Yuan Xiang Gu

An Approach to the Obfuscation of Control-Flow of Sequential Computer Programs

In this paper we present a straightforward approach to the obfuscation of sequential program control-flow in order to design tamperresistant software. The principal idea of our technique is as follows: Let I be an instance of a hard combinatorial problem C, whose solution K is known. Then, given a source program ?, we implant I into ? by applying semantics-preserving transformations and using K as a key. This yields as its result an obfuscated program ?I,K, such that a detection of some property P of ?I,K, which is essential for comprehending the program, gives a solution to I. Varying instances I, we obtain a family ?C of obfuscated programs such that the problem of checking P for ?C is at least as hard as C. We show how this technique works by taking for C the acceptance problem for linear bounded Turing machines, which is known to be pspace-complete.

Information hiding in software with mixed Boolean-arithmetic transforms

As increasingly powerful software analysis and attack tools arise, we need increasingly potent software protections. We generate an unlimited supply of obscuring transforms via mixed-mode computation over Boolean-arithmetic (mba) algebras corresponding to real-world functions and data. Such transforms resist reverse engineering with existing advanced tools and create NP-hard problems for the attacker. We discuss broad uses and concrete applications to aacs key hiding and software watermarking.

A compiler-based infrastructure for software-protection

Not long after the introduction of stored-program computing machines, the first high-level language compilers appeared. The need for automatically and efficiently mapping abstract concepts from high-level languages onto low-level assembly languages has been recognized ever since. A compiler has a unique ability to gather and analyze large amounts of data in a manner that would be an unwieldy manual endeavor. It is this property that makes known compiler techniques and technology ideally suited for the purposes of software protection against reverse engineering and tampering attacks. In this paper, we present a code transformation infrastructure combined with build-time security techniques that are used to integrate protection into otherwise vulnerable machine programs. We show the applicability of known compiler techniques such as aliasanalysis, whole program analysis, data-flow analysis, and control-flow analysis and how these capabilities provide the basis for program transformations that provide comprehensive software protection. These methods are incorporated in an extensible framework allowing efficient development of new code transformations, as part of a larger suite of security tools for the creation of robust applications. We describe a number of successful applications of these tools.