Homebrew How does the smash controller application work?

[Zarxrax]

I've dabbled in homebrew development a bit in the past, though I'm still quite noobish as a programmer. But I would possibly be interested in trying to make a homebrew alternative to the "smash controller" application which lets you control Smash for Wii U via your 3DS. The thing is, I have no idea how to go about seeing how the 3ds and Wii U actually talk to one another. Is this something that can be discovered and reverse engineered easily, or does nintendo have it locked tight with some sort of encryption? Any ideas or advice to get me started? Thanks.