Research On Private Information Retrieval Technology

With the rapid development of the information communication technology, usingnetwork for information storage and exchange has become a normal style for people’sworking and living. However, because of the complexity of the network environment andthe uncertainty of the user behavior, the client privacy can not be protected well. It isimportant to provide some methods to protect the clients’ private information. Privateinformation retrieval (PIR) was proposed to resolve such a problem: when clients retrievedata from a database, the intension of these queries should be hidden. For the existingproblems in PIR research such as high complexity, short of privacy metric, short ofcombination with database, etc, focusing on the PIR protocol, privacy metric, etc, weconduct deep research on four aspects.In order to lower the complexity of PIR protocols, a row based computational PIRprotocol called Robac-PIR is designed, which is improved on quadratic residuosity PIR. InRobac-PIR, queries are made on part of the data instead of the whole data in the server, sothat the client is able to make a tradeoff between privacy and efficiency. Furtherimprovement is made on Robac-PIR to propose a network enviroment PIR scheme. In thisscheme, data blocks are distributed to different client nodes in the network to share thecomputation work and the overall efficiency is increased. The experiments show that ourRobac-PIR protocol and distributed Robac-PIR scheme are flexible and superior inefficiency.In order to improve the practicability of PIR protocol, a keyword based PIR scheme isproposed to protect the client privacy in discovery service (DS) of internet of things. ThePIR scheme is based on hash index and well applicable to DS environment. Comparedwith existing client privacy preserving DS architectures, this scheme doesn’t need toworry about the collaboration between servers, complex pre-distribution of keys, and cancompletely protect the client privacy by private information retrieval.To resolve the problem that privacy metric is lacked in PIR research, based oninformation theory, the definition and the quantitative method are made for the clientquery privacy in PIR problem. Quantification and analysis are made for our Robac-PIRprotocol and some other existing PIR protocols using the proposed formula of quantifying.Analysis shows that our privacy metric does well for the client query privacy Nowadays there isn’t any design of the database system providing PIR query. Toresolve this problem, formal specification and verification are made on the design of thedatabase providing PIR query. On the client side, the PIR transformations for queries areanalysed and verified. On the server side, the model and the formal top-level specification(FTLS) are proposed for the database system. Proof assistant tool COQ is used to specifyand verify the FTLS of the database system, especially the PIR query operation within.The verification shows that the design of the database system and the query operationsatisfies the security properties in the security policy.