Abstract. In recent years, many have suggested to apply encryption in the domain of software protection against malicious hosts. However, little information seems to be available on the implementation aspects or cost of the different schemes. This paper tries to fill the gap by presenting our experience with several encryption techniques: bulk encryption, an ondemand decryption scheme, and a combination of both techniques. Our scheme offers maximal protection against both static and dynamic code analysis and tampering. We validate our techniques by applying them on several benchmark programs of the CPU2006 Test Suite. And finally, we propose a heuristic which trades off security versus performance, resulting in a decrease of the runtime overhead.

This paper proposes a general model for hiding control flow graph flattening in C programs. We explain what control flow graph flattening is and illustrate why it is successful as protection against static control flow analysis. Furthermore, we propose a scheme, complementary to control flow graph flattening, which does not leak any control flow graph information statically. Instead of relying on ad hoc security by using variable aliasing and global pointers to complicate data flow analysis of the switch variable, we try to base our security claims more on information theory, data flow, and cryptography. Our formal model is structured and extendable. Moreover, it can specify which minimum of information to hide from the program (e.g. a secret value or function) such that no control flow information is leaked. To express the robustness of our scheme we present some attacks and their feasibility. Finally, we sketch a few scenarios in which our solution could be deployed.