针对实时数据库中隐蔽通道问题采取的安全策略

实时数据库的根本目标就是使满足截止时间的事务数为最大,因而,管理和支持优先考虑时间的事务处理是非常重要的。然而,随着实时计算的迅速发展,安全成了实时应用另一个必须考虑的问题。因此,在实时数据库系统中,提出一种结合实时性和安全性的方法是非常必要的。本文针对隐蔽通道讨论了安全问题。通过定义的CCF、DCCF变量对实时数据库中的并发控制算法进行扩展使其既满足时间限制条件又满足安全需求。陈述了消除隐蔽通道的非干预性原则,并对同时维持实时和安全需求的可行性进行了探讨。     

实时数据库的安全并发控制策略

为了解决实时数据库系统中事务的实时性和安全性之间的矛盾,文中首先分析安全实时数据库系统中实时性与安全性需求之间的冲突,而后基于HP-2PL协议,结合安全因素给出了一种解决冲突的办法。在满足安全需求的基础上,实现数据库的安全实时性能。     

实时数据库的安全并发控制

为了解决实时数据库系统中事务的实时性和安全性之间的矛盾,文中首先分析安全实时数据库系统中实时性与安全性需求之间的冲突,而后基于HP-2PL协议,结合安全因素给出了一种解决冲突的办法。在满足安全需求的基础上,实现数据库的安全实时性能。     

一种面向主动对象的实时数据模型

针对支持复杂实时应用的实时数据库管理系统,提出了一种面向主动对象的实时数据模型AOORT,将面向对象实时性和主动性更好地集成在一起。模型由对象、关系和规则3部分组成。对象用来对带有时间特性的实体进行建模,扩展了传统对象来提供实时和主动特征;关系描述了对象之间的联系情况;规则体现了数据库的主动性,并集成了时间约束。最后以一个简单网络化控制系统中的实时数据采集和监控子系统为例,展示了AOORT模型的具体应用。     

一种基于乐观方法的安全实时并发控制协议

实时数据库通常应用在一些安全关键类应用中,如电子商务、股票交易、军事指挥系统等。在这样一些应用中,实时数据库系统需同时满足两方面的需求：确保数据安全和尽可能减低实时事务错过截止期的比率。然而,通常这两方面需求是相互冲突的,满足一方面是以牺牲另一方面为代价。本文提出了一种基于乐观方法的安全实时并发控制协议,该协议将安全约束整合到实时乐观并发控制协议中,并能根据应用的需求在安全性和实时性方面进行了适当的折中。性能测试结果显示,该协议在确保数据安全的同时并未明显地降低实时性能。     

Real-TimeSQL的设计与实现

实时数据库的结构化查询语言RTSQL(Real-TimeSQL)是实时数据库研究的一项重要内容。论文详细论述了RTSQL的一种设计方法,即扩展SQL92标准以支持实时数据库的要求,构建RTSQL语言的方法。文章还介绍了RTSQL在Agilor实时数据库系统中的实现方式。在文章最后给出了RTSQL进一步研究的思路和建议。     

嵌入式实时数据库研究与实现

嵌入式实时数据库系统是指可在嵌入式设备中独立运行的一种数据库管理系统,以高可靠性、高实时性和高信息吞吐量为目标,其数据的正确性不仅依赖于逻辑结果,而且依赖于逻辑结果产生的时间.通过对嵌入式实时数据库关键技术研究,基于嵌入式Linux平台设计与实现了一个嵌入式实时数据库原型系统--ERDB,该系统实现结构化查询语言SQL-92子集,采用抢占式事务管理技术,当系统检测到实时事务时,优先调度执行实时事务,从而满足实时性能需求.     

工控组态软件实时数据库系统的开发与设计

针对组态软件实时数据库的实时性不强、购买成本高等不利因素,以Visual C++6.0为开发工具,采用传统数据库系统、文件系统和内存数据库系统兼用、多种存储介质相结合的方式,以动态链接库技术构建了一种实时性较强的实时数据库系统.提出利用面向对象技术的类来存储实时数据库的变量,给出了数据模型和开放接口的实现方法.实际应用结果表明,建立的实时数据库系统具有较强的开放性与实时性.     

基于多版本的安全实时并发控制协议

安全实时数据库必须同时满足安全性和实时性,然而这两者有时可能相互冲突.为了解决这种冲突,提出了基于多版本的安全实时并发控制协议.协议为每个数据对象提供两个版本:工作版本和只读版本,根据事务和数据对象的安全级为事务提供不同的数据版本,有效地解决了实时性与安全性之间的冲突,最后给出了协议的正确性证明.     

一种面向嵌入式实时系统的安全策略优化生成方法

由于受到系统资源和实时性的限制,对于嵌入式实时系统的安全扩展很难延用通用计算机系统的安全设计方法,因此需要对其进行专门的研究。为了在确保实时性的前提下使嵌入式实时系统的安全性达到最优,本文提出了一套完整的安全设计方法,包括安全任务图模型和安全评估模型,在此基础上,又提出了一种基于整数线性规划的安全策略优化生成方法ILPOS。该安全策略优化生成方法同时解决了安全算法选择和实时可调度性检测两方面的问题,克服了一般分阶段优化方法的不足,从而充分地利用系统可用时间来实现安全扩展。仿真实验结果表明,与传统的启发式安全设计算法相比,ILPOS方法在各种实时性约束条件下都能有效地提高系统的安全性。     

Issues and approaches to supporting timeliness and security in real-time database systems

Databases for real-time systems are essential in supporting time-critical applications. However, there has not been much work in supporting security in real-time database systems, although sensitive information must be safeguarded in real-time systems as well. In this paper we address the issues that need to be considered for supporting both requirements of timeliness and security in real-time database systems. We present an adaptive policy to achieve the balance between the two requirements dynamically. We also present the notion of flexible security and the specification language that allows the designer to specify important properties of the database at an appropriate level.     

Integrating security and real-time requirements using covertchannel capacity

Database systems for real-time applications must satisfy timing constraints associated with transactions in addition to maintaining data consistency. In addition to real-time requirements, security is usually required in many applications. Multi-level security requirements introduce a new dimension to transaction processing in real-time database systems. In this paper, we argue that, due to the conflicting goals of each requirement, tradeoffs need to be made between security and timeliness. We first define mutual information, a measure of the degree to which security is being satisfied by a system. A secure two-phase locking protocol is then described and a scheme is proposed to allow partial violations of security for improved timeliness. Analytical expressions for the mutual information of the resultant covert channel are derived, and a feedback control scheme is proposed that does not allow the mutual information to exceed a specified upper bound. Results showing the efficacy of the scheme obtained through simulation experiments are also discussed     

Multiversion locking protocol with freezing for secure real-time database systems

Database systems for real-time applications must satisfy timing constraints associated with transactions. Typically, a timing constraint is expressed in the form of a deadline and is represented as a priority to be used by schedulers. Recently, security has become another important issue in many real-time applications. In many systems, sensitive information is shared by multiple users with different levels of security clearance. As more advanced database systems are being used in applications that need to support timeliness while managing sensitive information, there is an urgent need to develop protocols for concurrency control in transaction management that satisfy both timing and security requirements. In this paper, we propose a new multiversion concurrency control protocol that ensures that both security and real-time requirements are met. The proposed protocol is primarily based on locking. However, in order to satisfy timing constraints and security requirements, a new method, called the freezing method, is proposed. In order to show that our protocol provides a higher degree of concurrency than existing multiversion protocols, we define a new serializability for multiversion concurrency control, called FR-serializability, which is more general than traditional serializability. We present several examples to illustrate the behavior of our protocol, along with performance comparisons with other protocols. The simulation results show significant performance improvement of the new protocol.     

嵌入式数据库系统中无冲突并发控制协议CCCP

嵌入式实时数据库系统不仅需要较高的成功率．而且往往是在无人工干预的情况下运行，要求事务具备自我调节能力和较强的适应能力．事务必须支持功能替代性，在并发控制策略CCCP中，替代成为并发控制的主体．对于每个实时事务，一个最适合当前运行环境的替代以无冲突的方式调度执行．CCCP基于替代的优先级，对替代进行相容性分析，保护就绪事务，并且有一种开销较低的实现算法．性能分析证明CCCP有利于优选替代，从而有利于提高系统的成功率，适用于嵌入式实时数据库系统．     

RealNet: a neural network architecture for real-time systems scheduling

Real-time embedded systems are spreading to more and more new fields and their scope and complexity have grown dramatically in the last few years. Nowadays, real-time embedded computers or controllers can be found everywhere, both in very simple devices used in everyday life and in professional environments. Real-time embedded systems have to take into account robustness, safety and timeliness. The most-used schedulability analysis is the worst-case response time proposed by Joseph and Pandya (Comput J 29:390–395,1986). This test provides a bivaluated response (yes/no) indicating whether the processes will meet their corresponding deadlines or not. Nevertheless, sometimes the real-time designer might want to know, more exactly, the probability of the processes meeting their deadlines, in order to assess the risk of a failed scheduling depending on critical requirements of the processes. This paper presents RealNet, a neural network architecture that will generate schedules from timing requirements of a real-time system. The RealNet simulator will provide the designer, after iterating and averaging over some trials, an estimation of the probability that the system will not meet the deadlines. Moreover, the knowledge of the critical processes in these schedules will allow the designer to decide whether changes in the implementation are required.This revised version was published online in November 2004 with a correction to the accepted date.     

满足嵌入式实时数据库系统的可预见能力

可预见能力是嵌入式实时数据库系统必须具备的特性，目前还未发现有关的研究报道，我们研制的嵌入式实时数据库系统主要从四个方面提高系统的可预见能力，存取扩展数据，使系统内部控制可见，便于透明地处理系统纠偏；基于功能替代的实时事务模型，它支持方案多选，具有丰富的可预见描述能力，支持事件驱动的主动触发机制，能对系统的瞬时发生作出应急反应，多层次的实时事务调度，能大大提高实时事务对动态实时环境的的应变能力和系统的成功率。     

Designing secure databases

Security is an important issue that must be considered as a fundamental requirement in information systems development, and particularly in database design. Therefore security, as a further quality property of software, must be tackled at all stages of the development. The most extended secure database model is the multilevel model, which permits the classification of information according to its confidentiality, and considers mandatory access control. Nevertheless, the problem is that no database design methodologies that consider security (and therefore secure database models) across the entire life cycle, particularly at the earliest stages currently exist. Therefore it is not possible to design secure databases appropriately. Our aim is to solve this problem by proposing a methodology for the design of secure databases. In addition to this methodology, we have defined some models that allow us to include security information in the database model, and a constraint language to define security constraints. As a result, we can specify a fine-grained classification of the information, defining with a high degree of accuracy which properties each user has to own in order to be able to access each piece of information. The methodology consists of four stages: requirements gathering; database analysis; multilevel relational logical design; and specific logical design. The first three stages define activities to analyze and design a secure database, thus producing a general secure database model. The last stage is made up of activities that adapt the general secure data model to one of the most popular secure database management systems: Oracle9i Label Security. This methodology has been used in a genuine case by the Data Processing Center of Provincial Government. In order to support the methodology, we have implemented an extension of Rational Rose, including and managing security information and constraints in the first stages of the methodology.     

不可否认协议分析的扩展ZQZ逻辑方法

不可否认协议必须满足存活性、不可否认性、公平性和时限性,但当前大多数形式化方法只能分析该类协议的部分性质,证明或证伪协议逻辑的部分正确性.本文通过向ZQZ逻辑添加时间表达式,提出了一种适用于不可否认协议建模与分析的扩展ZQZ逻辑方法,包括推理规则和安全性质模型.展示新方法的应用时,使用其分析了ZG和KPB这两个局部逻辑正确性已知的两方不可否认协议,以及YLL这个逻辑正确性尚在讨论的基于区块链的多方不可否认协议.实验显示,对前两个协议的分析结果与既有事实相符,对第三个协议的分析发现其无法为收方提供设计者所宣称的时限性.以上结论从逆向工程角度佐证了扩展ZQZ逻辑方法是一种行之有效的不可否认协议分析新方法.