Secure databases: Constraints, inference channels, and monitoring disclosures

This paper investigates the problem of inference channels that occur when database constraints are combined with nonsensitive data to obtain sensitive information. We present an integrated security mechanism, called the Disclosure Monitor, which guarantees data confidentiality by extending the standard mandatory access control mechanism with a Disclosure Inference Engine. The Disclosure Inference Engine generated all the information that can be disclosed to a user based on the user's past and present queries and the database and metadata constraints. The Disclosure Inference Engine operates in two modes:data-dependent mode, when disclosure is established based on the actual data items, and data-independent mode, when only queries are utilized to generate the disclosed information. The disclosure inference algorithms for both modes are characterized by the properties of soundness (i.e., everything that is generated by the algorithm is disclosed) and completeness (i.e,, everything that can be disclosed is produced by the algorithm). The technical core of this paper concentrates on the development of sound and complete algorithms for both data-dependent and data-independent disclosures.