A constraint-based query modification engine for retrofitting COTS DBMS´s

Models have been proposed to ensure the secrecy of data using various strategies. A number of these models however do not adequately address the problem of inference. This paper describes the design and implementation of a prototype that uses query modification along with security constraints to accurately return the proper information to the user whilst preventing unauthorized disclosure of data. The strategy works by augmenting a user´s query with security constraints to ensure that the modified query is correct and safe in relation to the user´s clearance level. The prototype is an implementation and extension of the query modification technique proposed by Keefe.