Using Cryptography to Control Access in Published Data

通过XML文档进行信息交换是一项快速发展的技术。然而，迄今为止，信任和保密方面的复杂限制往往禁止数据的传播。可以安全地传播给其他人的数据仍然隐藏在防火墙后面。该项目旨在生产轻量级工具，允许发布和传播数据，同时控制访问数据的方式。为了在已发布的XML文档中实施访问控制策略，开发了使用加密原语的新数据管理技术。在加密强制访问控制中，数据所有者发布单个数据实例，该实例是部分加密的，并强制执行所有访问控制策略。该项目开发了一种基于XQuery的访问策略声明性语言，以及一种将这些策略应用于XML数据实例以生成单个、多重加密的XML视图的方法。然后，数据所有者可以在互联网上发布该视图，每个人都可以免费下载和传播它。关键的方面是，只有拥有正确密钥的用户才能访问XML文档的加密部分。持有不同密钥集的不同用户可以访问文档的不同部分。该项目还开发了一个XQuery解释器，使持有正确密钥的授权用户能够在加密视图上执行查询。解释器动态地解密数据，并且只解密回答查询所需的数据。开发了一种新的数据模型，称为保护树，它捕获各种键如何保护XML数据的不同部分。保护树是所建议方法的核心：一旦将安全策略应用于XML数据实例，它们就会生成一个保护树；形成用户查询输入的数据模型也被建模为保护树。这项研究的结果将适用于提供对XML文档的安全访问。项目网站（http://www.cs.washington.edu/homes/pjallen/cryptography.html）将用于免费传播结果；具体来说，是一个策略查询求值器（生成加密视图）、一个解密XQuery解释器（用于查询加密视图）和一个一致性检查器。该项目还将为网络信托领域提供教育和研究经验。

Information exchange via XML documents is a rapidly growing technology. However, to date, complex constraints of trust and confidentiality often prohibit the dissemination of data. Data that could safely be disseminated to others remains hidden behind firewalls. This project aims at producing lightweight tools that allows publication and dissemination of data while at the same time controlling how data is accessed. New data management techniques are developed that use cryptographic primitives in order to enforce access control policies in published XML documents. In cryptographically enforced access control, the data owner publishes a single data instance, which is partially encrypted, and which enforces all access control policies. The project develops a declarative language for access policies, based on XQuery, and a method for applying these policies to an XML data instance to produce a single, multiply-encrypted XML view. This view can then be published by the data owner on the Internet, and everyone can freely download and disseminate it. The crucial aspect is that only users having the right keys can access encrypted parts of the XML document. Different users holding different set of keys will have access to different parts of the document. The project also develops an XQuery interpreter to enable authorized users, holding the right keys, to execute queries on the encrypted view. The interpreter decrypts data on the fly, and only that data required to answer the query. A novel kind of data model, called protection tree, is developed which captures how various keys protect different parts of the XML data. The protection tree is central to the proposed approach: once the security policies are applied to the XML data instance, they produce a protection tree; and the data model that forms the input to the user queries is also modeled as a protection tree. The results of this research will be applicable to providing secure access to XML documents. The project Web site (http://www.cs.washington.edu/homes/pjallen/cryptography.html) will be used for free dissemination of results; specifically, a policy query evaluator (which produces the encrypted view), a decrypting XQuery interpreter (which is used to query the encrypted view), and a consistency checker. This project will also provide educational and research experience in the Cyber Trust area.