Obfuscation of Abstract Data-Types - Rowan

Preliminaries
Homer: “All right brain, you don’t like me and I don’t like you.
But let’s just do this and I can get back to killing you
with beer.”
The Simpsons — The Front (1993)
In this thesis, we consider the obfuscation of programs. “To Obfuscate”
means “To cast into darkness or shadow; to cloud, obscure”. From a Computer
Science perspective, an obfuscation is a behaviour-preserving program transformation
whose aim is to make a program “harder to understand”. Obfuscations
are applied to a program to make reverse engineering of the program more difficult.
Two concerns about an obfuscation are whether it preserves behaviour
(i.e. it is correct) and the degree to which it maintains efficiency.
Example
As an example of obfuscation, consider the program in Figure 1. The method
start takes an integer value array as input and the array is returned from the
method. But what does this method do to the elements of the array? The
obfuscation was achieved by using some of the methods outlined in this thesis.
Aims of the thesis
The current view of obfuscation (in particular, the paper by Collberg et al. [10])
concentrates on object-oriented programs. In [10], obfuscations for constructs
such as loops, arrays and methods are stated informally: without proofs of
correctness. Constructing proofs of correctness for imperative obfuscations is a
challenging task.
We offer an alternative approach based on data refinement and functional
programming. We want our approach to have the following objectives:
• to yield proofs of correctness (or even yield derivations) of all our obfuscations
• to use simple, established refinement techniques, leaving the ingenuity for
obfuscation
• to generalise obfuscations to make obfuscations more applicable.
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