Problem - Kevin Tafuro

12.5 Performing Constant Transforms on
Variables
Problem
Variables used frequently—such as in loops or counters—are difficult to obfuscate
without impacting the performance of the program.
Solution
Change variables by a constant value.
Discussion
Changing variables by a constant value is a trivial form of obfuscation; however, it is
fast and easy to implement, and it can be combined with other obfuscation methods.
Here is an example of the obfuscation:
#define SET_VAR(var) (((var) * 3) + 0x01040200)
#define GET_VAR(var) (((var) - 0x01040200) / 3)
The macros can be applied to any usage of an integer:
for (i = SET_VAR(0); GET_VAR(i) < 10; i = SET_VAR(j + 1)) {
j = GET_VAR(i);
printf("2 + %d = %d\n", i, 2 + GET_VAR(i));
}
Constant transforms are useful only if the SET_VAR and GET_VAR macros are used far
apart; otherwise, the transform is immediately obvious. Transformations that are
more robust can be created that use different mathematical operations in each of the
SET_VAR and GET_VAR macros so that different constants are used in the expansion of
each macro. Note that the SET_VAR macro can be used in the initialization of a variable,
which will obfuscate the value of the variable at compile time.
12.6 Merging Scalar Variables
Problem
Scalar variables with constant or initialized values disclose information about ranges
of values.
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