摘要
密态数据库技术是密码学[Stallings W，2001；Atul Kahate,2005]与数据库[Chaudhuri S．，2001；Haraty，2003；Preston Carole，2002；Bettino Elisa，2002]技术的融合，在这个结合的技术中，人们在方便使用数据库技术的同时，存储的数据得到更加安全的保密。但是这种结合的技术带来了新的问题。由于加密后的数据库通常不再具有原先的特性，传统的数据库操作将不能用于密态数据库。另外，数据库的加密也将给查询、运算等的执行效率产生较坏的影响。在密态数据库环境中，为了向用户提供信息服务，系统通常需要通过解密获得原始信息。但从另一个方面来看，数据库解密后，就将导致大量的用户数据暴露。因此同态[Rivest,1978；Domingo-Ferrer,1996]运算将是密态数据库实施所面临的最主要研究问题。
加密[Bruce Schneier，1996]模型、密钥管理[Damiani，Ernesto,2005]、同态操作和密态处理[Domingo-Ferrer，1997；N．Ahituv，1987；Wu Xintao,2005]以及有效利用是密态数据库研究的主要任务。
建立合适的密态数据库加密模型需要考虑两个主要问题：一是要考虑加密的粒度和加密的层次；二是要考虑操作的效率，即在安全性和易用性方面寻找平衡点。为了建立加密模型，主要讨论了数据库的基本结构、数据库系统的层次模型以及操作效率等问题。
密态数据库的安全保障主要取决于在密文下处理数据。同态操作概念的提出使我们有信心直接进行密文运算。但目前的情形只适合算术运算，并且算法有缺陷。
密态数据库下利用密码学技术加密数据，其决定安全性的密钥管理及生成问题也是期待较好解决的问题。
密态处理使我们保证数据库安全性的同时为用户提供数据挖掘和个性化服务。
有效利用是我们研究密态数据库理论的最终目标。
本文在收集和分析大量近年来国内外数据库安全方面的研究报告学术论文等专业资料的基础上对数据库安全所涉及的若干理论问题包括密文挖掘等问题进行了探讨。主要工作包括：
1．对数据库系统的理论进行了研究，分析了其不安全性的产生原因并讨论了各种解决方法。包括从操作系统底层进行安全保护和从其上层进行安全控制的实现方法，并分析了其优缺点。结论是必须根据特定应用的要求进行正确选择，从而在安全性和易用性方面实现权衡。为进一步研究密态安全数据库问题提供了基础和研究角度。
2．分析了目前已有的密文索引模型，提出了一个较安全的改进性控制方法。该方法通过平均差值排序来隐藏明文序列。对字段级加密，通过引入干扰因子来隐藏信息的泄露。并对可能出现的有限值域信息泄露进行了研究。对文献[5]提出的防泄露算法进行了分析。通过实验结果表明：文中提出的方法在增强数据安全的同时，也具有较短的响应时间。采用将数据置乱，尽量避免使用指针以防止泄露联系，存储位置的联系完全取决于函数依赖。研究各种变换技术所产生的算术运算效果。
3．对安全数据库系统中的密态操作问题进行了研究，文献[戴一奇等，1997；崔国华等，2000]提出一种索引机制，但安全性和任务分配存在问题。文献[杨勇等，2005；王晓峰等，2003]提出用一种秘密同态的技术解决此问题。但如何实际实现未提及。提出了基于秘密同态的实现模型，分析了整数算术同态和实数算术同态的实现。在代数范围内对同态变换进行了研究。为实现加密数据的比较运算，保序加密理论提出了一种解决方法，并分析了其各自的特点。提出一种改进的同态操作算法，该算法避免了E(m_1)-E(m_2)=m_1-m_2的缺陷。
4．针对目前的C／S模式的数据库应用系统提出了实现安全科学计算的一种新的途径。根据实际应用，结合各种方法之优缺点，提出依靠Matlab系统通过秘密同态和安全套接层来保证科学计算中数据的安全性。并提出基于数据库的在线改进计算模型，借助秘密同态来实现安全算术运算。对如何提高在线安全计算提供了一个可参考的方法。在线实现WEB技术是指服务端根据客户端的请求自动生成新的相应页面．相应页面在服务端完成后，传至客户端。数据的处理在服务端执行。
5．基于密态的数据挖掘是安全数据库应用系统中的另一个重要研究领域。对实现隐私保护的数据挖掘提供了一种解决途径。分析了数据挖掘理论及在密态下的实现途径。为了解决这个问题，我们引入第三方代理。首先，将需要挖掘的部分加密后传送到代理，以避免代理泄露数据。如果服务商需要执行相关的数据挖掘，就发送请求到第三方。代理在密态下执行运算。最后代理将加密的结果传送给服务商，服务商通过解密获取结果。
6．研究了利用手写体技术自动生成密钥的问题。基于手写体特征的密钥生成将生物特征与应用密码有机结合。使在生成安全便利密钥的同时，加入了用户的个性化特征，进一步增强了信息系统的安全性。
概括起来，本论文在分析数据库理论和已有的密态理论基础上，探讨了其运行机理，并在相关理论改进和应用方面作了许多工作，为数据库安全增添了新的血液。进一步深入研究其理论基础和拓宽其应用领域是今后工作的研究重点和发展方向。
With the technical development of computer, the great important data is processed through computer and saved to storage.The computer suffers the attack of the external world easily. Therefore the safety of database has the higher realistic meaning and theories meanings.The security of database information become the key part of the modern information.The acquired achievements of this dissertation are summarized as follows:
A. Study on database system
This paper Carry on the research to the theories of the database system, analyze its insecurity reason and discuss various solve the method.
B. In order to imp rove database security, and to avoid information exposing of access control strategy, data item was used as the encryp ted p rincip le, app lying its p roperty of basic granularity to strengthen the database security. Some solved method was given in the database currently. A new query algorithm was used to acquire imp roved encryp ted data. The p roposed algorithm uses average-value as p rincip le to conceal the clear statement sequence. For field encryp tion, the information exposing was avoided by interference factor. A kind of information exposure of encryp ted database was given in limited value area. The simulation results p roved that the database security ofmodified method is higher than other method, and modified method has shorter response time.
C. Encryp ted database are an effective method to realize database security. A quick index is raised in paper [Dai Yiqi, 1997].But there isdeficiency about security and task allocation. Privacy homomorphism is raised to discuss this p roblem in paper [Yang Yong, 2005]. A module based on p rivacy homomorphism is presented, and mathematic method on p rivacy homomorphism is discussed. It is p roved that thismethod is impossible in the range of the real, and a new operation must be defined.
D. How to improve secure computing is a important problem in science computing. This paper analyzes dynamic network technique and Web system of Matlab firstly. Then put forward the improvement project of the database for the purpose of the further analysis. It puts a referenced method to how to improve secure computing.
E. A Modified Model for Secure Database.
In order to improve personal data security in database, and to avoid information exposing of personal privacy, personal data was used as the encrypted principle, applying homomorphism and random perturbation to strengthen personal data security. This paper analyze the usage of personal data in electronic commerce firstly, Then discuss realization security of personal data. In light of this, a new algorithm was used to acquire improved security. The proposed algorithm uses homomorphism as principle to preserve privacy. This method can make the important data to be appeared with secret content in the web service, and prevent personal data from being misused. The simulation results proved that the modified method can protect personal privacy effectively, and can carry on data mining to provide the characteristic service for the customer, and modified method has shorter response time.
F. Study on automatic key-generation based on speech technique.
Summarily, the dissertation does a great deal of work in the aspect of studying encrypted database theory and applications, while having acquired many achievements of which inject new blood for secure database. Besides, these models will be further enriched and consummated. Our research, from now on, will be focused on compressively studying their theoretical foundations and exploring their applying area.
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