Secure Query Answering for Outsourced Databases in Cloud Computing

云计算通过由称为云的第三方托管的强大且可配置的计算资源提供按需高质量的服务，无疑是处理大数据的一种有效方法。云计算的一个应用是“数据库即服务”，即数据所有者将复杂的数据库管理系统外包到云中。这个应用的一个主要障碍是敏感数据的机密性，因为云服务器不受数据所有者的控制，不受信任。为了保护数据隐私和机密性，敏感数据必须在外包到云服务器之前进行加密。然而，这使得传统的查询处理方法(如索引)不再适用，因为所有这些方法都是在明文数据上操作的。因此，对加密数据的查询处理是一个新的研究课题，具有极其重要的意义。**有三个要求需要解决。第一个是机密性，即云服务器不应该通过存储数据和计算查询来了解查询结果以外的任何东西。第二种是身份验证，如果服务器不遵循规定的协议或篡改数据或查询结果，用户应该能够检测到事件的发生。第三个是效率，即该方法应可扩展到云规模的数据。这需要直接处理加密数据的索引和计算方法，而无需扫描整个数据库。密码学传统上是一个解决第一个需求的领域，但所开发的方法不能扩展到云规模，因为通常需要对数据库进行全面扫描。数据库和信息检索的最新发展解决了其中一些问题，但据我们所知，没有一项工作解决所有这三个要求。此外，数据是动态增长的，必须随着时间的推移满足上述要求。初步研究表明，在某种宽松的机密性要求下，对于某些类型的查询，解决所有上述要求的“可搜索加密”是可能的。这项提议的目的是调查可搜索性和保密性之间的权衡，并为更大类别的查询提出可搜索加密的解决方案，同时提供实际上可接受的保密性。该方案的创新之处在于结合了数据库、密码学和信息检索的技术，这三种技术传统上有不同的侧重点，以解决这一具有挑战性的问题。该项目的成果将为更安全地执行云计算提供方法，从而使所有数据所有者、云服务器和数据用户受益。

Cloud computing is no doubt an effective approach to deal with "big data", through providing on-demand high quality services from powerful and configurable computing resources hosted by a third party called the cloud. One application of cloud computing is "database as a service", where the data owner outsources complex database management systems into the cloud. A major obstacle to this application is the confidentiality of sensitive data since the cloud server is not under the control of the data owner and is untrusted. To protect data privacy and confidentiality, sensitive data must be encrypted before being outsourced to the cloud server. This, however, renders traditional query processing methods (such as indexing) inapplicable because all such methods operate on the plaintext data. Thus, query processing over encrypted data is a new research issue and of paramount importance. **There are three requirements to be addressed. The first is confidentiality, that is, the cloud server should not learn anything other than the query result through storing the data and computing the query. The second is authentication where the user should be able to detect the occurrence of the event if the server does not follow the prescribed protocol or tampers with the data or query result. The third is efficiency where the method should be scalable to data at the cloud scale. This requires indexing and computational methods that work directly on encrypted data without scanning the entire database. Cryptography is traditionally a field addressing the first requirement, but the methods developed do not scale up to the cloud scale because a full scan of database often is required. Recent developments in databases and information retrieval address some of these issues, but to our knowledge, no work has addressed all three requirements. In addition, data grows dynamically and the above requirements must be met over time. Initial studies suggest that a "searchable encryption" that addresses all of the above requirements is possible for certain types of queries under some relaxed requirement of confidentiality. The objective of this proposal is to investigate the trade-off between searchability and confidentiality and propose solutions to searchable encryption for larger classes of queries while providing practically acceptable confidentiality. The innovation of this proposal is combining the techniques from databases, cryptography, and information retrieval, which traditionally has different focuses, to address this challenging problem. The outcome of this project will provide methodologies for more secure execution of cloud computing, therefore, benefit all of the data owners, cloud servers, and data users.