Secure Programming Cookbook for C and C++

12.10. Restructuring Arrays

Problem

Arrays contain information in their structure. Knowing how many dimensions an array has can help in understanding the underlying data. You need a way to hide dimensional information about arrays.

Solution

Disguising the nature of arrays is different from obfuscating a variable. What is important in this case is the order of elements in the array, not the elements themselves. Array elements can be obfuscated using any standard variable obfuscation, but arrays themselves should be restructured as well.

Arrays can be restructured in four ways:

• Splitting a one-dimensional array into multiple one-dimension arrays

• Folding a one-dimensional array into a multidimensional array

• Flattening a multidimensional array into a one-dimensional array

• Merging two one-dimensional arrays into a single one-dimensional array

In this recipe, an API will be developed for splitting, folding, flattening, and merging arrays.

Discussion

Tip

Array obfuscation is a powerful way of disguising groupings of information by adding or subtracting dimensions from an array. Note that the array data is not obfuscated, merely the ordering of the data. This is insignificant with one-dimensional arrays but can be very effective with large multidimensional arrays.

The first step in developing the API for restructuring arrays is to define a new data type that will represent an array, rather than using the normal C convention for arrays. This array type will hide the management of the array restructuring ...