The common key is contained within the 3DS in some complicated technical way that I do not have any comprehension of, but will likely require a hardware modification (likely, done before) or yes, some exploit of the system using files that are not encrypted (are there any?).
I am not familiar with how the DSi key was obtained, but I think it can be summarized as basically: people who knew what they were doing did some crazy hax, got the key, kept it a secret for awhile but eventually it leaked.
I am not familiar with how the DSi key was obtained, but I think it can be summarized as basically: people who knew what they were doing did some crazy hax, got the key, kept it a secret for awhile but eventually it leaked.