Refactoring programs to secure information flows

Abstract

Adding a sound information flow security policy to an existing program is a difficult task that requires major analysis of andchanges to the program. In this paper we show how refactoring programs into distinct components of high and low security is a useful methodology to aid in the production of programs with sound information flow policies. Our methodology proceeds as follows. Given a program with no information flow controls, a program sliceris used to identify code that depends on high security inputs. High security code so identified is then refactored into a separate component, which may be accessed by the low security component via public method calls. A security policy that labels input data and checks the output points can then enforce the desired end-to-end security property. Controlled information releases can occur at explicit declassification points if deemed safe. The result is a well-engineered program with explicit interfaces between components of different security levels.