Randomed/encoded code

[James Dean via Digitalmars-d-learn]

I would like to encode code in such a way that each compilation 
produces "random" code as compared to what the previous 
compilation produced, but ultimately the same code is ran each 
time(same effect).

Basically we can code a function that does a job X in many 
different ways. Each way looks different in binary but does the 
same job(Same effect). I'd like a way to sort of randomly 
sample/generate the different functions that do the same job.


The easiest way to wrap your head around this is to realize that 
certain instructions and groups of instructions can be 
rearranged, producing a binary that is different but the effect 
is the same. Probably, ultimately, that is all that can be 
done(certain other tricks could possibly be added to increase the 
sampling coverage such as nop like instructions, dummy 
instructions, etc).

The main issue is how to take an actual D function and transform 
it in to a new D function, which, when ran, ultimately does the 
same thing as the original but is not the same "binary".

Encrypting is a subset of this problem as we can take any string 
and use it to encode the code then decrypt it. And this may be 
usable, but then the encryption and decryption instructions must 
somehow be randomizable, else we are back at square one. It might 
be easier though, to use the encryption method to randomize the 
original function since the encryption routine is known while the 
original function is not(as it could be any function).

I'm not looking for a mathematical solution, just something that 
works well in practice. i.e., The most skilled human reading the 
disassembly would find it very difficult to interpret what is 
going on. He might be able to figure out one encryption routine, 
say, but when he sees the "same code"(same effect) he will have 
to start from scratch to understand it because its been 
"randomized".

The best way I can see how to do this is to have a list of well 
known encoding routines that take an arbitrary function, encrypt 
it. Each routine can be "randomized" by using various techniques 
to disguise it such as those mentioned earlier. This expands the 
list of functions tremendously. If there are N functions and M 
different ways to alter each of those functions then there are 
N*M total functions that we can use to encrypt the original 
function. If we further allow function composition of these 
functions, then we can get several orders of magnitude of 
complexity with such as a few N.

The goal though, is to do this efficiently and effectively in a 
way that can be amended. It will be useful in copy protection and 
used with other techniques to make it much more effective. 
Ultimately the weak point with the encryption techniques is 
decryption the functions but by composing encryption routines 
makes it stronger.

Any ideas how to achieve this in D nicely?