A Goal-Oriented Approach to Software Obfuscation

Various software obfuscation techniques have been proposed. However, there are few discussions on proper use of these obfuscations against imaginable threats. An ad- hoc use of obfuscations cannot guarantee that a program is sufficiently protected. For a systematic use of obfuscations and the verification of the result, this paper proposes a goal oriented approach to obfuscation. Specifically, we (1) define the capability of an imaginary cracker, (2) identify the cracker's goal, (3) conduct a goaloriented analysis, (4) select obfuscations to disrupt all subgoals, and (5) apply selected obfuscations to the program. As a case study, we define a security goal and a threat model for a Java implementation of a cryptomeria cipher (C2) program, and then, based on the model, we demonstrate how the goal oriented analysis is conducted and obfuscation techniques are applied to places where they are needed.