【作者】 朱勤；

【导师】 乐嘉锦；

【作者基本信息】 东华大学 ， 控制理论与控制工程， 2007， 博士

【摘要】 外包数据库技术是信息系统外包服务的技术基础之一。在外包数据库运行模式中,组织或个体将自己的数据库业务外包给数据库服务提供者运行,外包服务提供者为数据拥有者及数据库用户提供远程的数据库创建、存储、更新、查询及数据库服务器软硬件维护与升级等服务。外包数据库运行模式可以实现数据库管理的专业技术对整个社会的共享服务,节约人力物力投资,优化资源配置,并且具有更高的运行维护水平和更好的可扩展性。外包数据库带来的最大挑战就是安全问题。在外包数据库运行模式下,由第三方提供的数据库服务器不处于信任域,存在数据文件盗版、数据内容篡改等安全风险。因此,外包数据库系统的安全机制不但要防止来自外部的攻击,而且要充分考虑来自服务器端的恶意操作,提供对数据库内容的安全保护。现有的数据库内容保护技术通常采用密码学方法来实现。数据的加密解密及密钥管理机制均涉及比较复杂的运算过程,在一定程度上限制了数据库系统的可用性;密文的随机性同时也暴露了消息的重要性,造成了新的不安全性;密文数据一旦被解密,则加密机制对数据库内容的安全保护失去任何作用;基于密码学方法的数字签名等技术通过添加冗余验证信息来保持数据内容的完整性,由于验证信息与被保护数据分离,容易被删除而失去安全保护能力。为克服现有解决方案的不足,本文提出基于数据库水印技术的外包数据库系统内容保护解决方案。数据库水印是指用信号处理的方法在数据库中嵌入不易察觉且难以去除的标记,在不破坏数据库可用性的前提下,达到保护数据库安全的目的。数据库水印技术并不限制正常的数据存取,而是提供对数据库的所有权证明与内容完整性验证,从而对数据窃取与攻击行为起到电子举证的作用。同时,数据库水印可以和密码学方法结合使用以增强数据库系统的安全性。本文主要研究数据库水印技术及其在外包数据库内容保护方面的应用。建立数据库水印的理论框架,设计数据库鲁棒水印、数字指纹与脆弱水印算法及相应的数据库水印协议,开发原型系统,实现对外包数据库的版权认证、法及相应的数据库水印协议,开发原型系统,实现对外包数据库的版权认证、盗版追踪及查询验证。理论分析与实验结果表明,基于数字水印的外包数据库内容保护技术较好地满足了系统的安全性与可用性需求。本文的研究工作主要包括以下五个方面,其中第2、3、4三个方面为本文的主要创新点;1)数据库水印模型与基本理论的研究。由于数据库水印研究的历史不长,目前尚未形成成熟的理论框架。本文给出了数据库水印的定义,建立数据库水印的形式化模型,分析数据库水印的主要特征与分类方法,归纳其应用领域;描述数据库水印系统的框架结构,分析数据库水印的基本技术,包括水印信号、水印载体信道、元组标记、水印嵌入、水印检测与提取,总结这些技术的主要特点与实现方法,并进行对比与评价;列举常见的数据库水印攻击形式,给出相应的防范对策;提出数据库水印性能评估的指标体系,阐述了主要性能指标间的制衡关系,给出了部分指标的定量计算方法。2)基于鲁棒水印的数据库版权认证技术的研究。鲁棒水印是进行版权认证常用的技术。现有的数据库鲁棒水印算法存在抗攻击能力弱、误差控制粗糙、易产生病态结果等缺点。本文将混沌序列用于数据库水印,通过修改数值属性低位数值的奇偶性嵌入水印,克服了现有的LSB替换算法易产生病态现象的缺点,获得了更好的鲁棒性与隐蔽性。该算法利用混沌系统的初值敏感性和迭代不重复性,采用随机混沌序列结合数据库元组主键及密钥产生多位水印信号;水印的嵌入与检测只与密钥及当前元组有关,满足数据库动态更新的同步要求;水印的检测无需原始载体数据参与,实现了水印的盲检测。3)基于数字指纹的外包数据库盗版追踪技术的研究。为约束多个外包服务提供者间合谋进行的盗版行为,需要有相应的安全机制能追踪盗版数据库的来源。应用鲁棒水印仅能解决盗版数据版权识别的问题,而应用抗合谋数字指纹技术可以实现对合谋用户的叛逆追踪。现有的数据库指纹算法存在版权认证与盗版追踪脱节,指纹检测运算量大等不足。本文基于C-安全码的编码框架,提出了一种结合版权水印的抗合谋数据库指纹编码方案,设计了相应的指纹生成与嵌入、指纹检测及叛逆追踪算法。由于将版权水印引入指纹编码,降低了指纹检测与叛逆追踪的运算复杂度。4)基于脆弱水印的外包数据库查询验证技术的研究。由于外包数据库服务器运行在不完全可信的第三方,来自服务器端的攻击者可能会对数据库添加虚假记录,或篡改已有记录,这就需要对数据库内容是否真实有效进行验证。针对传统的基于添加冗余验证信息的解决方案的不足,本文提出一种基于脆弱水印的外包数据库查询验证方案。以连接多项式数组为密钥生成m序列,分别作为水印信号和水印嵌入策略控制信号,通过修改数值属性低位数值的奇偶性嵌入脆弱水印。数据库用户向服务器提交查询请求后,利用数据拥有者提供的密钥,对返回的查询结果运行水印检测算法,进行数据真实性验证。该方案解决了“统一客户端模式”下外包数据库投影—选择类查询的真实性验证问题。由于通过脆弱水印将验证信息包含于被保护内容中,冗余存储量与网络附加负载小,验证信息难以删除,能实现元组属性粒度的篡改定位。5)基于数字水印的外包数据库内容保护系统设计与实现。本文基于数据库鲁棒水印、数字指纹及脆弱水印算法,综合应用数字水印、PKI体系结构、数字签名及USB Key技术,设计相应的水印协议,构建了一个网络环境下的外包数据库内容保护系统,实现了外包数据库版权认证、盗版追踪及查询验证等功能。系统借助PKI机制实现了身份认证、数字证书签发、可信时戳等安全服务;将数据库水印技术与加密、数字签名等技术结合,弥补了水印在主动安全保护方面的不足;数据库水印协议的设计满足了数据库数据容量大、更新频繁的特点,具有抵抗多种水印攻击的能力;可信硬件模块USB Key的引入,增强了系统保护数据及安全交互的能力。本文的研究工作存在的不足之处主要包括;所提出的数据库鲁棒水印算法主要适用于能够容忍一定精度范围数据失真的数值型属性数据;所提出的外包数据库指纹解决方案是一种对称指纹机制,未能实现对无辜用户的防陷害性;所构建的基于数字水印的外包数据库内容保护系统以第三方可信计算平台的安全性为基础,存在一定的安全失效风险。与传统的直接通过数据加密、数字签名等技术进行数据库内容保护的方法相比,基于数字水印的数据库内容保护技术具有冗余存储量及网络附加流量小、隐蔽性好、能实现较小粒度的篡改定位、易于实现等优点,是一种在开放的网络环境下,从非加密角度进行数据库安全控制的新策略,有较高的研究价值和较好的应用前景。更多还原

【Abstract】 Outsourced database technology is the basic ingredient of the infrastructure of outsourced information system service. In outsourced database system, the organizations or individuals outsource their database business to the service provider, which offers mechanisms of creating, storing, updating and querying database to the data owner and the database users, as well as maintaining both the software and hardware of database server. The outsourced database scheme can share the professional database management services to whole society, save the investment for human resource and material resource, optimize the resources allocation, and get the better running performances and expansibility.The greatest challenge that the outsourced database faces is its security issue. In outsourced database scheme, since the database server, which is provided by the third part, is not in the trust domain, the data files take the risk of being pirated, as well as the data contents being tampered with. So the secure scheme of the outsourced database system needs to prevent the database from not only attacks coming from the outside, but also malicious operations coming from the server side.Current technologies of database contents protection are mostly implemented via cryptography. Since the data encryption, data decryption and the key management scheme involve complicate computing procedure, the availability of the encrypted database system is limited; The randomization of encrypted data may betray the importance of the message, thus results in new insecurity; Once the encrypted data are decrypted, the cryptography loses its protective function for database contents; The cryptography based digital signature technology authenticates the integrity of database contents by adding redundant verification message, which can by removed due to being separated form the sheltered data.To overcome shortcomings mentioned above, a novel solution for outsourced database contents protection based on database watermarking is proposed in this thesis. Database watermarking, which embeds implicit and un-removable marks in database through the method of signal processing, reaches the aim of protecting the database security without damaging the content and the availability of database. What the technology of database watermarking can provide are the abilities of proving the ownership of the database, verifying the integrity of the data contents and presenting the electronic evidences for accusing the piracy and attack to the database, rather than constraining regular data accessing. Meanwhile, database watermarking can work conjointly with cryptography to reinforce database security.This thesis focuses on the technologies of database watermarking and its application in outsourced database contents protection. The theoretical framework of database watermarking is established. The algorithms of database robust watermark, digital fingerprint and fragile watermark, as well as the corresponding watermarking protocols, are designed. The prototype system, which realizes the copyright certification, traitor tracing and query authentication, is developed. Both the theoretical analysis and the practical experiments prove that the technology of outsourced database contents protection based on watermarking meets the system requirements for both the security and the availability.Work in this thesis mainly consists of the following five aspects, among them the second, the third and the forth one include the key innovative ideas:1) Research on formalized model and basic theories of database watermarking. Due to the short history of research, the maturational theoretical framework for database watermarking has not been formed so far. In this thesis, the definition of database watermarking is presented, the formalized model is established, the main properties and catalog approach are analyzed, and the application areas are generalized. The architecture of database watermarking system is described, the basic technologies of database watermarking, including watermark signals, watermark carrier channels, tuple marking, watermark embedment, watermark detection and extraction, are explained, as well as their special features and implement methods are summarized, compared and evaluated. Common types of attacks towards database watermark are listed, meanwhile, the preventive methods against them are proposed. The metric hierarchy for evaluating the performances of database watermark is presented, the balance relations between these performances are exposed, and some computational methods are provided.2) Research on database copyright certification based on robust watermark. Robust watermark is commonly used in copyright certification. Traditional algorithms of database robust watermarking have their shortcomings, including weak attack- resisting, coarse error-control, and being prone to syndrome phenomena. In this thesis, chaotic sequences are applied in database watermarking, the watermarks are embedded into the numeric data by changing their parity of the low order numbers, thus avoids the syndrome phenomena caused by the usual Least Significant Bit (LSB) watermarking algorithm, and gets better robustness and imperceptibility. Based on its properties of non-repetitive iterative operation and sensitiveness to the initial input, the chaos system is applied to generate multi-bit watermark signals according to the primary keys of the database tuples and the randomized chaotic sequences under the control of the secret key. The process of embedding and detecting watermarks needs only the secret key and the current tuple, thus meets the requirement of the database for synchronous dynamic updating. The detection of watermarks need no original database, thus realizes the blind-detection.3) Research on outsourced database traitor tracing based on digital fingerprint. In order to prevent the outsourced service providers from pirating database via collusion, it is necessary to deploy secure scheme for tracing the original source of the pirate copy. The technology of robust watermark can be used to certificate copyright of database, while the technology of anti-collusion fingerprinting can be used to tracing the traitors among collusive users. Traditional algorithms of database fingerprinting have their shortcomings, including disjointed relation between copyright certification and traitor tracing, and high computational density of fingerprint detection. In this thesis, a scheme of anti-collusion database fingerprinting, which is based on the C-Secure Coding framework and combined with copyright watermark, is proposed. The corresponding algorithms of fingerprint generation, fingerprint embedment, fingerprint detection and traitor tracing are designed. Due to the copyright watermark being introduced into the fingerprint coding, the computational complexities of fingerprint detection and traitor tracing are degraded.4) Research on outsourced query authentication based on fragile watermark. Since the outsourced database server runs at third party that cannot be fully trusted, attackers from server side may add forged tuples into the database or tamper with the database, it is necessary to verify the validity and integrity of the database contents. To overcome shortcomings of traditional solutions that mainly based on redundant authentication coding, a novel scheme of outsourced database query authentication based on fragile watermark is proposed in this thesis. The m sequences are generated based on the secret key coming from a connection polynomial array, and are used for the watermark signals and the control signals for watermark embedment. The fragile watermarks are embedded into the numeric data by changing the parity of their low order numbers. When the database user receives his query results from the server, the data are verified by detecting the watermarks in the result set using the secret key, which is provided by the data owner. This solution is applicable to the validity authentication for projection-selection query under the Unified Client Model of outsourced database. Since the authentication information is embodied in the fragile watermark, the redundant storage capacity and communication flow are little, the authentication information is hard to be removed, and the tamper with the database can be located at the grain of tuple attribute.5) Design and implement of contents protection system for outsourced database based on digital watermark. In this thesis, a system for outsourced database contents protection in network environment is built, which is based on algorithms of database robust watermarking, digital fingerprinting and fragile watermarking, as well as their corresponding protocols, and is combined with technologies of PKI (public key infrastructure), digital signature and USB Key. The system performs such functions as copyright certification, traitor tracing and query authentication for outsourced database. In the built system, such secure services, as identity authentication, digital credential issuing, trusted time stamp service, are implemented via PKI scheme. The watermarking is combined with data encryption and signature, thus makes up the watermarking for its shortcoming in active protection. The design of watermarking protocols meets the requirements of database system for mass data and frequent updating, as well as the ability for resisting common attacks towards watermarks. As a trusted hardware module, the USB Key reinforces the data protection and the secure communication.There are some shortcomings in this thesis. The proposed algorithm of database robust watermarking is only applicable for numeric attributes that can tolerate somewhat distortion within curtain extent; The proposed solution of outsourced database fingerprinting is based on the symmetric fingerprinting scheme, which cannot perform the function of preventing legal users from being framed; The security of the built system for outsourced database contents protection is based on the security of third trusted party, thus would be a certain amount of security risk.Compared with traditional solutions of data encryption or digital signature, the technology of watermark-based database contents protection possesses the advantages of less redundant capacity either for storage or for communication, better imperceptibility, more fine grain for locating tamper, and easier to implement. Therefore, it is a novel technique for database security in the opening networks via non-cryptography, and it illustrates a good prospect of research and application.更多还原