Obfuscation of Abstract Data-Types - Rowan

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CHAPTER 1. OBFUSCATION 21 • Outlining A sequence of statements within a method is made into a separate method. • Interleaving Two methods are merged; to distinguish between the original methods, an extra parameter could be passed. • Cloning Many copies of the same method are created by applying different transformations. 1.4 Conclusions We have seen there is a need for software protection, and code obfuscation is one method for making reverse engineering harder. We have summarised some current obfuscation techniques and highlighted a few of the many commercial obfuscators available. In Section 1.2 we reviewed two definitions of obfuscation: the definition of Collberg et al. [10] uses various complexity metrics and Barak et al. [6] prove that obfuscation is impossible using their definition. We have seen how to apply obfuscations to variables and arrays. In Chapter 3 we shall develop a different approach to obfuscation which enables us to apply obfuscations to more abstract data structures. As a consequence we will give a new definition for obfuscation and also discuss the efficiency of obfuscated operations. In the next chapter, we give a case study of a situation where there is a particular need for obfuscation and give specifications for some obfuscations.
Chapter 2 Obfuscations for Intermediate Language ...if you stick a Babel fish in your ear you can instantly understand anything said to you in any form of language The Hitchhiker’s Guide to the Galaxy (1979) Before we look at a new approach to obfuscation, we present a case study in which we explore a potential application of obfuscation. We look at the intermediate language that is part of Microsoft’s .NET platform and we give some obfuscations for this language. In particular, we specify some generalisations of some of the obfuscations given in Section 1.3. 2.1 .NET The heart of Microsoft’s .NET framework is the Common Language Infrastructure [23] which consists of an intermediate language (IL) which has been designed to be the compilation target for various source languages. IL is a typed stack based language and since it is at quite a high level, it is fairly easy to decompile IL to C# [3]. Two example decompilers are Anakrino [2] and Salamander [45]. IL is similar to Java bytecode but more complicated as it is the compilation target for various languages. Programs written using .NET are distributed as portable executables (PEs) which are compact representations of IL. These executables are then just-intime compiled on the target platform. We can translate a PE to IL by using a disassembler and we can convert back by using an assembler. This means that from a PE we can disassemble back to IL and then decompile back to C#. Since we can convert a PE to C#, there is a need for obfuscation. 2.1.1 IL Instructions Before we describe some IL obfuscations, we give a brief overview of IL. We concentrate on a fragment of IL — the instructions of interest are shown in 22
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CHAPTER 6. THE MATRIX OBFUSCATED 10
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Chapter 8 Conclusions and Further W
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CHAPTER 8. CONCLUSIONS AND FURTHER
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CHAPTER 8. CONCLUSIONS AND FURTHER
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BIBLIOGRAPHY 140 [13] Thomas H. Cor
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BIBLIOGRAPHY 142 [43] Simon Peyton
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Appendix A List assertion We want t
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APPENDIX A. LIST ASSERTION 146 Case
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APPENDIX B. SET OPERATIONS 160 Now
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APPENDIX B. SET OPERATIONS 162 Proo
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APPENDIX B. SET OPERATIONS 164 B.2
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Appendix C Matrices We prove the as
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APPENDIX C. MATRICES 168 Base Case
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APPENDIX E. OBFUSCATION EXAMPLE 186
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