Secure Query Answering for Outsourced Databases in Cloud Computing

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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.