The time has come for me to tell the story of how I came to own the domain reenigne.org, and hence the reason why this blog is called what it is called.
The story I tell on the site is that I reverse-engineered Digger, hence "reverse engineer" or "reenigne". That's only part of the story though. My experience doing this manual reverse-engineering project (and a couple of others) convinced me that building a tool to aid in decompilation would be an interesting project. I decided to call this tool Reenigne and bought the domain name for the project. I set up my personal website there as a temporary measure but when I got a job with Microsoft, Reenigne (the program) got put on the back burner.
Decompilation (or, more generally, analysis of programs) is an interesting problem in general. An important result in theoretical computer science (the undecidability of the halting problem) says that it's impossible to write a program that even determines if a given input program halts or not, let alone analyses it to the extent that Reenigne would have to in order to be useful.
But that theorem only applies to infinite computers. If you know in advance the maximum memory that the program can use you can simulate a machine running the program and detect if it gets into a looping state. Not tremendously useful since that could still be many orders of magnitude more data than today's computers have even for the simplest programs. Does it matter for real-world programs? Well maybe not for early 80s games...
Another advantage we have over the Turing machines in the halting problem is an oracle - a human operator. If Reenigne gets stuck analyzing a particular program it can ask for human help. A human may be able to spot paths of execution or quickly prove things that the computer working alone cannot do. Together (the idea goes) Reenigne and a human operator form an unbeatable team that can reverse-engineer any real world program to source code quickly and (relatively) easily (assuming some knowledge of what the program does and how it might work). The human inputs to Reenigne can in principle be recorded to form a script which can be played back to enable anyone who has a copy of the same binary program to obtain the source code. The source code itself could not be distributed (it's copyrighted) but as far as I can tell the Reenigne scripts could be arbitrarily distributed - they're not a derivative work of the binary program, they are more like a commentary on it (I even thought about having the program save these scripts with the extension ".commentary" to hammer this point home extra hard).
Assuming that .commentary files for any piece of software are easily available, you can obtain source code for any binary you have - effectively making any program open in the same way that GPL software is (although with the minor restriction that you cannot legally redistribute the program itself). As I'm sure you can imagine, such a state of affairs would scare the bejeezus out of Microsoft. That's not the reason I haven't written it though - it's just lack of time.
The game doesn't end there though - for any possible Reenigne it's possible to write a program in such a way as to maximizes the difficulty in reverse-engineering it with that particular Reenigne (by twisting up the logic to make it hard for a human to see what's going on, and by causing the program to have to do things like prove Fermat's Last Theorem just to find all the code in amongst random distracting junk). This would make programs slower and could never eliminate the threat of reverse-engineering completely (as I said, it's always possible in theory to simulate the program on a bigger computer so any roadblocks would just pose engineering problems, not theoretical problems). But given the lengths that some software misguidedly goes to to keep its secrets from the owner of a computer whilst spilling those same secrets wide open to the CPU, I have no doubt that if a useful Reenigne were to become available, all these tricks would be tried.
We would then enter a period of "arms racing" between the Reenigne-creators (which, I am assuming, would be more than just me by then) and those trying to keep their algorithms and content decryption keys secret. They add a Reenigne-defeating trick, then a new version of Reenigne appears which understands and works around that trick, and so on.
Given the propensity of the US government to pass laws like the DMCA (aka the "Snake Oil protection act") and arrest computer programmers for doing their jobs, I suspect it would be unwise for me to pursue Reenigne seriously whilst living in the US (at least while the political climate is still so pro-"intellectual property").
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