In the problem of information sharing, two goals must be met to fulfil the requirements of both information providers and information consumers. That is, the information providers have constraints of data security/privacy protection, while the information consumers are interested in particular information and want to acquire such information as much as possible.;To solve this problem, disclosure algorithms are applied in the information disclosure process so information providers can compute what to share.;However, in a typical information disclosure process, the applied disclosure algorithm is constructed to check the goals solely on the exact disclosed data of the algorithm's output. This leads to serious security problems in that a malicious information consumer, or namely, the adversary, may be able to acquire additional information from the disclosure algorithm itself that violates the security/privacy constraints of the information providers.;This dissertation presents a number of techniques for answering basic questions about the problem of information sharing: how secure is an information disclosure process, when the disclosure algorithm is known to the public, and if it is not secure, how can we make it so?;This dissertation starts by extending an existing solution to the problem of online query auditing, i.e., whether a posed information request from the information consumer should be permitted or not.;In the problem of online query auditing, an adversary may acquire more precise information than what has been disclosed by the information providers based on the knowledge he or she obtained from the fact that some information requests have been denied. The existing solution, called simulatable auditing, does solve the problem partially by achieving the first goal, which is guaranteeing the security constraints of the information provider. However, it fails to achieve the second goal. That is, many information requests from information consumers will be denied unnecessarily to cause a significant data availability downgrade. This dissertation proposes a new solution that achieves both of the goals by identifying a sufficient and necessary condition for guaranteeing the data protection of the information providers.;This dissertation then studies a more relaxed problem, the problem of micro-data disclosure, in which the disclosure algorithm has to choose what to disclose from multiple candidate data/datasets. The problem of checking whether the security/privacy protection of the information provider has been violated turns out to be much harder in this case, i.e., the general case is an NP-complete problem. This problem has not been given enough attention, and most existing solutions suffer from a failure of the desired data security/privacy protection. This dissertation presents a new model to design safe disclosure algorithms that at least guarantee the data protection of the information providers. Heuristic algorithm design is also proposed to achieve an acceptable good performance for real-life data applications due to the hardness of the problem.;Finally, this dissertation addresses an open problem of how to restore the data security/privacy when it has already been compromised by incidental data disclosure, which is unavoidable when multiple information providers are disclosing the same set of information without collaboration or centralized control. This dissertation shows that, under certain conditions, this can be accomplished by applying a statistical approach.
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