existing work, in this dissertation, we highlight several key research topics, such as, granularity of trust evaluation, cooperation theory and trust overlay.The contributions of this dissertation are list as follows:(1) Granularity of Trust Evaluation. We propose a fine-grained trust computation model for P2P networks. Our model defines the service as a fined-grained quality-of-service (QoS) (N-dimensional vector), and in order to accurate the recommendation trust computing, several concepts are introduced to reflect the recommenders’current status, history behavior, and the gap between these two behaviors. Also, we firstly introduce the Gauss-bar function to measure the preference similarity between peers. All these will result in a flexible model which represents trust in a manner more close to human intuitions and satisfies the diverse QoS requirements of peers in P2P networks.(2) Cooperation Theory. We propose a group-based scheme to enhance cooperation for online reputation systems. In this section, we define related concepts to capture the social structure and ties among participants in reputation system, e.g., group, assortativity, etc. Also, we use Femi distribution function to reflect the bounded rationality of participants and the existing of stochastic factors in evolutionary process.(3) Trust Overlay. We propose two methods to analyze structured trust overlay and un-structured trust overlay, repectively. In the first method, we analyze the security issues in PKI trust model, especially for Bridge Certificate Authorities (BCA), by using the concept of "impersonation risk", and prove the upper of "impersonation risk" of BCA trust model is 1-(n-1)/2mn. Based on that, we finally propose a new modified BCA model, which enhances its security, but a bit more complex in certificate path building and implementation than existing one. In the seconde method, we develop a mathematical framework to analyze the stochastic dynamics of trust structure, which enabling agents to change. Our method can instruct to how enhance agent cooperation, or design reward and punishment mechanisms in open networks.更多还原