一种基于角色PMI的访问控制安全模型

访问控制一直是信息安全的重要保证之一。它包括三种主要的策略，即自主访问控制、强制访问控制和基于角色的访问控制。文中介绍了以上三种访问控制策略以及角色指派属性证书和角色规范属性证书，以此为基础讨论了基于角色的PMI体系结构，然后探讨了基于角色PMI的访问控制安全模型。该模型具有灵活、方便、占用较少存储空间以及减少了网络通信的开销等优点，目前正将该模型使用到大型网络信息管理系统中，实现系统的访问控制。     

多协作证书验证代理系统

提出“多协作证书验证代理”MCCVA概念，可以集中担负验证任务；设计了统一的消息格式，屏蔽已有的验证方式中不同消息格式带来的不便，具有更好的扩充性；给出了多种消息的通信协作机制，具有一定的参考价值。     

电子政务安全建设中的访问控制研究

针对电子政务安全建设过程中的访问控制问题，在重点介绍X．509V4(2000)版属性证书的基础上，提出了一个基于公钥证书身份认证和基于属性证书授权访问的双证书访控模型，并对其进行了分析。     

NPKI-基于嵌套证书的PKI系统

NPKI，即基于嵌套证书的PKI系统，在不改变原有PKI层次结构和信任关系的前提下，优化了证书的证明路径，提高了各级CA的效率，从而有效地弥补了PKI在证书有效性证明中存在的不足。     

基于策略分层的访问控制模型研究

针对分布式环境的访问控制问题，讨论了一种基于策略分层的访问控制模型。该模型利用策略证书和使用条件证书实现分层的访问控制策略，利用公钥证书实现对用户的身份认证，结合角色证书实现对用户的授权访问。     

证书和证书授权

本文主要介绍了证书的基本概念，包括公钥加密机制，数字签名，证书 使用，证书的授 权等，并提供了一个证书样本。     

用移动Agent实现的分布式证书链的搜索

介绍了在分布式环境下的证书管理机制，提出了一种基于移动Agent技术的证书路径搜索模型，给出了模型的体系框架、工作流程和部分实现细节，分析了该模型的性能和实现效率以及尚未解决的问题。     

开放式属性证书及其权限认证策略

针对军内一个大型分布式网络数据库系统的特点，指出了传统权限认证机制的不足。结合先进的属性证书技术，设计了一种开放式属性证书，详述了开放式属性证书的格式、内容及肚于该证粥的认证策略，并阐述了证书的管理和维护。     

网格安全代理系统MyProxy的安全框架

网格的信息安全是其生存和发展的基础，代理是网格安全的基础。详细分析了MyProxy系统的实现原理，提出了安全的MyProxy系统框架。针对MyProxy系统入口（网格门户）的安全和密钥存储的安全，提出了相应的解决方案。在理论上，保证了入口和密钥的安全。     

信用CA证书的设计与应用

在借鉴基于PKI体系的数字CA证书成功经验和模式的基础上，结合信用评测中心提出了“信用CA证书”的设计思想（简称CCA），并探讨了信用CA证书系统的具体操作流程夏其应用，最后对信用CA证书与数字CA证书进行了比较与分析。     

基于OCSP的证书状态查询机制研究与实现

证书状态查询是PKI中的一个十分重要的问题,OCSP是解决这个问题的一种重要机制。分析了OCSP协议,结合Hash快速查找、缓存设计、线程池和Linux内存管理的方法,在保证兼容性、安全性和正确进行数字签名的前提下,提出一种OCSP服务器的实现方法。最后,通过分析证明该系统缩短了平均签名时间,提高了性能。     

Energy-Efficient Redundant Execution of Processes in a Fault-Tolerant Cluster of Servers

This paper investigates into fault tolerance of cluster of servers and their energy efficiency to realize a reliable and energy aware server cluster system. A client issues a request to one server in a server cluster and the server sends a reply to the client in information systems. Once the server stops by fault, the client does not receive a reply of the request. Even if the request is performed on another server on detection of fault of the server, some QoS requirements like response time may not be satisfied. Hence, each request has to be redundantly performed on multiple servers to be tolerant of server faults. The redundant power consumption laxity-based (RPCLB) algorithm is discussed where multiple servers are selected to redundantly and energy-efficiently perform a request process in our previous studies. Since each application process is redundantly performed on more than one server, the larger amount of electric power is consumed. In this paper, we propose a novel and improved RPCLB (IRPCLB) algorithm to reduce the power consumption of servers, where once a process successfully terminates on one server, meaningless redundant processes are forced to terminate on the other servers. In the evaluation, we show the total power consumption of servers and total execution time of processes are reduced in homogeneous and heterogeneous types of clusters by the IRPCLB algorithm than the RPCLB and RR algorithms.     

一种改进的OCSP证书撤销方案

在WPKI中,无线终端设备必须验证服务器证书是否己经撤销.撤销验证是一个复杂的处理过程,因此要选择一个代价较小、简单可靠、适合无线环境的撤销验证方案.在已有的OCSP(On-line Certificate Status Protocol)方案基础上提出一种新的方案,称之为改进的OCSP方案.它是对OCSP协议的改进,能够用较小的代价获得证书的实时状态.给出了这种方案的详细设计,并和其他方案进行了比较.     

Fault detection for Byzantine quorum systems

In this paper, we explore techniques to detect Byzantine server failures in asynchronous replicated data services. Our goal is to detect arbitrary failures of data servers in a system where each client accesses the replicated data at only a subset (quorum) of servers in each operation. In such a system, some correct servers can be out-of-date after a write and can therefore, return values other than the most up-to-date value in response to a client's read request, thus complicating the task of determining the number of faulty servers in the system at any point in time. We initiate the study of detecting server failures in this context, and propose two statistical approaches for estimating the risk posed by faulty servers based on responses to read requests     

WWW集群服务器的数据副本分布方式研究

为了有效地提高WWW服务器的吞吐能力、反应速度和可扩展性,国际上许多著名站点纷纷转向采用WWW集群服务器来替代原有的单一主机服务器.采用不同副本分布方式的WWW集群服务器,其数据可靠性也有所不同.对不同数据副本分布方式进行探讨,同时,论证了最优副本分布方案.     

WPKI中证书撤销验证的代理OCSP方案

在WPKI中,如何在无线终端设备中验证服务器证书是否撤销是一个复杂的问题。对此提出一种新的方案,称之为“代理OCSP方案”。它是对OCSP协议的改进,能够用较小的代价获得证书的实时状态。给出这种方案的详细设计,并和其他方案进行了比较。     

分布式 LDAP 系统的引用研究

LDAP是轻量级目录访问协议的缩写。LDAP是X．500标准在TCP／IP上的实现,它采用树状层次存储结构,树的各层节点就是条目。分布式LDAP系统中,多个LDAP服务器构建不同的域,任何服务器上都可以查询到整个系统的数据。分布式LDAP系统使用引用机制在LDAP服务器间建立连接关系。客户端访问本地服务器查询条目,如果本地服务器发现查询条目不属于本域,它就会根据引用地址访问其他服务器,直至返回被查询条目的数据。但如果客户端查询的条目不在任何域内,则会导致引用死锁,客户端得不到响应,一直处于等待状态。针对上述问题,论文提出增加LDAPMessage字段的解决方案,并测试验证方案可行性。     

Secure dynamic anycasting for ‘best’ server selection using active networks

The networking community has tackled the resource-finding problem using several methods. The knowledge of the name or property of the resource enables one to find it over the network. Many techniques were proposed and investigated for a single instance of the resource. The Internet has experienced dramatic growth in the use and provision of services such as ftp, gopher, archie and World-Wide-Web. The heavy demands being placed on servers inspire replication (mirroring) of servers. This replication results in client intending to contact the ‘best’ server among many content-equivalent servers.

The solutions that were used for the ‘best’ server selection include multicast and broadcast communication to send request to all servers and choose the best one from all the replies. These solutions require the client to be powerful enough to handle all the replies, which may be overwhelming leading to client's machine getting hung. The other solution uses the name servers to provide a different unicast address for one member of a group of servers at different locations. The inherent disadvantage in this method is that the user is unable to choose the best server. The idea of application layer anycasting allows the user to select the best server according to the user's selection criteria. The main disadvantage of this scheme is that the client that does the selection may not be powerful to handle responses from all the content-equivalent servers. In this paper the idea of application layer anycasting has been extended by allowing the active routers to locate the best server. Active networks, unlike the traditional networks are not just passive carrier of bits but instead provides the capability for the user to inject customized programs into the networks that may modify, store or redirect the user data flowing through the network. Anycasting is done in the application level as it provides better end-to-end control, and there is no support in the network level. The choice of ‘best’ server is done based on the first response from the servers. The active routers do the filtering of responses from laggards and the client gets the response only from the best server, thus the client machine is not overwhelmed by responses. The client deals with the vital issue of security with respect to Active networks by the use of various encryption schemes. Since the ‘best’ server chosen is not always the best forever, a TTL value is associated with each of the best server found, and the best one is reselected after its expiry.

The performance of the proposed scheme is compared with the networks without active networks and is found to provide better response time for requests. Further, the proposed scheme avoids the overloading of a server, jockeying, and reduces the overhead of the client in selecting the best server. The overhead on the routers in active networks is insignificant compared to the advantages accrued due to it.     

Optimal Load Distribution for Multiple Heterogeneous Blade Servers in a Cloud Computing Environment

Given a group of heterogeneous blade servers in a cloud computing environment or a data center of a cloud computing provider, each having its own size and speed and its own amount of preloaded special tasks, we are facing the problem of optimal distribution of generic tasks over these blade servers, such that the average response time of generic tasks is minimized. Such performance optimization is important for a cloud computing provider to efficiently utilize all the available resources and to deliver the highest quality of service. We develop a queueing model for a group of heterogeneous blade servers, and formulate and solve the optimal load distribution problem of generic tasks for multiple heterogeneous blade servers in a cloud computing environment in two different situations, namely, special tasks with and without higher priority. Extensive numerical examples and data are demonstrated and some important observations are made. It is found that server sizes, server speeds, task execution requirement, and the arrival rates of special tasks all have significant impact on the average response time of generic tasks, especially when the total arrival rate of generic tasks is large. It is also found that the server size heterogeneity and the server speed heterogeneity do not have much impact on the average response time of generic tasks. Furthermore, larger (smaller, respectively) heterogeneity results in shorter (longer, respectively) average response time of generic tasks.     

线程池设计与动态优化

线程池是提高服务器程序性能的一种很好技术,已经在服务器端应用程序得到了广泛应用,比如Web服务器、数据库服务器、代理服务器和网络游戏服务器等。尤其面对海量并发连接时,线程池对能显著提高系统整体性能。该文提出了一种轻量级的、高效的线程池设计方案,在实际的网络服务器应用应用取得了非常好的效果。