Reverse Engineering Using Memory Inspection and Numerical Analysis

One of the more recent tools I’ve added to my repertoire for reverse engineering the game simulation is inspecting the memory of a running game to see how things vary without needing to pause the game and count individual tiles in the game many times.

Power Plants and Cheat Engine:

To calculate the MW rating for power plants to tiles powered I could have built a city and connected a power plant to it and then counted the number of powered tiles, but the game has a variable that stores the total power produced. I could just build a city and look at this value, swapping power plants out as needed.

My go to tool for finding, viewing (and sometimes editing) values in memory is Cheat Engine. I use it to search for a known value, pulled from the save file, and then I get the value at that memory location. SC2k always uses the same memory addresses each time it starts up, so I slowly built up a table of where memory locations end up, at least for the common stuff.

Why didn’t I just build the plant, pause, save, load it into my parser and look at the value? Memory inspection is way faster after the initial discovery, and allowed me to more rapidly test other things.

cheatengine values.PNG
Cheat Engine address table showing some of the interesting addressed. The total amount of power produced is highlighted.

Once I found the total power variable, it was pretty quick to calculate that the MW rating for power plants doesn’t actually mean anything and each power plant has an internal statistic for how many tiles it powers, including the tiles that make up the plant itself!
For more info, see the spec here.

Weather – Beyond Cheat Engine:

But what happens when I want to look at the correlation between various values over many game cycles? Does weather, specifically temperature, affect the crime rate? If so, how much? Weather definitely affects how much electricity solar and wind power plants produce as well as how much water is pumped, but what’s the formula there?

Basically, how do I get those values from the running game and make decisions on it?

I’m still working on answering that question, but at it’s most basic level, I want to read various memory values once per tick of the game. The tick count is also used to determine the date of the game, which starts at a certain epoch.

So I wrote a simple python program the dumps values at memory locations once per game tick and another that uses pandas, numpy and matplotlib to do some analysis.

For power plants, I didn’t need anything fancy. I could see by quick inspection of values that wind power is indeed strongly affected by altitude and to a lesser extent how windy it is. Solar power is also affected by how humid it is, but both also have a random component involved. The simulation specification documents show how the weather affects wind and solar power in greater detail.

But what does this “look” like? I logged several hundred thousand values and created a correlation graph using numpy, pandas and matplotlib and a city containing a single power plant and a single water pump.

power water correlation
Correlation between (solar) power and water production.

What’s this graph telling us? Well, solar power production is negatively correlated with how humid (-0.298) and windy (-0.245) it is. Not knowing exactly what this represents in the game, it seems that higher values are probably rainier. I didn’t bin the weather the same way, as the game treats it like discrete values rather than the “continuous” values for humidity and windiness. So solar power is definitely affected by weather. On the other hand, it looks like water production is positively impacted by the weather (0.486 correlation with humidity and 0.242 with windiness) which seems like in rainy weather pumps produces more water. This is about what the game does.

But what about crime? Below is a correlation graph generated the same way.

crime weather correlation
Correlation between crime and various game weather variables. The diagonal line are how much a thing correlates with itself, which is always 1.0 or completely correlated, as expected.

So what sort of correlation do we see between crime and how hot it is? Almost none, but there is a slight correlation, 0.0287, so it does affect the simulation a little bit. Unsurprisingly, the type of weather is well correlated with wind (0.525), humidity (0.877) and heat (0.287). This isn’t enough to know how the formula works, because there is randomness at work, but it’s a start to figuring it out.

I’m not sure if this sort of analysis is actually going to be useful working to reverse engineer the game, but it’s definitely a useful place to get started, and may yet be a useful tool to determine exactly what is happening internal to the simulation.

 

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