As an example, I once reverse engineered encryption for data files in a game. Took me about three weeks to determine which encryption algorithm was being used,

As an example, I once reverse engineered encryption for data files in a game. Took me about three weeks to determine which encryption algorithm was being used, and what the key was (including learning some ARM along the way). But I was fortunate in that I could run the game in the debugger and see what was happening, the path from reading the data to decrypting it was rather simple to figure out, and the algorithm was pretty easy to spot. If I were to reverse engineer the actual asset formats I'd imagine it would take months as you need to know how everything is tied together in order to make sense of what is happening. It looks like in the case of guitar hero, this guy has spent an extortionate amount of time reverse engineering everything.